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• Capturing Clear Stills from H264 Stream

  22 octobre 2013, par David Findlay

  I'm trying to capture still images from a H264 wireless IP camera using FFMPEG. I found a similar question here : How can I extract a good quality JPEG image from an H264 video file with ffmpeg ?

  ffmpeg -y -i rtsp://10.2.69.201:554/ch0_0.h264 -r 10 -f image2 /var/www/camera.jpg

  I've implemented it as shown in that example. You can see a sample of the image I'm getting here : http://storm.woodypointcomms.com.au/camera.jpg. Basically the issue is the bottom part of the image is always blocky. If the sky has more detail and clouds the whole bottom half of the image may be blocky or blurry.

  My camera has limited stream options. One of which is I-Frame interval, you can vary it between 25-100 kbps.

  Does anyone have some suggestions about how I can get a better image ?

• 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;

• rv34 : use ff_mpeg_update_thread_context only when decoder is fully initialized

  21 août 2014, par Janne Grunau

  rv34 : use ff_mpeg_update_thread_context only when decoder is fully initialized
  MpegEncContext based decoders are only fully initialized after the first
  
  ff_thread_get_buffer() call. The RV30/40 decoders may fail before a frame
  
  buffer was requested. ff_mpeg_update_thread_context() fails on half
  
  initialized MpegEncContexts. Since this can only happen before a the
  
  first frame was decoded there is no need to call
  
  ff_mpeg_update_thread_context().
  Based on patches by John Stebbins and tested by John Stebbins.
  CC : libav-stable@libav.org
  

  • [DH] libavcodec/rv34.c