ffmpeg - .mp4 视频不播放，它是从 ffmpeg 库(不是命令行)创建的

Question

我使用 ffmpeg 库将帧编码为 .mp4 视频。该程序运行顺利，没有错误。但输出的 .mp4 视频无法播放。该文件的属性甚至没有显示它是一个视频文件，没有任何视频流信息。

相关代码为:

const char* ouVideoFileName = "output.mp4";
AVCodecID ouCodec_id = CODEC_ID_H264;

但是，如果我将其更改为:

const char* ouVideoFileName = "output.avi";
AVCodecID ouCodec_id = CODEC_ID_H264;

.avi 视频可以正常播放。

.mp4 视频有什么问题？

Answer 1

您需要共享更多代码才能找到确切的问题。通常，一旦在输出文件名中指定了容器格式，就需要使用 av_guess_format 来获取输出格式。之后，您可以使用 av_find_encoder 建议 codec_id
你需要做这样的事情

 AVFormatContext *m_outformat = NULL;
 AVOutputFormat *outfmt = NULL;
 std::string outfile = "clip_out.mp4";
 outfmt = av_guess_format(NULL,outfile.c_str(),NULL);

 if(outfmt == NULL)
 {
    ret = -1;
    return ret;
 }
 else
 {
    m_outformat = avformat_alloc_context();
    if(m_outformat)
    {
       m_outformat->oformat = outfmt;
       _snprintf(m_outformat->filename, sizeof(m_outformat->filename), "%s", outfile.c_str());    
    }
    else
    {
       ret = -1;
       return ret;
    }
  }

    AVCodec *out_vid_codec,*out_aud_codec;
    out_vid_codec = out_aud_codec = NULL;

    if(outfmt->video_codec != AV_CODEC_ID_NONE && m_in_vid_strm != NULL)
    {
        out_vid_codec = avcodec_find_encoder(outfmt->video_codec);
        if(NULL == out_vid_codec)
        {
            PRINT_MSG("Could Not Find Vid Encoder")
            ret = -1;
            return ret;
        }
        else
        {
            PRINT_MSG("Found Out Vid Encoder ")
            m_out_vid_strm = avformat_new_stream(m_outformat, out_vid_codec);
            if(NULL == m_out_vid_strm)
            {
                 PRINT_MSG("Failed to Allocate Output Vid Strm ")
                 ret = -1;
                 return ret;
            }
            else
            {
                 PRINT_MSG("Allocated Video Stream ")
                 if(avcodec_copy_context(m_out_vid_strm->codec, m_informat->streams[m_in_vid_strm_idx]->codec) != 0)
                 {
                    PRINT_MSG("Failed to Copy Context ")
                    ret = -1;
                    return ret;
                 }
                 else
                 {
                    m_out_vid_strm->sample_aspect_ratio.den = m_out_vid_strm->codec->sample_aspect_ratio.den;
                    m_out_vid_strm->sample_aspect_ratio.num = m_in_vid_strm->codec->sample_aspect_ratio.num;
                    PRINT_MSG("Copied Context ")
                    m_out_vid_strm->codec->codec_id = m_in_vid_strm->codec->codec_id;
                    m_out_vid_strm->codec->time_base.num = 1;
                    m_out_vid_strm->codec->time_base.den = m_fps*(m_in_vid_strm->codec->ticks_per_frame);         
                    m_out_vid_strm->time_base.num = 1;
                    m_out_vid_strm->time_base.den = 1000;
                    m_out_vid_strm->r_frame_rate.num = m_fps;
                    m_out_vid_strm->r_frame_rate.den = 1;
                    m_out_vid_strm->avg_frame_rate.den = 1;
                    m_out_vid_strm->avg_frame_rate.num = m_fps;
                    m_out_vid_strm->duration = (m_out_end_time - m_out_start_time)*1000;
                 }
               }
            }
      }

    if(outfmt->audio_codec != AV_CODEC_ID_NONE && m_in_aud_strm != NULL)
    {
        out_aud_codec = avcodec_find_encoder(outfmt->audio_codec);
        if(NULL == out_aud_codec)
        {
            PRINT_MSG("Could Not Find Out Aud Encoder ")
            ret = -1;
            return ret;
        }
        else
        {
            PRINT_MSG("Found Out Aud Encoder ")
            m_out_aud_strm = avformat_new_stream(m_outformat, out_aud_codec);
            if(NULL == m_out_aud_strm)
            {
                PRINT_MSG("Failed to Allocate Out Vid Strm ")
                ret = -1;
                return ret;
            }
            else
            {
                if(avcodec_copy_context(m_out_aud_strm->codec, m_informat->streams[m_in_aud_strm_idx]->codec) != 0)
                {
                    PRINT_MSG("Failed to Copy Context ")
                    ret = -1;
                    return ret;
                }
                else
                 {
                    PRINT_MSG("Copied Context ")
                    m_out_aud_strm->codec->codec_id = m_in_aud_strm->codec->codec_id;
                    m_out_aud_strm->codec->codec_tag = 0;
                    m_out_aud_strm->pts = m_in_aud_strm->pts;
                    m_out_aud_strm->duration = m_in_aud_strm->duration;
                    m_out_aud_strm->time_base.num = m_in_aud_strm->time_base.num;
                    m_out_aud_strm->time_base.den = m_in_aud_strm->time_base.den;

                }
            }
         }
      }

      if (!(outfmt->flags & AVFMT_NOFILE)) 
      {
        if (avio_open2(&m_outformat->pb, outfile.c_str(), AVIO_FLAG_WRITE,NULL, NULL) < 0) 
        {
                PRINT_VAL("Could Not Open File ", outfile)
                ret = -1;
                return ret;
        }
      }
        /* Write the stream header, if any. */
      if (avformat_write_header(m_outformat, NULL) < 0) 
      {
            PRINT_VAL("Error Occurred While Writing Header ", outfile)
            ret = -1;
            return ret;
      }
      else
      {
            PRINT_MSG("Written Output header ")
            m_init_done = true;
      }

现在您可以开始帧的编码