avcodec_send_packet和avcodec_receive_frame是一对孪生兄弟࿰c;avcodec_send_packet把需要解码的AVPacket送到解码器中࿰c;avcodec_receive_frame则是得到解码完成后的frame。
这两个函数都是通过调用decode_receive_frame_internal来实现的。

codec_send_packet__4">avcodec_send_packet 作用

把未经过解码的AVPacket送到AVCodecContext中解码。
FFmpeg的说明如下：

<code class="prism language-c">class="token comment">/**
 * Supply raw packet data as input to a decoder.
 *
 * Internally, this call will copy relevant AVCodecContext fields, which can
 * influence decoding per-packet, and apply them when the packet is actually
 * decoded. (For example AVCodecContext.skip_frame, which might direct the
 * decoder to drop the frame contained by the packet sent with this function.)
 *
 * @return 0 on success, otherwise negative error code:
 *      AVERROR(EAGAIN):   input is not accepted in the current state - user
 *                         must read output with avcodec_receive_frame() (once
 *                         all output is read, the packet should be resent, and
 *                         the call will not fail with EAGAIN).
 *      AVERROR_EOF:       the decoder has been flushed, and no new packets can
 *                         be sent to it (also returned if more than 1 flush
 *                         packet is sent)
 *      AVERROR(EINVAL):   codec not opened, it is an encoder, or requires flush
 *      AVERROR(ENOMEM):   failed to add packet to internal queue, or similar
 *      other errors: legitimate decoding errors
 */
class="token keyword">int class="token function">avcodec_send_packetclass="token punctuation">(AVCodecContext class="token operator">*avctxclass="token punctuation">, class="token keyword">const AVPacket class="token operator">*avpktclass="token punctuation">)class="token punctuation">;

class="token comment">/**
 * Supply a raw video or audio frame to the encoder. Use avcodec_receive_packet()
 * to retrieve buffered output packets.
 * @return 0 on success, otherwise negative error code:
 *      AVERROR(EAGAIN):   input is not accepted in the current state - user
 *                         must read output with avcodec_receive_packet() (once
 *                         all output is read, the packet should be resent, and
 *                         the call will not fail with EAGAIN).
 *      AVERROR_EOF:       the encoder has been flushed, and no new frames can
 *                         be sent to it
 *      AVERROR(EINVAL):   codec not opened, refcounted_frames not set, it is a
 *                         decoder, or requires flush
 *      AVERROR(ENOMEM):   failed to add packet to internal queue, or similar
 *      other errors: legitimate encoding errors
 */
class="token keyword">int class="token function">avcodec_send_frameclass="token punctuation">(AVCodecContext class="token operator">*avctxclass="token punctuation">, class="token keyword">const AVFrame class="token operator">*frameclass="token punctuation">)class="token punctuation">;
code>

简而言之࿰c;avcodec_send_packet就是把AVPacket送到AVCodecContext࿰c;然后让AVCodecContext解码。avcodec_receive_frame获得解码后的AVFrame。
需要注意的是࿰c;AVCodecContext必须经过avcodec_open2函数打开࿰c;输入的AVPacket会在内部增加一个ref࿰c;所以如果要free࿰c;外部也应该调用av_packet_unref。

codec_send_packet__50">avcodec_send_packet 源码

把avpk送到avci->bsf中࿰c;等待解码。然后通过判断avci->buffer_frame->buf[0]是否null来决定是否调用decode_receive_frame_internal来接受解码后的frame。

<code class="prism language-c">class="token keyword">int attribute_align_arg class="token function">avcodec_send_packetclass="token punctuation">(AVCodecContext class="token operator">*avctxclass="token punctuation">, class="token keyword">const AVPacket class="token operator">*avpktclass="token punctuation">)
class="token punctuation">{
    AVCodecInternal class="token operator">*avci class="token operator">= avctxclass="token operator">->internalclass="token punctuation">;
    class="token keyword">int retclass="token punctuation">;

	class="token comment">// 未open和编码器都不行
    class="token keyword">if class="token punctuation">(class="token operator">!class="token function">avcodec_is_openclass="token punctuation">(avctxclass="token punctuation">) class="token operator">|| class="token operator">!class="token function">av_codec_is_decoderclass="token punctuation">(avctxclass="token operator">->codecclass="token punctuation">)class="token punctuation">)
        class="token keyword">return class="token function">AVERRORclass="token punctuation">(EINVALclass="token punctuation">)class="token punctuation">;

	class="token comment">// 检测是否应该先flush
    class="token keyword">if class="token punctuation">(avctxclass="token operator">->internalclass="token operator">->drainingclass="token punctuation">)
        class="token keyword">return AVERROR_EOFclass="token punctuation">;

    class="token keyword">if class="token punctuation">(avpkt class="token operator">&& class="token operator">!avpktclass="token operator">->size class="token operator">&& avpktclass="token operator">->dataclass="token punctuation">)
        class="token keyword">return class="token function">AVERRORclass="token punctuation">(EINVALclass="token punctuation">)class="token punctuation">;

    class="token function">av_packet_unrefclass="token punctuation">(avciclass="token operator">->buffer_pktclass="token punctuation">)class="token punctuation">;
    class="token comment">// avci->buffer_pkt也reference输入的avpkt
    class="token comment">// 相当于一次copy （不一定是深copy）
    class="token keyword">if class="token punctuation">(avpkt class="token operator">&& class="token punctuation">(avpktclass="token operator">->data class="token operator">|| avpktclass="token operator">->side_data_elemsclass="token punctuation">)class="token punctuation">) class="token punctuation">{
        ret class="token operator">= class="token function">av_packet_refclass="token punctuation">(avciclass="token operator">->buffer_pktclass="token punctuation">, avpktclass="token punctuation">)class="token punctuation">;
        class="token keyword">if class="token punctuation">(ret class="token operator">< class="token number">0class="token punctuation">)
            class="token keyword">return retclass="token punctuation">;
    class="token punctuation">}

	class="token comment">// 把avci->buffer_pkt送到avci->bsf中
	class="token comment">// 即将avci->buffer_pkt copy到avci->bsf->internal->buffer_pkt࿰c;然后可以经过bsf。
	class="token comment">// AVBSFContext一般是对AVPacket进行某些格式上的转换࿰c;比如对h264来说࿰c;存在AVCC和ANNEXB两种格式࿰c;这里就是把AVCC格式转换成为ANNEXB
    ret class="token operator">= class="token function">av_bsf_send_packetclass="token punctuation">(avciclass="token operator">->bsfclass="token punctuation">, avciclass="token operator">->buffer_pktclass="token punctuation">)class="token punctuation">;
    class="token keyword">if class="token punctuation">(ret class="token operator">< class="token number">0class="token punctuation">) class="token punctuation">{
        class="token function">av_packet_unrefclass="token punctuation">(avciclass="token operator">->buffer_pktclass="token punctuation">)class="token punctuation">;
        class="token keyword">return retclass="token punctuation">;
    class="token punctuation">}

