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• Merge two videos with different HTTP Range header bytes

  5 avril 2022, par Mohammad Momeni

  I want to save 10 seconds from any part of a video by using its URL (without downloading it completely).
the server supports the Range header and it's possible to get specific byte ranges, the video is ok when I save it with something like Range: bytes=0-102400 but when I change the start byte and save a video with Range: bytes=307200-614400 it's no longer playable.

  


  I know maybe it lacks a MIME/header type that should be at the beginning of a file, but the first bytes are not in this response to specify the correct format of the file.
so I saved the video from 0-102400, which is ok and playable, and wanted to get that specific range and somehow append it after the first file to have both a correct file header (less than 1 sec) and that middle part of the video.

  


  first.webm Range : bytes=0-102400 (valid playable file)

  


  middle.webm Range : bytes=307200-614400 (not playable file)

  


  I tried to merge them using this command recommended by this answer

  


  ffmpeg -f concat -i list.txt -c copy merged.webm


  


  logs :

  


  [matroska,webm @ 000002143c3e77c0] File ended prematurely00 bitrate=3752.0kbits/s speed=N/A
[matroska,webm @ 000002143c429e40] Format matroska,webm detected only with low score of 1, misdetection possible!
[matroska,webm @ 000002143c429e40] EBML header parsing failed
[concat @ 000002143c3dda80] Impossible to open 'middle.webm'
list.txt: Invalid data found when processing input
frame=   42 fps=0.0 q=-1.0 Lsize=      10kB time=00:00:01.64 bitrate=  48.7kbits/s speed= 231x    
video:9kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 8.500000%


  


  generated video only shows the first video (which was already playable before merging) and ends.
I inspired this idea from this answer and don't want to download the complete video. If I can't merge them is it possible and how to write a MIME/header for the middle.webm manually to make it a valid playable video ?

  


• avformat/matroskadec : Fix probing of unknown-length headers

  17 mai 2019, par Andreas Rheinhardt

  avformat/matroskadec : Fix probing of unknown-length headers
  matroska_probe did not support the case of an unknown-length EBML header
  
  at all ; given that libavformat's Matroska muxer used to produce such
  
  files in the streaming case, support for them has been added.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavformat/matroskadec.c

• ffmpeg flac or mp3 to m4a - exactly the same length possible ?

  17 février 2021, par Rumpl

  I'm converting .flac and .mp3 audio files to .m4a using ffmpeg with libfdk_aac (Fraunhofer AAC encoder) like this :

  


  ffmpeg -i "001.flac" -c:a libfdk_aac "001.m4a"

  


  This works fine, but in case of .flac the resulting .m4a files include 0.046 seconds of silence at the start and sometimes a few extra milliseconds at the end. Though, I need the .m4a files to be of exactly(!) the same length without any extra silence. Is there a way to achieve this ?

  


  EDIT : At the moment I'm using an additional step, i.e. cutting the resulting .m4a file works at least in the beginning of the track, but there are still some (varying) extra ms in the end :

  


  ffmpeg -i 001.m4a -ss 0.047 -c:a libfdk_aac 001cut.m4a