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• Converting avi to mp4 : audio is out of sync

  17 octobre 2011, par M.S

  I'm using ffmpeg to convert a video from avi to mp4.
  The audio / video in the output mp4 are out of sync. I researched and found the following link, which suggests that this is an issue with newer builds of ffmpeg :

  http://forum.videohelp.com/threads/320342-Audio-out-of-sync-problem-with-FFMPEG-encoding-MP4-%28h-264-AAC%29?p=1983858&viewfull=1#post1983858

  I tried build 18715 as suggested and indeed the a/v is in sync. I thought I'd just use this build, but I then realized that the output file size is much larger (about a third more). Any idea why ? Bandwidth is currently a major concern in my application.

  I'm trying to either solve the sync problem with the latest build or figure out how to reduce the size of the file with the older build. Any suggestions ?

  EDIT :
  The command I use for the conversion :

  ffmpeg -i test.avi -vb 100k -ab 48k -r 20 test.mp4

  This is a very low res and quite static video and the low bitrate is adequate (and isn't a cause for any problem when not using mp4).

• What codec in OpenCV can do a stronger compression than default 'mp4v' ? [closed]

  7 juillet, par ullix

  My project does video recording from a microscope camera, and one experiment can run for days and even weeks. This takes plenty of filespace, so I want as strong a compression as possible. Quality is not a major concern.

  


  Currently I use the default 'mp4v' codec with opencv on Python. It works.

  


  I tried all codecs Google could find, and surprisingly, only very few worked. And those few that did work were even worse in compression.

  


  Where is the limitation ? Is it Opencv (4.11.0.86) ? Is it FFMPEG (7.1.1) ? Is it the distribution (Ubuntu Mate 25.04) ? Is it the CPU (AMD Ryzen AI 9 HX 370 w/ Radeon 890M × 24) ?

  


  EDIT :
I have uploaded an example clip (1 min) with some explanations to youtube :
https://www.youtube.com/watch?v=wW8w2Pppnng
Frames are FullHD, constant 10FPS

  


  The stripped-down code is :

  


  import cv2
fourcc = cv2.VideoWriter_fourcc(*'mp4v')
out    = cv2.VideoWriter("myvideo.mp4", fourcc, 19,(1920, 1080))
cam    = cv2.VideoCapture(0)
# loop
  success, image = cam.read()              
  cv2.imshow(title, image)                 
  key = cv2.waitKey(1)                     
  out.write(image)
...
out.release()


  


  What alternative codec can I use which gives better compression ?

  


• avformat/wtvdec : Forward errors when reading packet

  10 février 2020, par Andreas Rheinhardt

  avformat/wtvdec : Forward errors when reading packet
  wtvfile_read_packet did not abide by the requirements of an
  
  AVIOContext's read_packet-function : If it did not read anything,
  
  it returned zero, which currently leads to a warning in read_packet_wrapper
  
  in aviobuf.c. Said warning will be an av_assert2 as soon as
  
  FF_API_OLD_AVIO_EOF_0 is zero (probably the next major version bump).
  
  So instead forward the error code from the underlying protocol.
  This error/assert is triggered in the wtv-demux FATE test.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  
  Reviewed-by : Peter Ross <pross@xvid.org>
  
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavformat/wtvdec.c