    class="token keyword">if class="token punctuation">(class="token operator">!avciclass="token operator">->buffer_frameclass="token operator">->bufclass="token punctuation">[class="token number">0class="token punctuation">]class="token punctuation">) class="token punctuation">{
    	class="token comment">//这个函数会在avcodec_send_packet或者avcodec_receive_frame中调用
    	class="token comment">//avci->buffer_frame->buf[0]为null࿰c;就在avcodec_send_packet中调用
    	class="token comment">//avci->buffer_frame->buf[0]不为null࿰c;就在avcodec_receive_frame中调用
    	class="token comment">//decode_receive_frame_internal中
        ret class="token operator">= class="token function">decode_receive_frame_internalclass="token punctuation">(avctxclass="token punctuation">, avciclass="token operator">->buffer_frameclass="token punctuation">)class="token punctuation">;
        class="token keyword">if class="token punctuation">(ret class="token operator">< class="token number">0 class="token operator">&& ret class="token operator">!= class="token function">AVERRORclass="token punctuation">(EAGAINclass="token punctuation">) class="token operator">&& ret class="token operator">!= AVERROR_EOFclass="token punctuation">)
            class="token keyword">return retclass="token punctuation">;
    class="token punctuation">}

    class="token keyword">return class="token number">0class="token punctuation">;
class="token punctuation">}
code>

codec_receive_frame__100">avcodec_receive_frame 源码

<code class="prism language-c">class="token keyword">int attribute_align_arg class="token function">avcodec_receive_frameclass="token punctuation">(AVCodecContext class="token operator">*avctxclass="token punctuation">, AVFrame class="token operator">*frameclass="token punctuation">)
class="token punctuation">{
    AVCodecInternal class="token operator">*avci class="token operator">= avctxclass="token operator">->internalclass="token punctuation">;
    class="token keyword">int retclass="token punctuation">, changedclass="token punctuation">;

    class="token function">av_frame_unrefclass="token punctuation">(frameclass="token punctuation">)class="token punctuation">;

	class="token comment">// 判断是否调用过avcodec_open2函数࿰c;是否为解码器
    class="token keyword">if class="token punctuation">(class="token operator">!class="token function">avcodec_is_openclass="token punctuation">(avctxclass="token punctuation">) class="token operator">|| class="token operator">!class="token function">av_codec_is_decoderclass="token punctuation">(avctxclass="token operator">->codecclass="token punctuation">)class="token punctuation">)
        class="token keyword">return class="token function">AVERRORclass="token punctuation">(EINVALclass="token punctuation">)class="token punctuation">;

	class="token comment">// 根据avci->buffer_frame->buf[0]判断是否存在解码完成的帧࿰c;如果存在就直接move到frame中。
	class="token comment">// 如果没有就调用decode_receive_frame_internal把AVPacket送去解码线程࿰c;然后获得解码之后的AVFrame。
    class="token keyword">if class="token punctuation">(avciclass="token operator">->buffer_frameclass="token operator">->bufclass="token punctuation">[class="token number">0class="token punctuation">]class="token punctuation">) class="token punctuation">{
        class="token function">av_frame_move_refclass="token punctuation">(frameclass="token punctuation">, avciclass="token operator">->buffer_frameclass="token punctuation">)class="token punctuation">;
    class="token punctuation">} class="token keyword">else class="token punctuation">{
        ret class="token operator">= class="token function">decode_receive_frame_internalclass="token punctuation">(avctxclass="token punctuation">, frameclass="token punctuation">)class="token punctuation">;
        class="token keyword">if class="token punctuation">(ret class="token operator">< class="token number">0class="token punctuation">)
            class="token keyword">return retclass="token punctuation">;
    class="token punctuation">}

    class="token keyword">if class="token punctuation">(avctxclass="token operator">->codec_type class="token operator">== AVMEDIA_TYPE_VIDEOclass="token punctuation">) class="token punctuation">{
        ret class="token operator">= class="token function">apply_croppingclass="token punctuation">(avctxclass="token punctuation">, frameclass="token punctuation">)class="token punctuation">;
        class="token keyword">if class="token punctuation">(ret class="token operator">< class="token number">0class="token punctuation">) class="token punctuation">{
            class="token function">av_frame_unrefclass="token punctuation">(frameclass="token punctuation">)class="token punctuation">;
            class="token keyword">return retclass="token punctuation">;
        class="token punctuation">}
    class="token punctuation">}

    avctxclass="token operator">->frame_numberclass="token operator">++class="token punctuation">;

    class="token keyword">if class="token punctuation">(avctxclass="token operator">->flags class="token operator">& AV_CODEC_FLAG_DROPCHANGEDclass="token punctuation">) class="token punctuation">{

        class="token keyword">if class="token punctuation">(avctxclass="token operator">->frame_number class="token operator">== class="token number">1class="token punctuation">) class="token punctuation">{
            avciclass="token operator">->initial_format class="token operator">= frameclass="token operator">->formatclass="token punctuation">;
            class="token keyword">switchclass="token punctuation">(avctxclass="token operator">->codec_typeclass="token punctuation">) class="token punctuation">{
            class="token keyword">case AVMEDIA_TYPE_VIDEOclass="token operator">:
                avciclass="token operator">->initial_width  class="token operator">= frameclass="token operator">->widthclass="token punctuation">;
                avciclass="token operator">->initial_height class="token operator">= frameclass="token operator">->heightclass="token punctuation">;
                class="token keyword">breakclass="token punctuation">;
            class="token keyword">case AVMEDIA_TYPE_AUDIOclass="token operator">:
                avciclass="token operator">->initial_sample_rate class="token operator">= frameclass="token operator">->sample_rate class="token operator">? frameclass="token operator">->sample_rate class="token operator">:
                                                                 avctxclass="token operator">->sample_rateclass="token punctuation">;
                avciclass="token operator">->initial_channels       class="token operator">= frameclass="token operator">->channelsclass="token punctuation">;
                avciclass="token operator">->initial_channel_layout class="token operator">= frameclass="token operator">->channel_layoutclass="token punctuation">;
                class="token keyword">breakclass="token punctuation">;
            class="token punctuation">}
        class="token punctuation">}

        class="token keyword">if class="token punctuation">(avctxclass="token operator">->frame_number class="token operator">> class="token number">1class="token punctuation">) class="token punctuation">{
            changed class="token operator">= avciclass="token operator">->initial_format class="token operator">!= frameclass="token operator">->formatclass="token punctuation">;

            class="token keyword">switchclass="token punctuation">(avctxclass="token operator">->codec_typeclass="token punctuation">) class="token punctuation">{
            class="token keyword">case AVMEDIA_TYPE_VIDEOclass="token operator">:
                changed class="token operator">|= avciclass="token operator">->initial_width  class="token operator">!= frameclass="token operator">->width class="token operator">||
                           avciclass="token operator">->initial_height class="token operator">!= frameclass="token operator">->heightclass="token punctuation">;
                class="token keyword">breakclass="token punctuation">;
            class="token keyword">case AVMEDIA_TYPE_AUDIOclass="token operator">:
                changed class="token operator">|= avciclass="token operator">->initial_sample_rate    class="token operator">!= frameclass="token operator">->sample_rate class="token operator">||
                           avciclass="token operator">->initial_sample_rate    class="token operator">!= avctxclass="token operator">->sample_rate class="token operator">||
                           avciclass="token operator">->initial_channels       class="token operator">!= frameclass="token operator">->channels class="token operator">||
                           avciclass="token operator">->initial_channel_layout class="token operator">!= frameclass="token operator">->channel_layoutclass="token punctuation">;
                class="token keyword">breakclass="token punctuation">;
            class="token punctuation">}

