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• dnxhddec : Decode and use interlace mb flag

  26 septembre 2015, par Christophe Gisquet

  dnxhddec : Decode and use interlace mb flag
  This bit is 1 in some samples, and seems to coincide with interlaced
  
  mbs and CID1260. 2008 specs do not know about it, and maintain qscale
  
  is 11 bits. This looks oversized, but may help larger bitdepths.
  Currently, it leads to an obviously incorrect qscale value, meaning
  
  its syntax is shifted by 1. However, reading 11 bits also leads to
  
  obviously incorrect decoding : qscale seems to be 10 bits.
  However, as most profiles still have 11bits qscale, the feature is
  
  restricted to the CID1260 profile (this flag is dependent on
  
  a higher-level flag located in the header).
  The encoder writes 12 bits of syntax, last and first bits always 0,
  
  which is now somewhat inconsistent with the decoder, but ends up with
  
  the same effect (progressive + reserved bit).
  Signed-off-by : Vittorio Giovara <vittorio.giovara@gmail.com>
  

  • [DBH] libavcodec/dnxhddec.c

• JavaCV FFmpegFrameRecorder properties explanation needed

  29 décembre 2014, par Leron

  I’m using FFmpegFrameRecorder to get the video input from my webcam and record it into a video file. The problem is that I’m building my application using a few different demo source codes that I found and I use properties some of which are not completely clear to me.

  First, here is my code snippet :

  FFmpegFrameRecorder recorder = new FFmpegFrameRecorder(FILENAME,  grabber.getImageWidth(),grabber.getImageHeight());
  
  
  
          recorder.setVideoCodec(13);
  
          recorder.setFormat("mp4");
  
          recorder.setPixelFormat(avutil.PIX_FMT_YUV420P);
  
          recorder.setFrameRate(30);
  
          recorder.setVideoBitrate(10 * 1024 * 1024);
  
  
  
          recorder.start();

  • setVideoCodec(13) - What is the meaning of this (13) how can I understand what actual codec stands behind any number ?
  • setPixelFormat - Just get this, don’t know what it’s doing in general
  • setFrameRate(30) - I think this should be pretty clear but still what is the logic behind what frame rate we choose (isn’t the high the better ?)
  • setVideoBitrate(10*1024*1024) - again almost no idea what this does and what’s the logic behind the numbers ?

  At the end I just want to mention one last problem that I get recording video like this. If the actual length of the video is let’s say 20secs. When I play the video file created from the program it runs significantly faster. Can’t tell if it’s exactly 2 times faster than it should be but in general if I record a 20sec video then it’s played for about 10secs. What may cause this and how can I fix it ?

• avcodec/v4l2_m2m_dec : remove redundant packet and fix double free

  16 juillet 2020, par Andriy Gelman

  avcodec/v4l2_m2m_dec : remove redundant packet and fix double free
  v4l2_receive_frame() uses two packets s->buf_pkt and avpkt. If avpkt
  
  cannot be enqueued, the packet is buffered in s->buf_pkt and enqueued in
  
  the next call. Currently the ownership transfer between the two packets
  
  is not properly handled. A double free occurs if
  
  ff_v4l2_context_enqueue_packet() returns EAGAIN and v4l2_try_start
  
  returns EINVAL.
  In fact, having two AVPackets is not needed and everything can be
  
  handled by s->buf_pkt.
  This commit removes the local avpkt from v4l2_receive_frame(), meaning
  
  that the ownership transfer doesn't need to be handled and the double
  
  free is fixed.
  Signed-off-by : Andriy Gelman <andriy.gelman@gmail.com>
  

  • [DH] libavcodec/v4l2_m2m_dec.c