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• Fragmented MP4 : TrackFragHeader TFHD must have TrackID, is this in the spec ?

  27 juillet 2021, par Penquin

  I'm building a fragmented mp4 muxer and noticed that the track id is repeated inside the TFHD.
If the video does not have this undocumented track id, it will simply not play.

  


  Here's an example of a muxer adding it :
https://github.com/edgeware/mp4ff/blob/bb9320744777dc97f18034c8aed45a9bcdbaa995/mp4/tfhd.go#L154

  


  I was relying on the open spec provided by Microsoft :
https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-sstr/513ea48c-9a57-4792-a32a-fb6202ce2a58

  


  Is this an addition to the spec ? Is the spec provided by Microsoft wrong ?

  


• ffmpeg subtitles alignment and position

  7 mai 2024, par friendlygiraffe

  I am adding subtitles to a video using :

  



  ffmpeg -i "imput.mp4" -lavfi "subtitles=subtitles.srt:force_style='OutlineColour=&H100000000,BorderStyle=3,Outline=1,Shadow=0,Fontsize=18'" -crf 1 -c:a copy "output.mp4"


  



  Which results in :

  



  

  



  I am repositioning this using Alignment :

  



  ffmpeg -i "imput.mp4" -lavfi "subtitles=subtitles.srt:force_style='Alignment=9,OutlineColour=&H100000000,BorderStyle=3,Outline=1,Shadow=0,Fontsize=18'" -crf 1 -c:a copy "output.mp4"


  



  

  



  But according to the Line-Alignment ASS Tags docs, there are only 9 positions. 1 : Bottom left, 2 : Bottom center, 3 : Bottom right, 5 : Top left, 6 : Top center, 7 : Top right, 9 : Middle left, 10 : Middle center, 11 : Middle right

  



  Is there a way to tweak this positioning ?

  



  I want the subs to be left-aligned, but lower down. Like this :

  



  

  


• Using ffmpeg to stream to Facebook Live Video : can preview, but not go live

  17 novembre 2016, par Einar Magnússon

  I am trying to stream a webpage to Facebook Live video using ffmpeg. I know I can use OBS, but I’m trying to do it from a server, so I can’t go with OBS. It works fine when I’m previewing, but as soon as I press ’Go live’, at first it seems like it’s starting, but then when it takes me to the live view it just says that the video has ended. I even checked the error of the video log using Graph API, nothing. I’m using PhantomJS to pipe screenshots to ffmpeg :

  phantomjs phantom.js | ffmpeg -y -c:v mjpeg \
  
  -f image2pipe \
  
  -r 5 -i \
  
  - -c:v libx264 \
  
  -x264-params keyint=5 \
  
  -b:v 1000k -minrate 1000k -maxrate 1000k -bufsize 500k \
  
  -f flv 'rtmp://rtmp-api.facebook.com:80/rtmp/xxxxxxxxxxxxxxxx'

  As I said, it’s working fine in the preview of the live stream on Facebook, but just ends immediately when I go live. I added the bitrate options to try to keep a constant bitrate as mandated by Facebook (https://developers.facebook.com/docs/videos/live-video/production-broadcasts), and I have a keyframe every 5 frames (rather low frame rate at 5fps) so that requirement is fulfilled as well.

  I’m not sending any audio, could that cause a problem ?