            class="token keyword">if class="token punctuation">(changedclass="token punctuation">) class="token punctuation">{
                avciclass="token operator">->changed_frames_droppedclass="token operator">++class="token punctuation">;
                class="token function">av_logclass="token punctuation">(avctxclass="token punctuation">, AV_LOG_INFOclass="token punctuation">, class="token string">"dropped changed frame #%d pts %"PRId64
                                            class="token string">" drop count: %d \n"class="token punctuation">,
                                            avctxclass="token operator">->frame_numberclass="token punctuation">, frameclass="token operator">->ptsclass="token punctuation">,
                                            avciclass="token operator">->changed_frames_droppedclass="token punctuation">)class="token punctuation">;
                class="token function">av_frame_unrefclass="token punctuation">(frameclass="token punctuation">)class="token punctuation">;
                class="token keyword">return AVERROR_INPUT_CHANGEDclass="token punctuation">;
            class="token punctuation">}
        class="token punctuation">}
    class="token punctuation">}
    class="token keyword">return class="token number">0class="token punctuation">;
class="token punctuation">}
code>

code_receive_frame_internal__181">decode_receive_frame_internal 源码

获取解码后的frame。

<code class="prism language-c">class="token keyword">static class="token keyword">int class="token function">decode_receive_frame_internalclass="token punctuation">(AVCodecContext class="token operator">*avctxclass="token punctuation">, AVFrame class="token operator">*frameclass="token punctuation">)
class="token punctuation">{
    AVCodecInternal class="token operator">*avci class="token operator">= avctxclass="token operator">->internalclass="token punctuation">;
    class="token keyword">int retclass="token punctuation">;

    class="token function">av_assert0class="token punctuation">(class="token operator">!frameclass="token operator">->bufclass="token punctuation">[class="token number">0class="token punctuation">]class="token punctuation">)class="token punctuation">;

	class="token comment">// 只有少部分解码器会实现这个函数࿰c;实现这个函数的解码器不会实现多线程解码࿰c;比如mjpeg
    class="token keyword">if class="token punctuation">(avctxclass="token operator">->codecclass="token operator">->receive_frameclass="token punctuation">) class="token punctuation">{
        ret class="token operator">= avctxclass="token operator">->codecclass="token operator">->class="token function">receive_frameclass="token punctuation">(avctxclass="token punctuation">, frameclass="token punctuation">)class="token punctuation">;
        class="token keyword">if class="token punctuation">(ret class="token operator">!= class="token function">AVERRORclass="token punctuation">(EAGAINclass="token punctuation">)class="token punctuation">)
            class="token function">av_packet_unrefclass="token punctuation">(avciclass="token operator">->last_pkt_propsclass="token punctuation">)class="token punctuation">;
    class="token punctuation">} class="token keyword">else
    	class="token comment">//大部分都是调用这个函数
        ret class="token operator">= class="token function">decode_simple_receive_frameclass="token punctuation">(avctxclass="token punctuation">, frameclass="token punctuation">)class="token punctuation">;

    class="token keyword">if class="token punctuation">(ret class="token operator">== AVERROR_EOFclass="token punctuation">)
        avciclass="token operator">->draining_done class="token operator">= class="token number">1class="token punctuation">;

    class="token keyword">if class="token punctuation">(class="token operator">!retclass="token punctuation">) class="token punctuation">{
        frameclass="token operator">->best_effort_timestamp class="token operator">= class="token function">guess_correct_ptsclass="token punctuation">(avctxclass="token punctuation">,
                                                         frameclass="token operator">->ptsclass="token punctuation">,
                                                         frameclass="token operator">->pkt_dtsclass="token punctuation">)class="token punctuation">;

        class="token comment">/* the only case where decode data is not set should be decoders
         * that do not call ff_get_buffer() */
        class="token function">av_assert0class="token punctuation">(class="token punctuation">(frameclass="token operator">->private_ref class="token operator">&& frameclass="token operator">->private_refclass="token operator">->size class="token operator">== class="token keyword">sizeofclass="token punctuation">(FrameDecodeDataclass="token punctuation">)class="token punctuation">) class="token operator">||
                   class="token operator">!class="token punctuation">(avctxclass="token operator">->codecclass="token operator">->capabilities class="token operator">& AV_CODEC_CAP_DR1class="token punctuation">)class="token punctuation">)class="token punctuation">;

        class="token keyword">if class="token punctuation">(frameclass="token operator">->private_refclass="token punctuation">) class="token punctuation">{
            FrameDecodeData class="token operator">*fdd class="token operator">= class="token punctuation">(FrameDecodeDataclass="token operator">*class="token punctuation">)frameclass="token operator">->private_refclass="token operator">->dataclass="token punctuation">;

            class="token keyword">if class="token punctuation">(fddclass="token operator">->post_processclass="token punctuation">) class="token punctuation">{
                ret class="token operator">= fddclass="token operator">->class="token function">post_processclass="token punctuation">(avctxclass="token punctuation">, frameclass="token punctuation">)class="token punctuation">;
                class="token keyword">if class="token punctuation">(ret class="token operator">< class="token number">0class="token punctuation">) class="token punctuation">{
                    class="token function">av_frame_unrefclass="token punctuation">(frameclass="token punctuation">)class="token punctuation">;
                    class="token keyword">return retclass="token punctuation">;
                class="token punctuation">}
            class="token punctuation">}
        class="token punctuation">}
    class="token punctuation">}

    class="token comment">/* free the per-frame decode data */
    class="token function">av_buffer_unrefclass="token punctuation">(class="token operator">&frameclass="token operator">->private_refclass="token punctuation">)class="token punctuation">;

    class="token keyword">return retclass="token punctuation">;
class="token punctuation">}

code>

code_simple_receive_frame__234">decode_simple_receive_frame 源码

通过调用decode_simple_internal来实现解码AVPacket࿰c;然后获取解码后的frame。

<code class="prism language-c">class="token keyword">static class="token keyword">int class="token function">decode_simple_receive_frameclass="token punctuation">(AVCodecContext class="token operator">*avctxclass="token punctuation">, AVFrame class="token operator">*frameclass="token punctuation">)
class="token punctuation">{
    class="token keyword">int retclass="token punctuation">;
    class="token class-name">int64_t discarded_samples class="token operator">= class="token number">0class="token punctuation">;

    class="token keyword">while class="token punctuation">(class="token operator">!frameclass="token operator">->bufclass="token punctuation">[class="token number">0class="token punctuation">]class="token punctuation">) class="token punctuation">{
        class="token keyword">if class="token punctuation">(discarded_samples class="token operator">> avctxclass="token operator">->max_samplesclass="token punctuation">)
            class="token keyword">return class="token function">AVERRORclass="token punctuation">(EAGAINclass="token punctuation">)class="token punctuation">;
        ret class="token operator">= class="token function">decode_simple_internalclass="token punctuation">(avctxclass="token punctuation">, frameclass="token punctuation">, class="token operator">&discarded_samplesclass="token punctuation">)class="token punctuation">;
        class="token keyword">if class="token punctuation">(ret class="token operator">< class="token number">0class="token punctuation">)
            class="token keyword">return retclass="token punctuation">;
    class="token punctuation">}

