Recherche avancée

Sur d’autres sites (4836)

• avformat/matroskaenc : Actually apply timestamp offset for Opus

  31 août 2022, par Andreas Rheinhardt

  avformat/matroskaenc : Actually apply timestamp offset for Opus
  Matroska generally requires timestamps to be nonnegative, but
  
  there is an exception : Data that corresponds to encoder delay
  
  and is not supposed to be output anyway can have a negative
  
  timestamp. This is achieved by using the CodecDelay header
  
  field : The demuxer has to subtract this value from the raw
  
  (nonnegative) timestamps of the corresponding track.
  
  Therefore the muxer has to add this value first to write
  
  this raw timestamp.
  Support for writing CodecDelay has been added in FFmpeg commit
  
  d92b1b1babe69268971863649c225e1747358a74 and in Libav commit
  
  a1aa37dd0b96710d4a17718198a3f56aea2040c1. The former simply
  
  wrote the header field and did not apply any timestamp offsets,
  
  leading to desynchronisation (if one uses multiple tracks).
  
  The latter applied it at two places, but not at the one where
  
  it actually matters, namely in mkv_write_block(), leading to
  
  the same desynchronisation as with the former commit. It furthermore
  
  used the wrong stream timebase to convert the delay to the
  
  stream's timebase, as the conversion used the timebase from
  
  before avpriv_set_pts_info().
  When the latter was merged in 82e4f39883932c1b1e5c7792a1be12dec6ab603d,
  
  it was only done in a deactivated state that still did not
  
  offset the timestamps when muxing due to "assertion failures
  
  and av sync errors". a1aa37dd0b96710d4a17718198a3f56aea2040c1
  
  made it definitely more likely to run into assertion failures
  
  (namely if the relative block timestamp doesn't fit into an int16_t).
  Yet all of the above issues have been fixed (in commits
  
  962d63157322466a9a82f9f9d84c1b6f1b582f65,
  
  5d3953a5dcfd5f71391b7f34908517eb6f7e5146 and
  
  4ebeab15b037a21f195696cef1f7522daf42f3ee. This commit therefore
  
  enables applying CodecDelay, fixing ticket #7182.
  There is just one slight regression from this : If one has input
  
  with encoder delay where the first timestamp is negative, but
  
  the pts of the part of the data that is actually intended to be
  
  output is nonnegative, then the timestamps will currently by default
  
  be shifted to make them nonnegative before they reach the muxer ;
  
  the muxer will then ensure that the shifted timestamps are retained.
  
  Before this commit, the muxer did not ensure this ; instead the
  
  timestamps that the demuxer will output were shifted and
  
  if the first timestamp of the actually intended output was zero
  
  before shifting, then this unintentional shift just cancels
  
  the shift performed before the packet reached the muxer.
  
  (But notice that this only applies if all the tracks use the same
  
  CodecDelay, or the relative sync between tracks will be impaired.)
  
  This happens in the matroska-opus-remux and matroska-ogg-opus-remux
  
  FATE tests. Future commits will forward the information that
  
  the Matroska muxer has a limited capability to handle negative
  
  timestamps so that the shifting in libavformat can take advantage
  
  of it.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavformat/matroskaenc.c
  • [DH] tests/ref/fate/matroska-ogg-opus-remux
  • [DH] tests/ref/fate/matroska-opus-remux

• ffmpeg output file smaller than input file

  3 mai 2020, par Debug255

  I am using ffmpeg to rotate videos 90 or 180 degrees in a Python script. It works great. But, I am curious as to why the output file would be a smaller amount of bytes than the input file.

  



  Here are the commands I use :

  



  180 degrees :

  



  ffmpeg -i ./input.mp4 -preset veryslow -vf "transpose=2,transpose=2,format=yuv420p" -metadata:s:v rotate=0 -codec:v libx264 -codec:a copy ./output.mp4

  



  90 degrees :

  



  ffmpeg -i ./input.mp4 -vf "transpose=2" ./output.mp4

  



  For example, a GoPro Hero 3 MP4 file was originally 2.0 GB. The resulting output file was 480.9 MB. Another GoPro file was 2.0 and its resulting file was 671.5 MB. Is this maybe because the GoPro files were 2.0 but contains empty space, sort of like how some NTFS filesystems make a minimal 4k file, even when there is less bytes in it ?

  



  If this isn't the GoPro Hero 3, how do I rotate the files 90 or 180 degrees but ensure the output file size is the same ? Or, is data loss expected ? Does the data loss have to do with the format ?

  



  Note that the quality of the video doesn't appear to be damaged, which is good. So, I am interested in learning more about why this is happening, then I can read the section of ffmpeg documentation that is relevant to this.

  



  Thank you !

  


• ffms : Various improvements

  31 janvier 2016, par Henrik Gramner

  ffms : Various improvements
   * Drop the MinGW Unicode workarounds. Those were required at the time
  
     Windows Unicode support was added to x264 but the underlying problem
  
     has since been fixed in FFMS.
   * Use FFMS_IndexBelongsToFile() as an additional sanity check when reading
  
     an index file to ensure that it belongs to the current source video.
   * Upgrade to the new API to prevent deprecation warnings when compiling.
   * Fix a resource leak that would occur if FFMS_GetFirstTrackOfType() or
  
     FFMS_CreateVideoSource() failed.
   * Minor string handling adjustments related to progress reporting.
  This increases the FFMS version requirement from 2.16.2 to 2.21.0.
  

  • [DH] configure
  • [DH] input/ffms.c