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• Converting mkv to h264 FFmpeg

  14 janvier 2021, par Rikus Honey

  EDIT :
This question has become very popular and is one of the top results for searching "convert mkv to h264 ffmpeg" and thus I feel it is appropriate to add that for anyone stumbling upon this question to rather use

  


  ffmpeg -i input.mkv -c:v libx264 -c:a aac output.mp4


  


  as libvo_aacenc has been removed in recent versions of FFmpeg and it now has a native aac encoder. For more information visit the FFmpeg wiki page for encoding AAC.

  


  Here is the original question :

  


  I would like to convert my .mkv files to .mp4 using FFmpeg. I have tried the following code :

  


  ffmpeg -i input.mkv -c:v libx264 -c:a libvo_aacenc output.mp4


  


  But I get the error :

  


  


  Error while opening encoder for output stream #0:1 - maybe incorrect parameters such as bit_rate, rate, width or height.

  


  


  Is there any way to get around this ? I have tried setting the bitrate of the audio but the problem seems to persist.

  


• x86 : Avoid self-relative expressions on macho64

  23 mai 2017, par Henrik Gramner

  x86 : Avoid self-relative expressions on macho64
  Functions that uses self-relative expressions in the form of [foo-$$]
  
  appears to cause issues on 64-bit Mach-O systems when assembled with nasm.
  
  Temporarily disable those functions on macho64 for the time being until
  
  we've figured out the root cause.
  

  • [DH] common/bitstream.c
  • [DH] common/pixel.c
  • [DH] common/quant.c
  • [DH] encoder/cabac.c
  • [DH] encoder/rdo.c

• Precise cut of remote video file

  20 août 2014, par Nicolas Goy

  I have hours long video files living on a server, and I need to be able to cut segments in them in an accurate and fast way.

  I tried :

  ffmpeg -ss 10:00 -i http://server/input.mp4 -t 5:00 -vcodec copy -acodec copy out.mp4

  This works and is fast, but it’s not precise as ffmpeg seeks backward until it finds a keyframe. The resulting video file ends up with a negative start time which is not working nice with browsers.

  I know I can re-encode the video for accurate seeking, but this would be slow and lose quality.

  I came up with the following idea :

  For example, let’s say we have a 20 seconds video, with keyframes every 5 secs, at 0,5,10,15,20.

  If I want a segment from sec 2 to sec 17, I would re-encode from sec 2 to 5, vcopy from sec 5 to 15, re-encode from sec 15 to 17 and concat the three files.

  This is the general problem and my idea, now the requirements are :

  • Source files must be accessed over HTTP
  • There must be no or very few quality loss
  • It must be fast, cutting 10 minutes in a 2h video should take around 1-2 sec
  • It must be accurate
  • It must work for webm and mp4

  It doesn’t have to be a ffmpeg command, I’m quite sure I’ll have to write a C wrapper around libav.

  Source file can be pre-processed in any necessary way to make it work.

  UPDATE : After getting more info, it seems my "idea" of gluing re-encoded extremities parts with a stream copied middle part won’t work because of different encoding settings. But I could extract a longuer part (keyframe -> keyframe) and extract timecodes I could add in an HTTP header, like Time-Range: 0.25,15.14 which would mean "play from sec 0.25 to 15.14 and discard the rest".