    class="token keyword">return class="token number">0class="token punctuation">;
class="token punctuation">}
code>

code_simple_internal__254">decode_simple_internal 源码

avcodec_send_packet和avcodec_receive_frame中最核心的函数࿰c;大部分的编码格式都会调用到这里解码。

<code class="prism language-c">class="token comment">/*
 * The core of the receive_frame_wrapper for the decoders implementing
 * the simple API. Certain decoders might consume partial packets without
 * returning any output, so this function needs to be called in a loop until it
 * returns EAGAIN.
 **/
class="token keyword">static class="token keyword">inline class="token keyword">int class="token function">decode_simple_internalclass="token punctuation">(AVCodecContext class="token operator">*avctxclass="token punctuation">, AVFrame class="token operator">*frameclass="token punctuation">, class="token class-name">int64_t class="token operator">*discarded_samplesclass="token punctuation">)
class="token punctuation">{
    AVCodecInternal   class="token operator">*avci class="token operator">= avctxclass="token operator">->internalclass="token punctuation">;
    DecodeSimpleContext class="token operator">*ds class="token operator">= class="token operator">&avciclass="token operator">->dsclass="token punctuation">;
    AVPacket           class="token operator">*pkt class="token operator">= dsclass="token operator">->in_pktclass="token punctuation">;
    class="token keyword">int got_frameclass="token punctuation">, actual_got_frameclass="token punctuation">;
    class="token keyword">int retclass="token punctuation">;

    class="token keyword">if class="token punctuation">(class="token operator">!pktclass="token operator">->data class="token operator">&& class="token operator">!avciclass="token operator">->drainingclass="token punctuation">) class="token punctuation">{
        class="token function">av_packet_unrefclass="token punctuation">(pktclass="token punctuation">)class="token punctuation">;
        class="token comment">// 从avci->bsf中获得AVPacket࿰c;然后设置到pkt中
        ret class="token operator">= class="token function">ff_decode_get_packetclass="token punctuation">(avctxclass="token punctuation">, pktclass="token punctuation">)class="token punctuation">;
        class="token keyword">if class="token punctuation">(ret class="token operator">< class="token number">0 class="token operator">&& ret class="token operator">!= AVERROR_EOFclass="token punctuation">)
            class="token keyword">return retclass="token punctuation">;
    class="token punctuation">}

    class="token comment">// Some codecs (at least wma lossless) will crash when feeding drain packets
    class="token comment">// after EOF was signaled.
    class="token keyword">if class="token punctuation">(avciclass="token operator">->draining_doneclass="token punctuation">)
        class="token keyword">return AVERROR_EOFclass="token punctuation">;

    class="token keyword">if class="token punctuation">(class="token operator">!pktclass="token operator">->data class="token operator">&&
        class="token operator">!class="token punctuation">(avctxclass="token operator">->codecclass="token operator">->capabilities class="token operator">& AV_CODEC_CAP_DELAY class="token operator">||
          avctxclass="token operator">->active_thread_type class="token operator">& FF_THREAD_FRAMEclass="token punctuation">)class="token punctuation">)
        class="token keyword">return AVERROR_EOFclass="token punctuation">;

    got_frame class="token operator">= class="token number">0class="token punctuation">;

	class="token comment">// 多线程解码 或者 单线程
    class="token keyword">if class="token punctuation">(HAVE_THREADS class="token operator">&& avctxclass="token operator">->active_thread_type class="token operator">& FF_THREAD_FRAMEclass="token punctuation">) class="token punctuation">{
    	class="token comment">// 多线程解码
    	class="token comment">// 先调用avcodec_open2打开多个解码线程࿰c;然后这里实现多线程解码
        ret class="token operator">= class="token function">ff_thread_decode_frameclass="token punctuation">(avctxclass="token punctuation">, frameclass="token punctuation">, class="token operator">&got_frameclass="token punctuation">, pktclass="token punctuation">)class="token punctuation">;
    class="token punctuation">} class="token keyword">else class="token punctuation">{
    	class="token comment">//调用对应AVCodec的decode方法࿰c;h264默认解码器的话࿰c;就会调用class="tags" href="/tags/FFMPEG.html" title=ffmpeg>ffmpeg内置的h264解码器
        ret class="token operator">= avctxclass="token operator">->codecclass="token operator">->class="token function">decodeclass="token punctuation">(avctxclass="token punctuation">, frameclass="token punctuation">, class="token operator">&got_frameclass="token punctuation">, pktclass="token punctuation">)class="token punctuation">;

        class="token keyword">if class="token punctuation">(class="token operator">!class="token punctuation">(avctxclass="token operator">->codecclass="token operator">->caps_internal class="token operator">& FF_CODEC_CAP_SETS_PKT_DTSclass="token punctuation">)class="token punctuation">)
            frameclass="token operator">->pkt_dts class="token operator">= pktclass="token operator">->dtsclass="token punctuation">;
        class="token keyword">if class="token punctuation">(avctxclass="token operator">->codecclass="token operator">->type class="token operator">== AVMEDIA_TYPE_VIDEOclass="token punctuation">) class="token punctuation">{
            class="token keyword">ifclass="token punctuation">(class="token operator">!avctxclass="token operator">->has_b_framesclass="token punctuation">)
                frameclass="token operator">->pkt_pos class="token operator">= pktclass="token operator">->posclass="token punctuation">;
            class="token comment">//FIXME these should be under if(!avctx->has_b_frames)
            class="token comment">/* get_buffer is supposed to set frame parameters */
            class="token keyword">if class="token punctuation">(class="token operator">!class="token punctuation">(avctxclass="token operator">->codecclass="token operator">->capabilities class="token operator">& AV_CODEC_CAP_DR1class="token punctuation">)class="token punctuation">) class="token punctuation">{
                class="token keyword">if class="token punctuation">(class="token operator">!frameclass="token operator">->sample_aspect_ratioclass="token punctuation">.numclass="token punctuation">)  frameclass="token operator">->sample_aspect_ratio class="token operator">= avctxclass="token operator">->sample_aspect_ratioclass="token punctuation">;
                class="token keyword">if class="token punctuation">(class="token operator">!frameclass="token operator">->widthclass="token punctuation">)                    frameclass="token operator">->width               class="token operator">= avctxclass="token operator">->widthclass="token punctuation">;
                class="token keyword">if class="token punctuation">(class="token operator">!frameclass="token operator">->heightclass="token punctuation">)                   frameclass="token operator">->height              class="token operator">= avctxclass="token operator">->heightclass="token punctuation">;
                class="token keyword">if class="token punctuation">(frameclass="token operator">->format class="token operator">== AV_PIX_FMT_NONEclass="token punctuation">) frameclass="token operator">->format              class="token operator">= avctxclass="token operator">->pix_fmtclass="token punctuation">;
            class="token punctuation">}
        class="token punctuation">}
    class="token punctuation">}
    class="token function">emms_cclass="token punctuation">(class="token punctuation">)class="token punctuation">;
    actual_got_frame class="token operator">= got_frameclass="token punctuation">;

