要对H265文件进行编码和解码，需要使用FFmpeg库提供的相关API。以下是一个简单的C++程序，演示如何使用FFmpeg进行H265文件的编码和解码：

编码：

#include <cstdlib>
#include <cstdio>
#include <cstring>
#include <cstdint>

extern "C" {
#include <libavutil/opt.h>
#include <libavcodec/avcodec.h>
}

int main(int argc, char** argv) {
    AVCodec* codec = nullptr;
    AVCodecContext* codec_ctx = nullptr;
    AVFrame* frame = nullptr;
    AVPacket packet;
    FILE* infile, * outfile;

    avcodec_register_all();

    codec = avcodec_find_encoder_by_name("libx265");

    codec_ctx = avcodec_alloc_context3(codec);
    codec_ctx->bit_rate = 4000000;
    codec_ctx->width = 1280;
    codec_ctx->height = 720;
    codec_ctx->gop_size = 10;
    codec_ctx->max_b_frames = 1;
    codec_ctx->pix_fmt = AV_PIX_FMT_YUV420P;

    av_opt_set(codec_ctx->priv_data, "preset", "fast", 0);

    if (avcodec_open2(codec_ctx, codec, nullptr) < 0) {
        fprintf(stderr, "Could not open codec\n");
        return EXIT_FAILURE;
    }

    infile = std::fopen("input.yuv", "rb");
    if (!infile) {
        fprintf(stderr, "Could not open input file\n");
        return EXIT_FAILURE;
    }

    outfile = std::fopen("output.h265", "wb");
    if (!outfile) {
        fprintf(stderr, "Could not open output file\n");
        return EXIT_FAILURE;
    }

    frame = av_frame_alloc();
    frame->width = codec_ctx->width;
    frame->height = codec_ctx->height;
    frame->format = codec_ctx->pix_fmt;
    if (av_frame_get_buffer(frame, 32) < 0) {
        fprintf(stderr, "Could not allocate frame buffer\n");
        return EXIT_FAILURE;
    }

    int frame_size = av_image_get_buffer_size(codec_ctx->pix_fmt, codec_ctx->width, codec_ctx->height, 1);
    uint8_t* frame_buf = (uint8_t*)av_malloc(frame_size);

    while (true) {
        int ret = fread(frame_buf, 1, frame_size, infile);
        if (ret < frame_size) {
            break;
        }

        av_frame_make_writable(frame);

        uint8_t* pY = frame_buf;
        uint8_t* pU = frame_buf + frame_size / 4;
        uint8_t* pV = frame_buf + frame_size * 5 / 16;

        for (int y = 0; y < codec_ctx->height; y++) {
            memcpy(frame->data[0] + y * frame->linesize[0], pY + y * codec_ctx->width, codec_ctx->width);
        }

        for (int y = 0; y < codec_ctx->height / 2; y++) {
            memcpy(frame->data[1] + y * frame->linesize[1], pU + y * codec_ctx->width / 2, codec_ctx->width / 2);
            memcpy(frame->data[2] + y * frame->linesize[2], pV + y * codec_ctx->width / 2, codec_ctx->width / 2);
        }

        avcodec_send_frame(codec_ctx, frame);

        while (true) {
            ret = avcodec_receive_packet(codec_ctx, &packet);
            if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
                break;
            } else if (ret < 0) {
                fprintf(stderr, "Error encoding frame\n");
                return EXIT_FAILURE;
            }

            fwrite(packet.data, 1, packet.size, outfile);
            av_packet_unref(&packet);
        }
    }

    avcodec_send_frame(codec_ctx, nullptr);

    while (true) {
        int ret = avcodec_receive_packet(codec_ctx, &packet);
        if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
            break;
        } else if (ret < 0) {
            fprintf(stderr, "Error encoding frame\n");
            return EXIT_FAILURE;
        }

        fwrite(packet.data, 1, packet.size, outfile);
        av_packet_unref(&packet);
    }

    std::fclose(infile);
    std::fclose(outfile);
    av_frame_free(&frame);
    av_free(frame_buf);
    avcodec_free_context(&codec_ctx);

    return EXIT_SUCCESS;
}

解码：

#include <cstdlib>
#include <cstdio>
#include <cstring>
#include <cstdint>

extern "C" {
#include <libavcodec/avcodec.h>
#include <libavutil/frame.h>
#include <libavutil/imgutils.h>
}

int main(int argc, char** argv) {
    AVCodec* codec = nullptr;
    AVCodecContext* codec_ctx = nullptr;
    AVFrame* frame = nullptr;
    AVPacket packet;
    FILE* infile, * outfile;

    avcodec_register_all();

    codec = avcodec_find_decoder_by_name("libx265");

    codec_ctx = avcodec_alloc_context3(codec);

    if (avcodec_open2(codec_ctx, codec, nullptr) < 0) {
        fprintf(stderr, "Could not open codec\n");
        return EXIT_FAILURE;
    }

    infile = std::fopen("input.h265", "rb");
    if (!infile) {
        fprintf(stderr, "Could not open input file\n");
        return EXIT_FAILURE;
    }

    outfile = std::fopen("output.yuv", "wb");
    if (!outfile) {
        fprintf(stderr, "Could not open output file\n");
        return EXIT_FAILURE;
    }

    frame = av_frame_alloc();

    while (true) {
        int ret = av_read_frame(format_ctx, &packet);
        if (ret < 0) {
            break;
        }

        if (packet.stream_index != video_stream_idx) {
            av_packet_unref(&packet);
            continue;
        }

        avcodec_send_packet(codec_ctx, &packet);

        while (true) {
            ret = avcodec_receive_frame(codec_ctx, frame);
            if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
                break;
            } else if (ret < 0) {
                fprintf(stderr, "Error decoding frame\n");
                return EXIT_FAILURE;
            }

            uint8_t* pY = frame->data[0];
            uint8_t* pU = frame->data[1];
            uint8_t* pV = frame->data[2];

            for (int y = 0; y < codec_ctx->height; y++) {
                fwrite(pY + y * frame->linesize[0], 1, codec_ctx->width, outfile);
            }

            for (int y = 0; y < codec_ctx->height / 2; y++) {
                fwrite(pU + y * frame->linesize[1], 1, codec_ctx->width / 2, outfile);
                fwrite(pV + y * frame->linesize[2], 1, codec_ctx->width / 2, outfile);
            }

            av_frame_unref(frame);
        }

        av_packet_unref(&packet);
    }

    std::fclose(infile);
    std::fclose(outfile);
    av_frame_free(&frame);
    avcodec_free_context(&codec_ctx);

    return EXIT_SUCCESS;
}

需要注意的是，以上程序中的一些常量参数可能需要根据实际情况进行调整。