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• Generate MPEG-DASH segments when requested [closed]

  16 septembre 2024, par John Smith

  Up front disclaimer : this question is almost identical to the one here : Generate single MPEG-Dash segment with ffmpeg but it seems that ffmpeg has updated over time and now the answer provided by Coumeu is no longer accurate.

  


  Using ffmpeg, I am attempting to "lazily create" the segments needed for MPEG DASH playback. I have a static manifest (MPD) which includes SegmentTemplates for 1 video and 1 audio stream.

  


  Only when the endpoints provided in the SegmentTemplate for init or media segments is hit it will generate this segment. In other words, nothing is processed up front.

  


  I am creating the init segment using the following movflags :

  


  +frag_keyframe+faststart+skip_trailer 


  


  I am creating the media segment using the following movflags

  


  +frag_keyframe+default_base_moof+delay_moov+skip_trailer+dash+global_sidx


  


  and the following additional commands any segment type :

  


  -map_metadata -1 -copyts -start_at_zero -map 0:${streamIndex}


  


  This results in playable video with the correct duration, but it seems to be switching fragments quite fast. On average one fragment per second. When I omit the delay_moov flag, the video also starts glitching, like it's stepping over I-Frames.

  


  My observations when I look at the boxes :

  


  

  • earliest_presentation_time (sidx box) is 0 for all segments

  


  • base_media_decode_time (moof->traf->tfdt box) is 0 for all segments

  


  


  I'm looking for either the correct command line to create segments on the fly, or hacky ways to get it done right if ffmpeg doesn't provide it out of the box. Even information about what to look for would be helpful, because my knowledge about mp4 and MPEG-DASH is running out.

  


• Reduce the number of chunk-stream files when converting to mpeg-dash

  10 juillet 2024, par NSS

  My command : ffmpeg -i input_file.mp4 -c:v libx264 -c:a aac -b:v 6000k -b:a 192k -f dash output.mpd

  


  When I convert a mpeg4 file into mpeg-dash, ffmpeg generates a certain number of .m4s files (e.g chunk-stream0-00003.m4s) of different sizes. If I convert a really large file ffmpeg can generate thousands of files like that. My questions are :

  


  

  1. how can I set that no .m4s file is more than 5MB ? I need this to stream a smaller chunk faster over HTTP.

  


  2. how can I reduce the number of generated .m4s files ? I need this because the custom storage has a limit on files in a directory.

  


  


• A/V out of sync when using ffmpeg from mpeg-ts to dash

  17 mai 2018, par user3540646

  I’m using ffmpeg in order to convert MPEG-TS stream to MPEG-DASH.
  The mpeg-ts is h264 and aac_latm.
  Therefore I don’t need to reencode the video.
  The command I use :

  ffmpeg -i http://10.0.0.211:55555/Ch%2011%20Kan -strict -2 -c:v copy -window_size 10 -extra_window_size 10 -use_template 1 -use_timeline 1 -f dash kan.mpd

  I’m copying the video codec by using -c:v copy and the audio codec is default to aac.

  That way I get DASH stream BUT the audio/video is out of sync !

  How can I fix it ?

  Notes :

  1. If I reencode both audio and video like :

     ffmpeg -i http://10.0.0.211:55555/Ch%2011%20Kan -strict -2 -window_size 10 -extra_window_size 10 -use_template 1 -use_timeline 1 -f dash kan.mpd

  Then the audio/video is synced perfectly.
  But I do not want to reencode the video for nothing as I mentioned the video is already h264. (directly impact to performance)

  2. If I convert the MPEG-TS stream to mp4 file like :

     ffmpeg -i http://10.0.0.211:55555/Ch%2011%20Kan -strict -2 -c:v copy kan.mp4

  Then the audio/video is synced perfectly.