    class="token keyword">if class="token punctuation">(avctxclass="token operator">->codecclass="token operator">->type class="token operator">== AVMEDIA_TYPE_VIDEOclass="token punctuation">) class="token punctuation">{
    	class="token comment">//discard 丢弃掉了
        class="token keyword">if class="token punctuation">(frameclass="token operator">->flags class="token operator">& AV_FRAME_FLAG_DISCARDclass="token punctuation">)
            got_frame class="token operator">= class="token number">0class="token punctuation">;
    class="token punctuation">} class="token keyword">else class="token keyword">if class="token punctuation">(avctxclass="token operator">->codecclass="token operator">->type class="token operator">== AVMEDIA_TYPE_AUDIOclass="token punctuation">) class="token punctuation">{
        class="token class-name">uint8_t class="token operator">*sideclass="token punctuation">;
        class="token class-name">buffer_size_t side_sizeclass="token punctuation">;
        class="token class-name">uint32_t discard_padding class="token operator">= class="token number">0class="token punctuation">;
        class="token class-name">uint8_t skip_reason class="token operator">= class="token number">0class="token punctuation">;
        class="token class-name">uint8_t discard_reason class="token operator">= class="token number">0class="token punctuation">;

		class="token comment">//设置frame的一些参数
        class="token keyword">if class="token punctuation">(ret class="token operator">>= class="token number">0 class="token operator">&& got_frameclass="token punctuation">) class="token punctuation">{
            class="token keyword">if class="token punctuation">(frameclass="token operator">->format class="token operator">== AV_SAMPLE_FMT_NONEclass="token punctuation">)
                frameclass="token operator">->format class="token operator">= avctxclass="token operator">->sample_fmtclass="token punctuation">;
            class="token keyword">if class="token punctuation">(class="token operator">!frameclass="token operator">->channel_layoutclass="token punctuation">)
                frameclass="token operator">->channel_layout class="token operator">= avctxclass="token operator">->channel_layoutclass="token punctuation">;
            class="token keyword">if class="token punctuation">(class="token operator">!frameclass="token operator">->channelsclass="token punctuation">)
                frameclass="token operator">->channels class="token operator">= avctxclass="token operator">->channelsclass="token punctuation">;
            class="token keyword">if class="token punctuation">(class="token operator">!frameclass="token operator">->sample_rateclass="token punctuation">)
                frameclass="token operator">->sample_rate class="token operator">= avctxclass="token operator">->sample_rateclass="token punctuation">;
        class="token punctuation">}

        sideclass="token operator">= class="token function">av_packet_get_side_dataclass="token punctuation">(avciclass="token operator">->last_pkt_propsclass="token punctuation">, AV_PKT_DATA_SKIP_SAMPLESclass="token punctuation">, class="token operator">&side_sizeclass="token punctuation">)class="token punctuation">;
        class="token comment">//跳过skip_samples帧数
        class="token keyword">ifclass="token punctuation">(side class="token operator">&& side_sizeclass="token operator">>=class="token number">10class="token punctuation">) class="token punctuation">{
            avciclass="token operator">->skip_samples class="token operator">= class="token function">AV_RL32class="token punctuation">(sideclass="token punctuation">) class="token operator">* avciclass="token operator">->skip_samples_multiplierclass="token punctuation">;
            discard_padding class="token operator">= class="token function">AV_RL32class="token punctuation">(side class="token operator">+ class="token number">4class="token punctuation">)class="token punctuation">;
            class="token function">av_logclass="token punctuation">(avctxclass="token punctuation">, AV_LOG_DEBUGclass="token punctuation">, class="token string">"skip %d / discard %d samples due to side data\n"class="token punctuation">,
                   avciclass="token operator">->skip_samplesclass="token punctuation">, class="token punctuation">(class="token keyword">intclass="token punctuation">)discard_paddingclass="token punctuation">)class="token punctuation">;
            skip_reason class="token operator">= class="token function">AV_RL8class="token punctuation">(side class="token operator">+ class="token number">8class="token punctuation">)class="token punctuation">;
            discard_reason class="token operator">= class="token function">AV_RL8class="token punctuation">(side class="token operator">+ class="token number">9class="token punctuation">)class="token punctuation">;
        class="token punctuation">}

        class="token keyword">if class="token punctuation">(class="token punctuation">(frameclass="token operator">->flags class="token operator">& AV_FRAME_FLAG_DISCARDclass="token punctuation">) class="token operator">&& got_frame class="token operator">&&
            class="token operator">!class="token punctuation">(avctxclass="token operator">->flags2 class="token operator">& AV_CODEC_FLAG2_SKIP_MANUALclass="token punctuation">)class="token punctuation">) class="token punctuation">{
            avciclass="token operator">->skip_samples class="token operator">= class="token function">FFMAXclass="token punctuation">(class="token number">0class="token punctuation">, avciclass="token operator">->skip_samples class="token operator">- frameclass="token operator">->nb_samplesclass="token punctuation">)class="token punctuation">;
            got_frame class="token operator">= class="token number">0class="token punctuation">;
            class="token operator">*discarded_samples class="token operator">+= frameclass="token operator">->nb_samplesclass="token punctuation">;
        class="token punctuation">}

