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• Why additional encoders are displayed in ffmpeg command line output "encoder : Lavf58.20.100" ?

  4 décembre 2019, par Raghvendra Kumar

  When converting multimedia files using ffmpeg command line tool it displays additional encoders in the console in metadata section.

  I am trying to convert a .mp4 file with
  video stream encoded as

  h264 -> av1

  and audio stream encoded as

  aac -> aac

  It displays the following on the console :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'input.mp4':   Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      encoder         : Lavf57.71.100

  What is encoder : Lavf57.71.100 here ?

  I am trying to make sense of this info but this is not an encoder as per my knowledge or I am missing something ?

• Standardized "Skip Intro" in MP4 video files ?

  25 mai 2020, par Crissov

  Is there a standardized way to mark up specific parts of a MP4-contained video as skippable, e.g. trailers, recaps, intros/outros, opening/closing credits, in the metadata in the file itself ? If possible, I would like to set this with FFmpeg or MP4box.

  



  I know that the mvhd box in MOV files makes it possible to specify a single preview. 
I assume Netflix and the like use specially named or hinted chapters, either from file-internal metadata or from a central database, to provide this feature. 
I want to add this now to videos in my personal library, just in case Kodi, VLC or other players and media centers add support for this feature.

  



  Edit List Box elst

  



  As mentioned in the first comment, Edit Lists may be a solution. They are specified in section 8.6.6 of ISO/IEC 14496-12:2015 (ISOBMFF), which I partially cite below.

  



  moov > trak+ > edts ? > elst*

  



  


  [elst] contains an explicit time-line map. 
 Each entry defines part of the track time-line :
  
 by mapping part of the media time-line,
  
 or by indicating ‘empty’ time,
  
 or by defining a ‘dwell’, where a single time-point in the media is held for a period.

  
 


  

  • version is an integer that specifies the version of this box (0 or 1)

  


  • entry_count is an integer that gives the number of entries in the following table

  


  • segment_duration is an integer that specifies the duration of this edit segment in units of the timescale in the Movie Header Box

  


  • media_time is an integer containing the starting time within the media of this edit segment (in media time scale units, in composition time). If this field is set to –1, it is an empty edit. The last edit in a track shall never be an empty edit. Any difference between the duration in the Movie Header Box, and the track’s duration is expressed as an implicit empty edit at the end.

  


  • media_rate specifies the relative rate at which to play the media corresponding to this edit segment. If this value is 0, then the edit is specifying a ‘dwell’ : the media at media-time is presented for the segment-duration. Otherwise this field shall contain the value 1.

  


  


  


• Ffmpeg mathematical "expression" syntax in filters

  9 novembre 2022, par Jason C

  Multiple ffmpeg filters take a mathematical expression as a parameter, for example setpts and select (examples from docs) :

  


  setpts='1/(25*TB) * (N + 0.05 * sin(N*2*PI/25))';
select=select=between(t\,10\,20)


  


  The docs for each filter are generally good about listing available variables for that specific filter, but the actual syntax of this expression appears (?) to be completely undocumented, despite its heavy use. For example, what functions are available (e.g. sin, between) ? Are boolean combinations allowable and if so, what are the operators ? What other mathematical operators are available ?

  


  What is the syntax of these expressions ? Or, at the very least, is some non-ffmpeg library parsing them and if so, what is it ? That way I can at least look up the syntax. Or have I missed some documentation section somewhere...?