FFMPEG avcodec_decode_video2 got_picture_ptr Differing Behaviour - ffmpeg

Question

Am Currently updating our FFMPEG library usage from a pretty old version(0.5) to 2.8. As part of the change, had replaced avcodec_decode_video to avcodec_decode_video2. However, am noticing quite a difference in the way avcodec_decode_video2 functions compared to the old avcodec_decode_video. For the same packet (same data), 'avcodec_decode_video2' gives got_picture_ptr as zeo whereas the old 'avcodec_decode_video' was giving a non-zero value. In the example that am describing here, am decoding an FLV file with VideoCodec:H264-MPEG-4 AVC (part 10) and AudioCodec:MPEG AAC Audio (Am attaching a part of the Hex Version of the FLV file in FLV_Sample.Hex FLV_Sample_Hex). The original flv file is too large). For the first AVPacket (obtained from av_read_frame), got_picture_ptr from 'avcodec_decode_video2' is zero but old 'avcodec_decode_video' gives 296(Am attaching the entire AVPacket data obtained and the outputs obtained from the two functions in the file FFMPEG_Decoding_Packet_Info.txt FFMPEG_Decoding_Packet_Info). Continuing on, the new 'avcodec_decode_video2' keeps giving 'Zero' till the 23rd Packet where it gives 1. So its not like avcodec_decode_video2 keeps giving zero. My main dilemma is that am not sure if this difference in behaviour is due to the changes in 'avcodec_decode_video2' or any errors that I have made in using the Decoder. I have put a snippet of the code that am using to use the decoder below. Any suggestions will be helpful.
AVFormatContext *pFormatCtx;
AVCodecContext *pCodecCtx;
AVCodec *pCodec;
AVFrame *pFrameRGB;
#if FFMPEG_2_8
avformat_open_input(&pFormatCtx, strFileName, NULL, NULL) ;
#else
av_open_input_file(&pFormatCtx, strFileName, NULL, 0, NULL) ;
#endif //FFMPEG_2_8
size_t videoStream=pFormatCtx->nb_streams;
bool streamFound = false ;
for(size_t i=0; i<pFormatCtx->nb_streams; i++)
{
#if FFMPEG_2_8
if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO)
#else
if(pFormatCtx->streams[i]->codec->codec_type==CODEC_TYPE_VIDEO)
#endif //FFMPEG_2_8
{
videoStream = i;
streamFound = true ;
break;
}
}
if(streamFound)
{
pCodecCtx=pFormatCtx->streams[videoStream]->codec;
// Find the decoder for the video stream
pCodec=avcodec_find_decoder(pCodecCtx->codec_id);
if(pCodec==NULL)
return false; // Codec not found
// Open codec
#if FFMPEG_2_8
if(avcodec_open2(pCodecCtx, pCodec,NULL)<0)
#else
if(avcodec_open(pCodecCtx, pCodec)<0)
#endif //FFMPEG_2_8
{
return false; // Could not open codec
}
#if FFMPEG_2_8
pFrameRGB=av_frame_alloc() ;
#else
pFrameRGB=avcodec_alloc_frame();
#endif //FFMPEG_2_8
if(pFrameRGB==NULL)
return false; //No Memory
while(true)
{
AVPacket packet ;
if (av_read_frame(pFormatCtx, &packet) < 0)
{
break ;
}
int frameFinished;
if (packet.stream_index == videoStream)
{
#if FFMPEG_2_8
avcodec_decode_video2(pCodecCtx, pFrameRGB, &frameFinished, &packet);
#else
avcodec_decode_video(pCodecCtx, pFrameRGB, &frameFinished, packet.data, packet.size);
#endif //FFMPEG_2_8
}
if(frameFinished !=0)
{
break ;
}
}
}

Answer 1

I do have almost same implementation, working on latest 2.8.1 version. I have no idea about old version(0.5), but your implementation for new version seem to be fine.
I guess one thing about "got_picture_ptr ", not sure though. JFYI, decode order and display order are different in H264. May be earlier version of FFMPEG used to give out the pictures in decode order, rather than display order. In such case, you will see non-zero value for every packet decode, beginning from the first packet.
At some point, ffmpeg would have corrected this to give out the pictures in display order. Hence, you may not observe non-zero value from the very first packet decode.
I guess your application is working fine, irrespective of this difference.