        class="token keyword">if class="token punctuation">(avciclass="token operator">->skip_samples class="token operator">> class="token number">0 class="token operator">&& got_frame class="token operator">&&
            class="token operator">!class="token punctuation">(avctxclass="token operator">->flags2 class="token operator">& AV_CODEC_FLAG2_SKIP_MANUALclass="token punctuation">)class="token punctuation">) class="token punctuation">{
            class="token keyword">ifclass="token punctuation">(frameclass="token operator">->nb_samples class="token operator"><= avciclass="token operator">->skip_samplesclass="token punctuation">)class="token punctuation">{
                got_frame class="token operator">= class="token number">0class="token punctuation">;
                class="token operator">*discarded_samples class="token operator">+= frameclass="token operator">->nb_samplesclass="token punctuation">;
                avciclass="token operator">->skip_samples class="token operator">-= frameclass="token operator">->nb_samplesclass="token punctuation">;
                class="token function">av_logclass="token punctuation">(avctxclass="token punctuation">, AV_LOG_DEBUGclass="token punctuation">, class="token string">"skip whole frame, skip left: %d\n"class="token punctuation">,
                       avciclass="token operator">->skip_samplesclass="token punctuation">)class="token punctuation">;
            class="token punctuation">} class="token keyword">else class="token punctuation">{
                class="token function">av_samples_copyclass="token punctuation">(frameclass="token operator">->extended_dataclass="token punctuation">, frameclass="token operator">->extended_dataclass="token punctuation">, class="token number">0class="token punctuation">, avciclass="token operator">->skip_samplesclass="token punctuation">,
                                frameclass="token operator">->nb_samples class="token operator">- avciclass="token operator">->skip_samplesclass="token punctuation">, avctxclass="token operator">->channelsclass="token punctuation">, frameclass="token operator">->formatclass="token punctuation">)class="token punctuation">;
                class="token keyword">ifclass="token punctuation">(avctxclass="token operator">->pkt_timebaseclass="token punctuation">.num class="token operator">&& avctxclass="token operator">->sample_rateclass="token punctuation">) class="token punctuation">{
                    class="token class-name">int64_t diff_ts class="token operator">= class="token function">av_rescale_qclass="token punctuation">(avciclass="token operator">->skip_samplesclass="token punctuation">,
                                                   class="token punctuation">(AVRationalclass="token punctuation">)class="token punctuation">{class="token number">1class="token punctuation">, avctxclass="token operator">->sample_rateclass="token punctuation">}class="token punctuation">,
                                                   avctxclass="token operator">->pkt_timebaseclass="token punctuation">)class="token punctuation">;
                    class="token keyword">ifclass="token punctuation">(frameclass="token operator">->ptsclass="token operator">!=AV_NOPTS_VALUEclass="token punctuation">)
                        frameclass="token operator">->pts class="token operator">+= diff_tsclass="token punctuation">;
class="token macro property">class="token directive-hash">#class="token directive keyword">if class="token expression">FF_API_PKT_PTS
FF_DISABLE_DEPRECATION_WARNINGS
                    class="token keyword">ifclass="token punctuation">(frameclass="token operator">->pkt_ptsclass="token operator">!=AV_NOPTS_VALUEclass="token punctuation">)
                        frameclass="token operator">->pkt_pts class="token operator">+= diff_tsclass="token punctuation">;
FF_ENABLE_DEPRECATION_WARNINGS
class="token macro property">class="token directive-hash">#class="token directive keyword">endif
                    class="token keyword">ifclass="token punctuation">(frameclass="token operator">->pkt_dtsclass="token operator">!=AV_NOPTS_VALUEclass="token punctuation">)
                        frameclass="token operator">->pkt_dts class="token operator">+= diff_tsclass="token punctuation">;
                    class="token keyword">if class="token punctuation">(frameclass="token operator">->pkt_duration class="token operator">>= diff_tsclass="token punctuation">)
                        frameclass="token operator">->pkt_duration class="token operator">-= diff_tsclass="token punctuation">;
                class="token punctuation">} class="token keyword">else class="token punctuation">{
                    class="token function">av_logclass="token punctuation">(avctxclass="token punctuation">, AV_LOG_WARNINGclass="token punctuation">, class="token string">"Could not update timestamps for skipped samples.\n"class="token punctuation">)class="token punctuation">;
                class="token punctuation">}
                class="token function">av_logclass="token punctuation">(avctxclass="token punctuation">, AV_LOG_DEBUGclass="token punctuation">, class="token string">"skip %d/%d samples\n"class="token punctuation">,
                       avciclass="token operator">->skip_samplesclass="token punctuation">, frameclass="token operator">->nb_samplesclass="token punctuation">)class="token punctuation">;
                class="token operator">*discarded_samples class="token operator">+= avciclass="token operator">->skip_samplesclass="token punctuation">;
                frameclass="token operator">->nb_samples class="token operator">-= avciclass="token operator">->skip_samplesclass="token punctuation">;
                avciclass="token operator">->skip_samples class="token operator">= class="token number">0class="token punctuation">;
            class="token punctuation">}
        class="token punctuation">}

        class="token keyword">if class="token punctuation">(discard_padding class="token operator">> class="token number">0 class="token operator">&& discard_padding class="token operator"><= frameclass="token operator">->nb_samples class="token operator">&& got_frame class="token operator">&&
            class="token operator">!class="token punctuation">(avctxclass="token operator">->flags2 class="token operator">& AV_CODEC_FLAG2_SKIP_MANUALclass="token punctuation">)class="token punctuation">) class="token punctuation">{
            class="token keyword">if class="token punctuation">(discard_padding class="token operator">== frameclass="token operator">->nb_samplesclass="token punctuation">) class="token punctuation">{
                class="token operator">*discarded_samples class="token operator">+= frameclass="token operator">->nb_samplesclass="token punctuation">;
                got_frame class="token operator">= class="token number">0class="token punctuation">;
            class="token punctuation">} class="token keyword">else class="token punctuation">{
                class="token keyword">ifclass="token punctuation">(avctxclass="token operator">->pkt_timebaseclass="token punctuation">.num class="token operator">&& avctxclass="token operator">->sample_rateclass="token punctuation">) class="token punctuation">{
                    class="token class-name">int64_t diff_ts class="token operator">= class="token function">av_rescale_qclass="token punctuation">(frameclass="token operator">->nb_samples class="token operator">- discard_paddingclass="token punctuation">,
                                                   class="token punctuation">(AVRationalclass="token punctuation">)class="token punctuation">{class="token number">1class="token punctuation">, avctxclass="token operator">->sample_rateclass="token punctuation">}class="token punctuation">,
                                                   avctxclass="token operator">->pkt_timebaseclass="token punctuation">)class="token punctuation">;
                    frameclass="token operator">->pkt_duration class="token operator">= diff_tsclass="token punctuation">;
                class="token punctuation">} class="token keyword">else class="token punctuation">{
                    class="token function">av_logclass="token punctuation">(avctxclass="token punctuation">, AV_LOG_WARNINGclass="token punctuation">, class="token string">"Could not update timestamps for discarded samples.\n"class="token punctuation">)class="token punctuation">;
                class="token punctuation">}
                class="token function">av_logclass="token punctuation">(avctxclass="token punctuation">, AV_LOG_DEBUGclass="token punctuation">, class="token string">"discard %d/%d samples\n"class="token punctuation">,
                       class="token punctuation">(class="token keyword">intclass="token punctuation">)discard_paddingclass="token punctuation">, frameclass="token operator">->nb_samplesclass="token punctuation">)class="token punctuation">;
                frameclass="token operator">->nb_samples class="token operator">-= discard_paddingclass="token punctuation">;
            class="token punctuation">}
        class="token punctuation">}

        class="token keyword">if class="token punctuation">(class="token punctuation">(avctxclass="token operator">->flags2 class="token operator">& AV_CODEC_FLAG2_SKIP_MANUALclass="token punctuation">) class="token operator">&& got_frameclass="token punctuation">) class="token punctuation">{
            AVFrameSideData class="token operator">*fside class="token operator">= class="token function">av_frame_new_side_dataclass="token punctuation">(frameclass="token punctuation">, AV_FRAME_DATA_SKIP_SAMPLESclass="token punctuation">, class="token number">10class="token punctuation">)class="token punctuation">;
            class="token keyword">if class="token punctuation">(fsideclass="token punctuation">) class="token punctuation">{
                class="token function">AV_WL32class="token punctuation">(fsideclass="token operator">->dataclass="token punctuation">, avciclass="token operator">->skip_samplesclass="token punctuation">)class="token punctuation">;
                class="token function">AV_WL32class="token punctuation">(fsideclass="token operator">->data class="token operator">+ class="token number">4class="token punctuation">, discard_paddingclass="token punctuation">)class="token punctuation">;
                class="token function">AV_WL8class="token punctuation">(fsideclass="token operator">->data class="token operator">+ class="token number">8class="token punctuation">, skip_reasonclass="token punctuation">)class="token punctuation">;
                class="token function">AV_WL8class="token punctuation">(fsideclass="token operator">->data class="token operator">+ class="token number">9class="token punctuation">, discard_reasonclass="token punctuation">)class="token punctuation">;
                avciclass="token operator">->skip_samples class="token operator">= class="token number">0class="token punctuation">;
            class="token punctuation">}
        class="token punctuation">}
    class="token punctuation">}

