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• To get OpenCV VideoWriter work across platforms consistently for MP4 container with H264 encoding

  28 mars 2019, par Moh

  I am trying to get OpenCV VideoWriter work across platform consistently for MP4 container with H246 encoding.

  Target platforms in order of importance - Ubuntu, Raspbian, OSX

  Basically, my shortcoming at this point is not understanding the relationship of FourCC code (as a parameter to OpenCV VideoWriter) to the FFMPEG backend and its requirements. I am interested to understand the game in play rather than discussing a piece of code.

  What I want to know is when I specify ’X264’ as FourCC code trying to write an x.MP4 file (FFMPEG backend) and the request is marshalled to FFMPEG what requirements/dependencies need to be satisfied by the OS for it to success.

  So far I have got my python stack writing MP4 video files across Raspbian/Ubuntu/OSX, with a hack.

  On my Raspbian stretch installation, I use 0x00000021 as the fourCC code.
  On Ubuntu (VM on OSX) and on OSX, AVC1 works.

  Days of Googling only delivered those hacks, not a good understanding of the problem.

  The x264 as FourCC code leads to one of - failure, non-portable video file + annoying FFMPEG warning.

  I am trying to get to the bottom of it.

  The code,

      #self.__fourCC = cv2.VideoWriter_fourcc('x', '2', '6', '4')
  
      self.__fourCC = cv2.VideoWriter_fourcc('a', 'v', 'c', '1')
  
      if PlatformUtils.isRunningOnRaspberryPi():
  
          self.__fourCC = 0x00000021

  I have control over the version both OpenCV and FFMPEG (if required GStreamer too). I can and have built them for Ubuntu/Raspbian.

• h264_mp4toannexb : Consistently use pointer comparisons

  14 décembre 2019, par Andreas Rheinhardt

  h264_mp4toannexb : Consistently use pointer comparisons
  h264_mp4toannexb_filter currently uses both indices/offsets as well as
  
  direct pointers comparisons for the checks whether one has reached or
  
  even surpassed the end. This commit removes the offsets.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavcodec/h264_mp4toannexb_bsf.c

• avcodec/bitstream : Consistently treat symbol as VLC_TYPE

  26 octobre 2020, par Andreas Rheinhardt

  avcodec/bitstream : Consistently treat symbol as VLC_TYPE
  If a static VLC table gets initialized a second time (or concurrently by
  
  two threads) and if said VLC table uses symbols that have the sign bit
  
  of VLC_TYPE (a typedef for int16_t) set, initializing the VLC fails. The
  
  reason is that the type of the symbol in the temporary array is an
  
  uint16_t and so comparing it to the symbol read from the VLC table will
  
  fail, because only the lower 16bits coincide. Said failure triggers an
  
  assert.
  Reviewed-by : Lynne <dev@lynne.ee>
  
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavcodec/bitstream.c