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• issue in converting a stream of images that is jittery and lossy into a video (using ffmpeg or otherwise)

  17 mars 2019, par ksridhar

  i have a program that is the source for png images that are sent out on its stdout. this program is prone to lose images as well have jitter (not deliver them on time precisely i.e. 25 frames/sec).

  i tried the following with ffmpeg

  image_streamer.sh | ffmpeg -vcodec png -i - -vf fps=25 -vcodec libx264 -y foo.mp4.

  it was noticed that (a) when the input rate was wavering around 25 frames/sec with no drops the mp4 file was created fine but when (b) there were drops by the image_streamer.sh the fps filter did not duplicate images. i understand that there is no pts information in this case.

  i read several questions/answers around this issue but there we related to files and not a pipe.

  There was also a thread of conversation a long time back (https://ffmpeg.org/pipermail/ffmpeg-user/2012-December/011855.html) but it lead to a dead end.

  i am quite naive to ffmpeg. i hope that this question is not something really stupid.

• rtmpproto : Validate the embedded flv packet size before copying

  3 octobre 2013, par Martin Storsjö

  rtmpproto : Validate the embedded flv packet size before copying
  This wasn’t an issue prior to 58404738, when the whole RTMP packet
  
  was copied at once and the length of the individual embedded flv
  
  packets only were validated by the flv demuxer.
  Prior to this patch, this could lead to reads and writes out of bound.
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DBH] libavformat/rtmpproto.c

• avcodec/mpegvideo_enc : Fix a chroma mb size error in sse_mb()

  4 juillet 2022, par Wenbin Chen

  avcodec/mpegvideo_enc : Fix a chroma mb size error in sse_mb()
  For 422 frames we should not use hard coded 8 to calculate mb size for
  
  uv plane. Chroma shift should be taken into consideration to be
  
  compatiple with different sampling format.
  The error is reported by fate test when av_cpu_max_align() return 64
  
  on the platform supporting AVX512. This is a hidden error and it is
  
  exposed after commit 17a59a634c39b00a680c6ebbaea58db95594d13d.
  mpeg2enc has a mechanism to reuse frames. When it computes SSE (sum of
  
  squared error) on current mb, reconstructed mb will be wrote to the
  
  previous mb space, so that the memory can be saved. However if the align
  
  is 64, the frame is shared in somewhere else, so the frame cannot be
  
  reused and a new frame to store reconstrued data is created. Because the
  
  height of mb is wrong when compute sse on 422 frame, starting from the
  
  second line of macro block, changed data is read when frame is reused
  
  (we need to read row 16 rather than row 8 if frame is 422), and unchanged
  
  data is read when frame is not reused (a new frame is created so the
  
  original frame will not be changed).
  That is why commit 17a59a634c39b00a680c6ebbaea58db95594d13d exposes this
  
  issue, because it add av_cpu_max_align() and this function return 64 on
  
  platform supporting AVX512 which lead to creating a frame in mpeg2enc,
  
  and this lead to the different outputs.
  Signed-off-by : Wenbin Chen <wenbin.chen@intel.com>
  
  Signed-off-by : Marton Balint <cus@passwd.hu>
  

  • [DH] libavcodec/mpegvideo_enc.c
  • [DH] tests/ref/seek/vsynth_lena-mpeg2-422
  • [DH] tests/ref/vsynth/vsynth1-mpeg2-422
  • [DH] tests/ref/vsynth/vsynth2-mpeg2-422
  • [DH] tests/ref/vsynth/vsynth3-mpeg2-422
  • [DH] tests/ref/vsynth/vsynth_lena-mpeg2-422