Grabframes

bool grabFrames(ffmpeg::AVFormatContext* pFormatCtx)
{
    videoStream=-1;
    for (unsigned i = 0; i < pFormatCtx->nb_streams; i++)
    {
        qDebug() << "FFmpeg stream index" << i << ":";
        ffmpeg::AVStream* avstream = pFormatCtx->streams[i];
        if (!avstream || !avstream->codec)
        {
            qDebug() << "No valid stream or codec, skipping...";
            continue;
        }
        // considering only video streams, skipping audio
        if (avstream->codec->codec_type != ffmpeg::AVMEDIA_TYPE_VIDEO)
        {
            qDebug() << "Skipping audio";
            continue;
        }

        // find the codec
        ffmpeg::AVCodec* videoCodec = avcodec_find_decoder(avstream->codec->codec_id);
        if (videoCodec == NULL)
        {
            qDebug() << "Decoder not found, skipping...";
            continue;
        }

        qDebug() << "Encoding codec" << videoCodec->name;
        // skip if the codec can't be open
        if (avcodec_open2(avstream->codec, videoCodec, NULL) < 0)
        {
            qDebug() << "Decoder failed to open, skipping...";
            continue;
        }

        pFrame = ffmpeg::avcodec_alloc_frame();
        pCodecCtx = avstream->codec;

        // Obtain from stream's number of frames if specified. Will be 0 if unknown.
        int frames = avstream->nb_frames;

        if (frames)
            qDebug() << "      Obtained from AVStream::nb_frames" << frames;

        if(videoCodec->capabilities&CODEC_CAP_TRUNCATED)
                pCodecCtx->flags|= CODEC_FLAG_TRUNCATED; // we do not send complete frames

        // We are ready to extract the frames

        while(av_read_frame(pFormatCtx, &packet) >= 0)
        {
           avcodec_get_frame_defaults(pFrame);
           int frameFinished;

           int data;
           if(packet.stream_index==i)
           {
              // Is this a packet from the video stream -> decode video frame

              data = avcodec_decode_video2(pCodecCtx,pFrame,&frameFinished,&packet);
              if(data < -1)
                  return false;
              // Did we get a video frame?
              if(frameFinished)
              {
                qDebug() << "Codec reported frame number to be " << pCodecCtx->frame_number;
              }

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