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• Use QT format for audio sample descriptors depending on stsd version.

  5 septembre 2018, par Justin Ruggles

  Use QT format for audio sample descriptors depending on stsd version.
  ISOBMFF does not allow AudioSampleEntryV1 in stsd version 0, so
  
  assume the descriptor format is QTFF SoundDescriptionV1. ISOBMFF does
  
  not define a version 2.
  This fixes audio decoding for some MP4 files generated with Apple
  
  tools. The additional fields present in SoundDescriptionV1/V2 need to
  
  be read in order to correctly read additional boxes that contain
  
  information required for decoding the stream.
  Fixes #7376.
  Also see : https://github.com/HandBrake/HandBrake/issues/1555
  Signed-off-by : Derek Buitenhuis <derek.buitenhuis@gmail.com>
  

  • [DH] libavformat/isom.h
  • [DH] libavformat/mov.c

• Seek in fragmented MP4

  15 novembre 2020, par Stefan Falk

  For my web-client I want the user to be able to play a track right away, without having to download the entire file. For this I am using a fragmented MP4 with the AAC audio coded (Mime-Type : audio/mp4; codecs="mp4a.40.2").

  


  This is the command that is being used in order to convert an input file to a fMP4 :

  


  ffmpeg -i /tmp/input.any \
  -f mp4 \
  -movflags faststart+separate_moof+empty_moov+default_base_moof \
  -acodec aac -b:a 256000 \
  -frag_duration 500K \
   /tmp/output.mp4


  


  If I look at this file on MP4Box.js, I see that the file is fragmented like this :

  


  ftyp
moov
moof
mdat
moof
mdat
..
moof
mdat
mfra


  


  This looks alright so far but the problem I am facing now is that it's not apparent to me how to start loading data from a specific timestamp without introducing an additional overhead. What I mean by this is that I need the exact byte offset of the first [moof][mdat] for a specific timestamp without the entire file being available.

  


  Let's say I have a file that looks like this :

  


  ftyp
moov
moof # 00:00
mdat 
moof # 00:01
mdat
moof # 00:02
mdat
moof # 00:03
mdat
mfra


  


  This file however, is not available on my server directly, it is being loaded from another service, but the client wants to request packets starting at 00:02.

  


  Is there a way to do this efficiently without me having to load the entire file from the other service to my server ?

  


  My guess would be to load [ftyp][moov] (or store at least this part on my own server) but as far as I know, the metadata stored in those boxes won't help me to find a byte-offset to the first [moof][mdat]-pair.

  


  Is this even possible or am I following the wrong approach here ?

  


• movenc : Allow writing timed ID3 metadata

  17 janvier 2024, par Martin Storsjö

  movenc : Allow writing timed ID3 metadata
  This is based on a spec at https://aomediacodec.github.io/id3-emsg/,
  
  further based on ISO/IEC 23009-1:2019.
  Within libavformat, timed ID3 metadata (already supported by the
  
  mpegts demuxer and muxer) is handled as a separate data AVStream
  
  with codec type AV_CODEC_ID_TIMED_ID3. However, it doesn't
  
  have a corresponding track in the mov file - instead, these events
  
  are written as separate toplevel 'emsg' boxes.
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DH] libavformat/movenc.c
  • [DH] libavformat/tests/movenc.c
  • [DH] tests/ref/fate/movenc