[Libav-user] mpeg4 decoding only decodes 36395 out of 154959 frames

[Alex Cohn]

On May 11, 2012 12:12 PM, "Bob Self" <bobslf at gmail.com> wrote:
>
> I finally found an incomplete example that I was able to get sort-of
working
> with non-deprecated functions. The only error (or warning?) that I get is
> "[mpeg4 @ 0x1367c80] Invalid and inefficient vfw-avi packed B frames
detected"
> once. Other than that the program runs without errors, but there is still
> something that I don't understand.
>
> pFormatCtx->streams[videoStream]->nb_frames says that there are 154,959
frames
> But if I count the decoded frames (frame++), I only get 36,395 frames
> before the loop quits. Why does this happen?
>
nb_frames may be not reliable. How many frames does ffmpeg command decide?

BR,
Alex Cohn

> the program output:
> -------------------------------
>
> [avi @ 0x1361920] Format avi probed with size=2048 and score=100
> [AVI demuxer @ 0x1361e60] use odml:1
> st:1 removing common factor 128 from timebase
> [mpeg4 @ 0x1367c80] Invalid and inefficient vfw-avi packed B frames
detected
> [avi @ 0x1361920] All info found
> Input #0, avi, from 'test.avi':
>  Metadata:
>    encoder         : FairUse Wizard - http://fairusewizard.com
>  Duration: 01:47:43.08, start: 0.000000, bitrate: 1815 kb/s
>    Stream #0:0, 1, 1001/24000: Video: mpeg4 (Advanced Simple Profile)
> (XVID / 0x44495658), yuv420p, 688x368 [SAR 1:1 DAR 43:23], 1001/24000,
> 23.98 tbr, 23.98 tbn, 23.98 tbc
>    Stream #0:1, 21, 3/125: Audio: mp3 (U[0][0][0] / 0x0055), 48000
> Hz, stereo, s16, 128 kb/s
>
>
> the test function:
> ----------------------------
>
> int test(void)  {
>   const char *inputfile = "test.avi";
>   int totalFrames = 0;
>   int frameLocation = 0;
>   AVFormatContext *pFormatCtx;
>   unsigned int    i, videoStream;
>   AVCodecContext  *pCodecCtx;
>   AVCodec         *pCodec;
>   AVFrame         *pFrame;
>   AVFrame         *pFrameYUV;
>   int             numBytes;
>   uint8_t         *buffer;
>   int status;
>   unsigned int codec_version;
>
>   av_register_all();
>
>   codec_version = avcodec_version();
>   // avcodec version: 54.10.100
>   printf("avcodec version = %d.%d.%d\n",
> (codec_version&0x00ff0000)>>16, (codec_version&0x0000ff00)>>8,
> codec_version&0x000000ff);      // version 52.72.2
>
>   av_log_set_level(AV_LOG_DEBUG);
>
>   pFormatCtx = avformat_alloc_context();
>
>   status = avformat_open_input(&pFormatCtx, inputfile, NULL, NULL);
>   if (status != 0)  {
>      return -1;
>   }
>
>   status = avformat_find_stream_info(pFormatCtx, NULL);
>   if (status<0)  {
>      return -2;
>   }
>
>   av_dump_format(pFormatCtx, 0, inputfile, false);
>
>   videoStream=-1;
>
>   for(i=0; i<pFormatCtx->nb_streams; i++) {
>      if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO) {
>         videoStream=i;
>         break;
>      }
>   }
>   if(videoStream==-1) {
>      return -3;
>   }
>
>   pCodecCtx = pFormatCtx->streams[videoStream]->codec;
>
>   double duration = double(pFormatCtx->duration) / AV_TIME_BASE;
>
>   pCodec=avcodec_find_decoder(pCodecCtx->codec_id);
>   if(pCodec==NULL) {
>      return -4;
>   }
>
>   if(pCodec->capabilities & CODEC_CAP_TRUNCATED)  {
>      pCodecCtx->flags|=CODEC_FLAG_TRUNCATED;
>   }
>
>   if(avcodec_open2(pCodecCtx, pCodec, NULL)<0)  {
>      return -5;
>   }
>
>   printf("Using codec: %s\n", pCodec->name);
>
>   pFrame = avcodec_alloc_frame();
>
>   pFrameYUV=avcodec_alloc_frame();
>   if(pFrameYUV==NULL)  {
>      return -6;
>   }
>
>   numBytes = avpicture_get_size(PIX_FMT_YUV420P, pCodecCtx->width,
> pCodecCtx->height);       // 379776
>   buffer = (uint8_t *)av_malloc(numBytes*sizeof(uint8_t));
>
>   avpicture_fill((AVPicture *)pFrameYUV, buffer, PIX_FMT_YUV420P,
> pCodecCtx->width, pCodecCtx->height);
>
>   totalFrames = pFormatCtx->streams[videoStream]->nb_frames;
>   // 154959
>   printf("Frames: %d\n", totalFrames);
>
>   AVPacket packet;
>   int isFrameFinished = 0;
>   int pixelScanCount = 0;
>
>   printf("video width = %d\n", pCodecCtx->width);
>   printf("video height = %d\n", pCodecCtx->height);
>
>   int frame = 0;
>   int loops = 0;
>
>   while (av_read_frame(pFormatCtx, &packet) >= 0)  {
>      status = av_read_frame(pFormatCtx, &packet);
>      if (status<0)  {
>         break;
>      }
>
>      loops++;
>
>      if (packet.stream_index == videoStream)  {
>         status = avcodec_decode_video2(pCodecCtx, pFrame,
> &isFrameFinished, &packet);
>         if (isFrameFinished) {
>            frame++;
>
>            if ( (frame%1000) == 0)  {
>               printf("%d\n", frame);
>            }
>
>            pixelScanCount = 0;
>
>            for (int y = 0; y < pCodecCtx->height; y++)  {
>               uint8_t *p = pFrame->data[0] + y * pFrame->linesize[0];
>
>               for (int x = 0; x < pCodecCtx->width; x++)  {
>                  pixelScanCount++;
>               }
>            }
>            av_free_packet(&packet);
>
>         }
>         else  {
>            av_free_packet(&packet);
>         }
>      }
>   }
>
>
>   printf("frame = %d\n", frame);               // frame = 36395
>   printf("loops = %d\n", loops);               // loops = 212127
>   printf("totalFrames = %d\n", totalFrames);   // totalFrames = 154959
>
>   delete [] buffer;
>   av_free(pFrameYUV);
>   av_free(pFrame);
>   avcodec_close(pCodecCtx);
>   avformat_close_input(&pFormatCtx);
>
>   return 0;
> }
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