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• How to get time stamp of closet keyframe before a given timestamp with ffmpeg ?

  20 février 2013, par jAckOdE

  I want a ffmpeg seeking command that fast and accurate. I found this

  The solution is that we apply -ss for both input (fast seeking) and output (accurate seeking). The question is that if the input seeking is not accurate how can we be sure that the seeking position is accurate.

  For example : as the example used in the link, if we want to seek to 00:03:00, the command is something likes

  ffmpeg -ss 00:02:30 -i ... -ss 00:00:30
  As said, the first seeking will seek to somewhere else not 00:02:30, say 00:02:31. and after applying second seek, the final result would be 00:03:01- NOT what we want. Is that correct ?

  Where does fist seeking seek to ? Does it seek to k-frame that closet to 00:02:30 ?

  If so, here is my thought, correct me if i'm wrong : after first seeking, we get the timestamp of the result (in this example : 00:02:31), then we apply second seeking with appropriate time, in this case 00:00:29.

  Question is how do we get time stamp of first seeking's result ?

• avcodec_decode_video2 takes long time to decode wmv

  22 février 2013, par Mike Versteeg

  I have written a player using the ffmpeg libraries that plays several avi, mp4 and mpg files fine but not wmv. Debugging has shown that the culprit is avcodec_decode_video2 which for some reason takes half a second to decode a single wmv frame. I have tested and confirmed this with multiple wmv files, even those with much lower resolution then other files that play successfully. Anyone has a clue what I'm doing wrong ?

  PS : log shows "Extra data : 8 bits left, value : 0" and "parser not found for codec wmav2, packets or times may be invalid." for WMV files.

  UPDATE :
  Further examination has shown the call to avcodec_decode_video2 is not slow, instead it seems to return the same frame some 16 times or so, giving the visual impression that it is slow. It does not return an error code so I have no clue why it won't decode all frames in the case of wmv.

  Relevant code :

    AVPacket packet;
  
    av_init_packet(&packet);
  
    done = pOwner->av_read_frame(pFormatCtx, &packet) < 0;
  
    if (!done && packet.stream_index==videostream) 
  
        bool error = pOwner->avcodec_decode_video2(pVCodecCtx, pFrameYUV, &finished, &packet) < 0;

• avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet), the frameFinished is 0 most of the time why ?

  26 mai 2014, par Whoami

  I received a packet from rtsp by av_read_frame and decode it through

  avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet)

  After decoding i am checking the value of frameFinished.

  Most of the time i get the value of frameFinished is zero. May be around
  50% of the packet.

  Could you kindly hint me what could be the reason ?

  is this issue in any way related to ’I’, ’P’, ’B’ packet types ?