    class="token keyword">if class="token punctuation">(avctxclass="token operator">->codecclass="token operator">->type class="token operator">== AVMEDIA_TYPE_AUDIO class="token operator">&&
        class="token operator">!avciclass="token operator">->showed_multi_packet_warning class="token operator">&&
        ret class="token operator">>= class="token number">0 class="token operator">&& ret class="token operator">!= pktclass="token operator">->size class="token operator">&& class="token operator">!class="token punctuation">(avctxclass="token operator">->codecclass="token operator">->capabilities class="token operator">& AV_CODEC_CAP_SUBFRAMESclass="token punctuation">)class="token punctuation">) class="token punctuation">{
        class="token function">av_logclass="token punctuation">(avctxclass="token punctuation">, AV_LOG_WARNINGclass="token punctuation">, class="token string">"Multiple frames in a packet.\n"class="token punctuation">)class="token punctuation">;
        avciclass="token operator">->showed_multi_packet_warning class="token operator">= class="token number">1class="token punctuation">;
    class="token punctuation">}

    class="token keyword">if class="token punctuation">(class="token operator">!got_frameclass="token punctuation">)
        class="token function">av_frame_unrefclass="token punctuation">(frameclass="token punctuation">)class="token punctuation">;

    class="token keyword">if class="token punctuation">(ret class="token operator">>= class="token number">0 class="token operator">&& avctxclass="token operator">->codecclass="token operator">->type class="token operator">== AVMEDIA_TYPE_VIDEO class="token operator">&& class="token operator">!class="token punctuation">(avctxclass="token operator">->flags class="token operator">& AV_CODEC_FLAG_TRUNCATEDclass="token punctuation">)class="token punctuation">)
        ret class="token operator">= pktclass="token operator">->sizeclass="token punctuation">;

class="token macro property">class="token directive-hash">#class="token directive keyword">if class="token expression">FF_API_AVCTX_TIMEBASE
    class="token keyword">if class="token punctuation">(avctxclass="token operator">->framerateclass="token punctuation">.num class="token operator">> class="token number">0 class="token operator">&& avctxclass="token operator">->framerateclass="token punctuation">.den class="token operator">> class="token number">0class="token punctuation">)
        avctxclass="token operator">->time_base class="token operator">= class="token function">av_inv_qclass="token punctuation">(class="token function">av_mul_qclass="token punctuation">(avctxclass="token operator">->framerateclass="token punctuation">, class="token punctuation">(AVRationalclass="token punctuation">)class="token punctuation">{avctxclass="token operator">->ticks_per_frameclass="token punctuation">, class="token number">1class="token punctuation">}class="token punctuation">)class="token punctuation">)class="token punctuation">;
class="token macro property">class="token directive-hash">#class="token directive keyword">endif

    class="token comment">/* do not stop draining when actual_got_frame != 0 or ret < 0 */
    class="token comment">/* got_frame == 0 but actual_got_frame != 0 when frame is discarded */
    class="token keyword">if class="token punctuation">(avciclass="token operator">->draining class="token operator">&& class="token operator">!actual_got_frameclass="token punctuation">) class="token punctuation">{
        class="token keyword">if class="token punctuation">(ret class="token operator">< class="token number">0class="token punctuation">) class="token punctuation">{
            class="token comment">/* prevent infinite loop if a decoder wrongly always return error on draining */
            class="token comment">/* reasonable nb_errors_max = maximum b frames + thread count */
            class="token keyword">int nb_errors_max class="token operator">= class="token number">20 class="token operator">+ class="token punctuation">(HAVE_THREADS class="token operator">&& avctxclass="token operator">->active_thread_type class="token operator">& FF_THREAD_FRAME class="token operator">?
                                avctxclass="token operator">->thread_count class="token operator">: class="token number">1class="token punctuation">)class="token punctuation">;

            class="token keyword">if class="token punctuation">(avciclass="token operator">->nb_draining_errorsclass="token operator">++ class="token operator">>= nb_errors_maxclass="token punctuation">) class="token punctuation">{
                class="token function">av_logclass="token punctuation">(avctxclass="token punctuation">, AV_LOG_ERRORclass="token punctuation">, class="token string">"Too many errors when draining, this is a bug. "
                       class="token string">"Stop draining and force EOF.\n"class="token punctuation">)class="token punctuation">;
                avciclass="token operator">->draining_done class="token operator">= class="token number">1class="token punctuation">;
                ret class="token operator">= AVERROR_BUGclass="token punctuation">;
            class="token punctuation">}
        class="token punctuation">} class="token keyword">else class="token punctuation">{
            avciclass="token operator">->draining_done class="token operator">= class="token number">1class="token punctuation">;
        class="token punctuation">}
    class="token punctuation">}

class="token macro property">class="token directive-hash">#class="token directive keyword">if class="token expression">FF_API_OLD_ENCDEC
    avciclass="token operator">->compat_decode_consumed class="token operator">+= retclass="token punctuation">;
class="token macro property">class="token directive-hash">#class="token directive keyword">endif

    class="token keyword">if class="token punctuation">(ret class="token operator">>= pktclass="token operator">->size class="token operator">|| ret class="token operator">< class="token number">0class="token punctuation">) class="token punctuation">{
        class="token function">av_packet_unrefclass="token punctuation">(pktclass="token punctuation">)class="token punctuation">;
        class="token function">av_packet_unrefclass="token punctuation">(avciclass="token operator">->last_pkt_propsclass="token punctuation">)class="token punctuation">;
    class="token punctuation">} class="token keyword">else class="token punctuation">{
        class="token keyword">int consumed class="token operator">= retclass="token punctuation">;

        pktclass="token operator">->data                class="token operator">+= consumedclass="token punctuation">;
        pktclass="token operator">->size                class="token operator">-= consumedclass="token punctuation">;
        avciclass="token operator">->last_pkt_propsclass="token operator">->size class="token operator">-= consumedclass="token punctuation">; class="token comment">// See extract_packet_props() comment.
        pktclass="token operator">->pts                  class="token operator">= AV_NOPTS_VALUEclass="token punctuation">;
        pktclass="token operator">->dts                  class="token operator">= AV_NOPTS_VALUEclass="token punctuation">;
        avciclass="token operator">->last_pkt_propsclass="token operator">->pts class="token operator">= AV_NOPTS_VALUEclass="token punctuation">;
        avciclass="token operator">->last_pkt_propsclass="token operator">->dts class="token operator">= AV_NOPTS_VALUEclass="token punctuation">;
    class="token punctuation">}

    class="token keyword">if class="token punctuation">(got_frameclass="token punctuation">)
        class="token function">av_assert0class="token punctuation">(frameclass="token operator">->bufclass="token punctuation">[class="token number">0class="token punctuation">]class="token punctuation">)class="token punctuation">;

    class="token keyword">return ret class="token operator">< class="token number">0 class="token operator">? ret class="token operator">: class="token number">0class="token punctuation">;
class="token punctuation">}

code>

code_frame__494">ff_thread_decode_frame 源码

多线程解码实现࿰c;在此之前࿰c;通过需要先通过调用avcodec_open2创建多个线程。
然后在这个函数中࿰c;先调用submit_packet()函数提交packet到下一个解码线程࿰c;然后调用数组中最前面线程进行解码。相关代码如下：

