ffmpeg mp4转h264 cpp代码

以下是使用 FFmpeg 将 MP4 文件转换为 H.264 编码的 CPP 代码示例：

extern "C"
{
#include <libavformat/avformat.h>
#include <libavcodec/avcodec.h>
#include <libswscale/swscale.h>
}

int main(int argc, char *argv[])
{
    AVFormatContext *pFormatCtx = NULL;
    AVCodecContext *pCodecCtxOrig = NULL, *pCodecCtx = NULL;
    AVCodec *pCodec = NULL;
    AVFrame *pFrame = NULL;
    AVPacket packet;
    int i, videoStream;
    struct SwsContext *sws_ctx = NULL;

    // Open the input file
    if (avformat_open_input(&pFormatCtx, argv[1], NULL, NULL) != 0)
        return -1;

    // Retrieve stream information
    if (avformat_find_stream_info(pFormatCtx, NULL) < 0)
        return -1;

    // Find the first video stream
    videoStream = -1;
    for (i = 0; i < pFormatCtx->nb_streams; i++)
        if (pFormatCtx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO)
        {
            videoStream = i;
            break;
        }
    if (videoStream == -1)
        return -1;

    // Get a pointer to the codec context for the video stream
    pCodecCtxOrig = pFormatCtx->streams[videoStream]->codec;
    pCodec = avcodec_find_decoder(pCodecCtxOrig->codec_id);
    if (pCodec == NULL)
        return -1;

    // Copy context
    pCodecCtx = avcodec_alloc_context3(pCodec);
    if (avcodec_copy_context(pCodecCtx, pCodecCtxOrig) != 0)
        return -1;

    // Open codec
    if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0)
        return -1;

    // Allocate video frame
    pFrame = av_frame_alloc();
    if (pFrame == NULL)
        return -1;

    // Read frames and save to file
    while (av_read_frame(pFormatCtx, &packet) >= 0)
    {
        // Is this a packet from the video stream?
        if (packet.stream_index == videoStream)
        {
            // Decode video frame
            int ret = avcodec_send_packet(pCodecCtx, &packet);
            if (ret < 0)
                break;
            while (ret >= 0)
            {
                ret = avcodec_receive_frame(pCodecCtx, pFrame);
                if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
                    break;
                else if (ret < 0)
                    break;

                // Convert the image from its native format to RGB
                sws_ctx = sws_getCachedContext(sws_ctx, pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt,
                                               pCodecCtx->width, pCodecCtx->height, AV_PIX_FMT_BGR24, SWS_BICUBIC, NULL, NULL, NULL);
                if (!sws_ctx)
                    return -1;
                uint8_t *buffer = (uint8_t *)malloc(pCodecCtx->width * pCodecCtx->height * 3);
                if (!buffer)
                    return -1;
                uint8_t *pBuffer[1] = {buffer};
                int linesize[1] = {3 * pCodecCtx->width};
                int h = sws_scale(sws_ctx, (uint8_t const *const *)pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pBuffer, linesize);
                if (h > 0)
                {
                    // Write the RGB image to file
                    FILE *fp = fopen("output.rgb", "ab");
                    if (fp != NULL)
                    {
                        fwrite(buffer, 1, pCodecCtx->width * pCodecCtx->height * 3, fp);
                        fclose(fp);
                    }
                }
                free(buffer);
            }
        }

        // Free the packet that was allocated by av_read_frame
        av_packet_unref(&packet);
    }

    // Free the RGB image
    sws_freeContext(sws_ctx);

    // Free the YUV frame
    av_frame_free(&pFrame);

    // Close the codec
    avcodec_close(pCodecCtx);

    // Close the video file
    avformat_close_input(&pFormatCtx);

    return 0;
}

这段代码将 MP4 文件中的 H.264 视频帧解码为 YUV 格式，然后将其转换为 RGB 格式并写入到文件中。你可以根据实际需求进行修改。