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• ffmpeg extract segment from video on-the-fly

  29 novembre 2022, par brunoais

  Context

  


  I want to make a service that hosts mp4 files but also provides video streaming.

  


  The server side is made of 2 "small" edge servers with capacity to cache about 0.1% of the content and one main server with a fraction of the bandwidth of the edge servers but much more robust storage.

  


  Recent status

  


  With the help of the ffmpeg manual,
  
Recently, when a segment is requested by an edge server, I run this command in ffmpeg

  


  ffmpeg -i in.mp4 -f hls -hls_list_size 0 -hls_playlist 1 -hls_time 60 -strftime 1  -hls_flags independent_segments+second_level_segment_index+second_level_segment_duration -hls_base_url '/path/to/file/' -hls_segment_filename 'name_%%03d.ts'  -c copy -copyts -hls_segment_type fmp4 out.m3u8


  


  Then obtain the requested segment (plus 3 subsequent ones) then delete everything.

  


  Current status

  


  Currently, I tried to get some level of optimization using -to :

  


  ffmpeg -i in.mp4 -to  -f hls -hls_list_size 0 -hls_playlist 1 -hls_time 60 -strftime 1  -hls_flags independent_segments+second_level_segment_index+second_level_segment_duration -hls_base_url '/path/to/file/' -hls_segment_filename 'name_%%03d.ts'  -c copy -copyts -hls_segment_type fmp4 out.m3u8


  


  Then sending the requested segments to the edge that requested them, then delete the result.
Do note that /path/to/file/ is a tmpfs with quite modest capacity (files can't stay there for too long).

  


  The current setback

  


  The main issue I get with the current process is that it takes a long time to obtain the last segments (2-4s).
That creates a bottleneck in how long segments take to be served. I can increase the buffer from 3 videos to 5 (or even more) but that doesn't solve the actual problem and, instead, will bring more strain on other areas.

  


  Cutting is not reliable

  


  There doesn't seem to exist an option to select what segments to generate using ffmpeg.

  


  Using cutting argument for start time (-ss) has shown to usually work but regularely causes the first keyframe used to be wrong. However, I believe I have all segment files in variable length and cut at the keyframe of the original file.

  


  Help needed

  


  How to extract an arbitrary segment of an mp4, described in the m3u8 file (which was done in a previous extraction) ?

  


  I have full control over ffmpeg and I can automate edits to the m3u8 file after generating them, as required. However, I need to understand and see how can this be solved.

  


• Merge commit ’b8d2630c5327d2818d05c8a48be0417905d8e0fd’

  11 mai 2015, par Michael Niedermayer

  Merge commit ’b8d2630c5327d2818d05c8a48be0417905d8e0fd’
  * commit ’b8d2630c5327d2818d05c8a48be0417905d8e0fd’ :
  
    dashenc : Reduce the segment duration if cutting out parts with edit lists
  Merged-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavformat/dashenc.c

• Revision 6522 : $GLOBALS[’liste_des_forums’] a disparu

  12 juin 2012, par kent1 — Log

  $GLOBALSliste_des_forums ? a disparu