AVFilterPad起一个输入和输出接口的作用

结构体

/**
 * A filter pad used for either input or output.
 */
struct AVFilterPad {
    /**
     * Pad name. The name is unique among inputs and among outputs, but an
     * input may have the same name as an output. This may be NULL if this
     * pad has no need to ever be referenced by name.
     */
    const char *name;

    /**
     * AVFilterPad type.
     */
    enum AVMediaType type;

    /**
     * The filter expects writable frames from its input link,
     * duplicating data buffers if needed.
     *
     * input pads only.
     */
#define AVFILTERPAD_FLAG_NEEDS_WRITABLE                  (1 << 0)

    /**
     * The pad's name is allocated and should be freed generically.
     */
#define AVFILTERPAD_FLAG_FREE_NAME                       (1 << 1)

    /**
     * A combination of AVFILTERPAD_FLAG_* flags.
     */
    int flags;

    /**
     * Callback functions to get a video/audio buffers. If NULL,
     * the filter system will use ff_default_get_video_buffer() for video
     * and ff_default_get_audio_buffer() for audio.
     *
     * The state of the union is determined by type.
     *
     * Input pads only.
     */
    union {
        AVFrame *(*video)(AVFilterLink *link, int w, int h);
        AVFrame *(*audio)(AVFilterLink *link, int nb_samples);
    } get_buffer;

    /**
     * Filtering callback. This is where a filter receives a frame with
     * audio/video data and should do its processing.
     *
     * Input pads only.
     *
     * @return >= 0 on success, a negative AVERROR on error. This function
     * must ensure that frame is properly unreferenced on error if it
     * hasn't been passed on to another filter.
     */
    int (*filter_frame)(AVFilterLink *link, AVFrame *frame);

    /**
     * Frame request callback. A call to this should result in some progress
     * towards producing output over the given link. This should return zero
     * on success, and another value on error.
     *
     * Output pads only.
     */
    int (*request_frame)(AVFilterLink *link);

    /**
     * Link configuration callback.
     *
     * For output pads, this should set the link properties such as
     * width/height. This should NOT set the format property - that is
     * negotiated between filters by the filter system using the
     * query_formats() callback before this function is called.
     *
     * For input pads, this should check the properties of the link, and update
     * the filter's internal state as necessary.
     *
     * For both input and output filters, this should return zero on success,
     * and another value on error.
     */
    int (*config_props)(AVFilterLink *link);
};

函数

/**
 * Get the name of an AVFilterPad.
 *
 * @param pads an array of AVFilterPads
 * @param pad_idx index of the pad in the array; it is the caller's
 *                responsibility to ensure the index is valid
 *
 * @return name of the pad_idx'th pad in pads
 */
const char *avfilter_pad_get_name(const AVFilterPad *pads, int pad_idx);

/**
 * Get the type of an AVFilterPad.
 *
 * @param pads an array of AVFilterPads
 * @param pad_idx index of the pad in the array; it is the caller's
 *                responsibility to ensure the index is valid
 *
 * @return type of the pad_idx'th pad in pads
 */
enum AVMediaType avfilter_pad_get_type(const AVFilterPad *pads, int pad_idx);

/**
 * Append a new input/output pad to the filter's list of such pads.
 *
 * The *_free_name versions will set the AVFILTERPAD_FLAG_FREE_NAME flag
 * ensuring that the name will be freed generically (even on insertion error).
 */
int ff_append_inpad (AVFilterContext *f, AVFilterPad *p);
int ff_append_outpad(AVFilterContext *f, AVFilterPad *p);
int ff_append_inpad_free_name (AVFilterContext *f, AVFilterPad *p);
int ff_append_outpad_free_name(AVFilterContext *f, AVFilterPad *p);