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• How to label outputs inside the ffmpeg's process of transcoding for use them in mapping and in tee muxer ?

  20 juillet 2022, par youni

  I have a video, that consists of video stream and audio stream. I trancode it into two videos : 1920x1080 and 1280x720 with the same audio stream. I do not wish to transcode audio stream two times, I wish to use it twice with ffmpeg '-f tee' option. Now I need your support.

  


  This does not work :

  


  ffmpeg -to 00:00:10 -i /v \
  -map 0:v -an -vcodec libx264 -s 1920x1080 -b:v 4000k [VIDEO]\
  -map 0:v -an -vcodec libx264 -s 1280x720 -b:v 2000k [VIDEO2]\
  -f tee \
    -map [VIDEO] -map [VIDEO2] -map 0:a \
      -c:a mp3 -ab 42k \
        "[select='0,2':f=flv]1.mp4|[select='1,2':f=flv]2.mp4"
[NULL @ 0x55b7e2709340] Unable to find a suitable output format for '[VIDEO]'
[VIDEO]: Invalid argument


  


  My logic here was to label each output after -vcodec.. options and use these two labels in mapping and in tee muxer. Could you, please, advise what to do here ?

  


  This also does not work :

  


  ffmpeg -to 00:00:10 -i /v \
  -c:a mp3 -ab 42k \
    -filter_complex '[0:a]acopy[AUDIO];[0:a]acopy[AUDIO2]' \
  -map v -map [AUDIO] -vcodec libx264 -s 1920x1080 -b:v 4000k -f flv 1.mp4 \
  -map v -map [AUDIO2] -vcodec libx264 -s 1280x720 -b:v 2000k -f flv 2.mp4
ffprobe 1.mp4
ffprobe 2.mp4
  1.mp4: Stream #0:1: Audio: mp3, 48000 Hz, stereo, fltp, 42 kb/s
  2.mp4: Stream #0:1: Audio: mp3, 48000 Hz, stereo, fltp, 128 kb/s


  


  The result file 2.mp4 has default audio settings : 128 kb/s instead of 42 kb/s.

  


  My workable variant gives exactly correct result, but the process of transcoding is not optimized :

  


  ffmpeg -to 00:00:10 -i /v \
  -c:a mp3 -ab 42k -vcodec libx264 -s 1920x1080 -b:v 4000k -f flv 1.mp4 \
  -c:a mp3 -ab 42k -vcodec libx264 -s 1280x720 -b:v 2000k -f flv 2.mp4


  


  In this process ffmpeg transcodes audio stream twice, as I think. But I need to optimize this process and transcode audio stream once and use it twice with tee muxer. Could you say me, how to label outputs correctly as in my first code for use them in -map ?

  


• avformat/movenc : limit ISOBMFF AC-3 mapping to bsids <=8

  22 juin 2022, par Jan Ekström

  avformat/movenc : limit ISOBMFF AC-3 mapping to bsids <=8
  This leaves out RealAudio DolbyNet, which utilizes bsids 9 and 10,
  It is not clear whether the interpreted bit rate value (divided by
  
  2 or 4 depending on the variant), or the original bit rate value
  
  should be utilized to receive the bit_rate_code index.
  Signed-off-by : Jan Ekström <jan.ekstrom@24i.com>
  

  • [DH] libavformat/movenc.c

• avformat/matroskaenc : Remove duplicated code for writing WebVTT subs

  16 janvier 2022, par Andreas Rheinhardt

  avformat/matroskaenc : Remove duplicated code for writing WebVTT subs
  Up until now, the WebM variant of WebVTT subtitles has been handled
  
  specially : It had its own function to write it, because the data
  
  had to be reformatted before writing. But given that other codecs
  
  also need reformatting, this is no good reason to also duplicate the
  
  generic stuff for writing Block(Group)s.
  This commit therefore uses an ordinary reformatting function for
  
  this task ; writing WebVTT subtitles now uses the generic code
  
  and therefore automatically uses the least amount of bytes
  
  for its BlockGroup length fields whereas the earlier code used
  
  an overestimation for the length of the Duration element.
  
  This is the reason for the changes to the webm-webvtt-remux FATE-test.
  (This commit does not implement support for Matroska's way of muxing
  
  WebVTT ; it also does not add checks to ensure that WebM-style subtitles
  
  don't get muxed in Matroska. But the function for reformatting gets a
  
  webm prefix to indicate that this is for WebM.)
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavformat/matroskaenc.c
  • [DH] tests/ref/fate/webm-webvtt-remux