<code class="prism language-c">class="token keyword">int class="token function">ff_thread_decode_frameclass="token punctuation">(AVCodecContext class="token operator">*avctxclass="token punctuation">,
                           AVFrame class="token operator">*pictureclass="token punctuation">, class="token keyword">int class="token operator">*got_picture_ptrclass="token punctuation">,
                           AVPacket class="token operator">*avpktclass="token punctuation">)
class="token punctuation">{
    FrameThreadContext class="token operator">*fctx class="token operator">= avctxclass="token operator">->internalclass="token operator">->thread_ctxclass="token punctuation">;
    class="token keyword">int finished class="token operator">= fctxclass="token operator">->next_finishedclass="token punctuation">;
    PerThreadContext class="token operator">*pclass="token punctuation">;
    class="token keyword">int errclass="token punctuation">;

    class="token comment">/* release the async lock, permitting blocked hwaccel threads to
     * go forward while we are in this function */
    class="token function">async_unlockclass="token punctuation">(fctxclass="token punctuation">)class="token punctuation">;

    class="token comment">/*
     * Submit a packet to the next decoding thread.
     */

    p class="token operator">= class="token operator">&fctxclass="token operator">->threadsclass="token punctuation">[fctxclass="token operator">->next_decodingclass="token punctuation">]class="token punctuation">;
    class="token comment">// PerThreadContext是对应线程的上下文࿰c;这是在调用avcodec_open2时候创建的。
    class="token comment">// 这里是把avpkt转移到p->avpkt࿰c;然后触发PerThreadContext的input_cond信号量࿰c;告诉对应的解码线程࿰c;可以开始解码了。
    class="token comment">// 具体的解码实现在pthread_frame.c文件中的frame_worker_thread函数。
    err class="token operator">= class="token function">submit_packetclass="token punctuation">(pclass="token punctuation">, avctxclass="token punctuation">, avpktclass="token punctuation">)class="token punctuation">;
    class="token keyword">if class="token punctuation">(errclass="token punctuation">)
        class="token keyword">goto finishclass="token punctuation">;

    class="token comment">/*
     * If we're still receiving the initial packets, don't return a frame.
     */

    class="token keyword">if class="token punctuation">(fctxclass="token operator">->next_decoding class="token operator">> class="token punctuation">(avctxclass="token operator">->thread_countclass="token operator">-class="token number">1class="token operator">-class="token punctuation">(avctxclass="token operator">->codec_id class="token operator">== AV_CODEC_ID_FFV1class="token punctuation">)class="token punctuation">)class="token punctuation">)
        fctxclass="token operator">->delaying class="token operator">= class="token number">0class="token punctuation">;

    class="token keyword">if class="token punctuation">(fctxclass="token operator">->delayingclass="token punctuation">) class="token punctuation">{
        class="token operator">*got_picture_ptrclass="token operator">=class="token number">0class="token punctuation">;
        class="token keyword">if class="token punctuation">(avpktclass="token operator">->sizeclass="token punctuation">) class="token punctuation">{
            err class="token operator">= avpktclass="token operator">->sizeclass="token punctuation">;
            class="token keyword">goto finishclass="token punctuation">;
        class="token punctuation">}
    class="token punctuation">}

    class="token comment">/*
     * Return the next available frame from the oldest thread.
     * If we're at the end of the stream, then we have to skip threads that
     * didn't output a frame/error, because we don't want to accidentally signal
     * EOF (avpkt->size == 0 && *got_picture_ptr == 0 && err >= 0).
     */

    class="token keyword">do class="token punctuation">{
        p class="token operator">= class="token operator">&fctxclass="token operator">->threadsclass="token punctuation">[finishedclass="token operator">++class="token punctuation">]class="token punctuation">;
		class="token comment">//上面通过调用submit_packet提交AVPacket给解码线程后࿰c;这里就等待output_cond完成
        class="token keyword">if class="token punctuation">(class="token function">atomic_loadclass="token punctuation">(class="token operator">&pclass="token operator">->stateclass="token punctuation">) class="token operator">!= STATE_INPUT_READYclass="token punctuation">) class="token punctuation">{
            class="token function">pthread_mutex_lockclass="token punctuation">(class="token operator">&pclass="token operator">->progress_mutexclass="token punctuation">)class="token punctuation">;
            class="token keyword">while class="token punctuation">(class="token function">atomic_load_explicitclass="token punctuation">(class="token operator">&pclass="token operator">->stateclass="token punctuation">, memory_order_relaxedclass="token punctuation">) class="token operator">!= STATE_INPUT_READYclass="token punctuation">)
                class="token function">pthread_cond_waitclass="token punctuation">(class="token operator">&pclass="token operator">->output_condclass="token punctuation">, class="token operator">&pclass="token operator">->progress_mutexclass="token punctuation">)class="token punctuation">;
            class="token function">pthread_mutex_unlockclass="token punctuation">(class="token operator">&pclass="token operator">->progress_mutexclass="token punctuation">)class="token punctuation">;
        class="token punctuation">}
		class="token comment">//获取解码后的frame࿰c;然后把frame给到picture。
        class="token function">av_frame_move_refclass="token punctuation">(pictureclass="token punctuation">, pclass="token operator">->frameclass="token punctuation">)class="token punctuation">;
        class="token operator">*got_picture_ptr class="token operator">= pclass="token operator">->got_frameclass="token punctuation">;
        pictureclass="token operator">->pkt_dts class="token operator">= pclass="token operator">->avpktclass="token operator">->dtsclass="token punctuation">;
        err class="token operator">= pclass="token operator">->resultclass="token punctuation">;

        class="token comment">/*
         * A later call with avkpt->size == 0 may loop over all threads,
         * including this one, searching for a frame/error to return before being
         * stopped by the "finished != fctx->next_finished" condition.
         * Make sure we don't mistakenly return the same frame/error again.
         */
        pclass="token operator">->got_frame class="token operator">= class="token number">0class="token punctuation">;
        pclass="token operator">->result class="token operator">= class="token number">0class="token punctuation">;

        class="token keyword">if class="token punctuation">(finished class="token operator">>= avctxclass="token operator">->thread_countclass="token punctuation">) finished class="token operator">= class="token number">0class="token punctuation">;
    class="token punctuation">} class="token keyword">while class="token punctuation">(class="token operator">!avpktclass="token operator">->size class="token operator">&& class="token operator">!class="token operator">*got_picture_ptr class="token operator">&& err class="token operator">>= class="token number">0 class="token operator">&& finished class="token operator">!= fctxclass="token operator">->next_finishedclass="token punctuation">)class="token punctuation">;

    class="token function">update_context_from_threadclass="token punctuation">(avctxclass="token punctuation">, pclass="token operator">->avctxclass="token punctuation">, class="token number">1class="token punctuation">)class="token punctuation">;

    class="token keyword">if class="token punctuation">(fctxclass="token operator">->next_decoding class="token operator">>= avctxclass="token operator">->thread_countclass="token punctuation">) fctxclass="token operator">->next_decoding class="token operator">= class="token number">0class="token punctuation">;

    fctxclass="token operator">->next_finished class="token operator">= finishedclass="token punctuation">;

    class="token comment">/* return the size of the consumed packet if no error occurred */
    class="token keyword">if class="token punctuation">(err class="token operator">>= class="token number">0class="token punctuation">)
        err class="token operator">= avpktclass="token operator">->sizeclass="token punctuation">;
finishclass="token operator">:
    class="token function">async_lockclass="token punctuation">(fctxclass="token punctuation">)class="token punctuation">;
    class="token keyword">return errclass="token punctuation">;
class="token punctuation">}

code>