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• avformat/matroskaenc : Regression fix for invalid MKV headers

  5 janvier 2017, par softworkz

  avformat/matroskaenc : Regression fix for invalid MKV headers
  The following three commits created a regression by writing initially
  
  invalid mkv headers :
  650e17d88b63b5aca6e0a43483e89e64b0f7d2dd avformat/matroskaenc : write a
  
  CRC32 element on Tags
  
  3bcadf822711720ff0f8d14db71ae47cdf97e652 avformat/matroskaenc : write a
  
  CRC32 element on Info
  
  ee888cfbe777cd2916a3548c750e433ab8f8e6a5 avformat/matroskaenc : postpone
  
  writing the Tracks master
  Symptoms :
   You can no longer playback a file that is still processed by ffmpeg,
  
  e.g. VLC fails playback
  
   You can no longer stream a file to a client while if is still being
  
  processed
  
   Various diagnosing tools show header errors or incomplete headers
  
  (e.g. ffprobe, mediainfo, mkvalidator)
  Note : The symptoms do not apply to completed files or ffmpeg runs that
  
  were interrupted with ’q’
  Cause :
  The mentioned commits made changes in a way that some header elements
  
  are only partially written in
  
  mkv_write_header, leaving the header in an invalid state. Only in
  
  mkv_write_trailer, these elements
  
  are finished correctly, but that does only occur at the end of the
  
  process.
  Regression :
  Before these commits were applied, mkv headers have always been valid,
  
  even before completion of ffmpeg.
  
  This has worked reliably over many versions of ffmpeg, to it was an
  
  obvious regression.
  Bugtracker :
  This issue has been recorded as #5977 which is resolved by this patch
  Patch :
  The patch adds a new function ’end_ebml_master_crc32_preliminary’ that
  
  preliminarily finishes the ebml
  
  element without destroying the buffer. The buffer can be used to update
  
  the ebml element later during
  
  mkv_write_trailer. But most important : mkv_write_header finishes with a
  
  valid mkv header again.
  Signed-off-by : James Almer <jamrial@gmail.com>
  

  • [DH] libavformat/matroskaenc.c

• FFmpeg How to use alimiter Filter ?

  21 décembre 2016, par Matt McManis

  I cannot find enough documentation on the alimiter filter.

  https://ffmpeg.org/ffmpeg-filters.html#alimiter

  I used -filter_complex alimiter=limit=0.5 and it applied to the file but it boosted the volume.

  I thought it was supposed to hardlimit the volume down ?

  FFmpeg says through cmd limit range [0.0625 - 1]

  ffmpeg -i audio.wav -y -acodec libmp3lame -b:a 320k -ar 44100 -ac 2 -joint_stereo 1 -filter_complex alimiter=limit=0.5 audio.mp3

  Here’s a look at the two files through Adobe Audition

  Original

  

  FFmpeg alimiter 0.5

  

• Using -itsoffset with AAC Tracks in MP4 : What Actually Happens ? [closed]

  10 avril, par user27607034

  If the frame duration of an AAC file is around 21 milliseconds, does the itsoffset value in the following command actually get applied ? And even if it does, will players like QuickTime or a smart TV actually respect it ?

  


  ffmpeg -itsoffset 0.009 -i input.mp4 \
  -i input.mp4 \
  -map 1:v:0 \ // hevc
  -map 0:a:0 \ // aac
  -c copy \
  output.mp4