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• How to create an encoding ladder for any aspect ratio ?

  18 avril 2024, par volume one

  For a given video uploaded by a user, I need to create three versions of it to cover standard definition (SD), high definition (HD), full high definition (FHD), and ultra high definition (UHD e.g. 4K). "resolution/encoding ladders" for standard aspect ratios like 16:9 and 4:3.

  


  For 4:3 we might have :

  


  640 x 480
960 x 720
1440 x 1080
2880 x 2160


  


  For 16:9 we might have :

  


  854 x 480
1280 x 720
1920 x 1080
3840 x 2160


  


  If a user uploads a file in either of those aspect ratios, we can create the four different versions because the resolution standards are known.

  


  However if a user uploads a video with an unforseen aspect ratio, say 23:19, then how would you go about formatting that video into SD, HD, FHD, and UHD versions ?

  


  If a 23:19 video is indeed uploaded then I am not looking to resize it to fit a different 'standard' aspect ratio. It must remain the same aspect ratio, but have four quality versions. The problem is what height and width sizes to create for non-standard resolutions ?

  


  I have already come accross many aspect ratios like 16:10, 21:9, 1.85:1, 2.39:1. How could I take care of making quality variations of those ?

  


  I am using Node.js and FFMpeg for video processing.

  


• ffmpeg filter_complex multiple overlays - why are they not syncing properly

  28 décembre 2023, par howdood

  I'm setting up live streaming using three overlaid inputs in ffmpeg. O:v is a webcam directly connected to the streaming box (a headless linux box) while 2:v and 3:v are ultra-low latency UDP streams from two remote R-Pis.

  


  The filter_complex argument I'm using (that works, with all three video inputs perfectly in sync) is
[0:v] fifo [v1] ;[2:v] fifo [v2] ; [3:v] fifo [v3] ;[v1]setpts=PTS-STARTPTS[sync1] ;[v2]setpts=PTS-STARTPTS[sync2] ; [v3]setpts=PTS-STARTPTS+5/TB [sync3] ;[sync1][sync2] overlay=x=W-w:y=H-h [out1] ;[out1][sync3] overlay=x=0:y=H-h [vfinal]

  


  Two questions about this :

  


  


  1. Why am I having to add +5/TB to [sync3] via setpts (in bold above) ? If I omit that, [3:v] is synced in to the stream noticeably ahead of the other two inputs. My best guess is that this may be to compensate for the processing time of the first overlay [sync1][sync2] which is introducing extra latency into that part of the stream. Is that right ?

     


  


  2. Importantly - the value of the extra pts compensation has to be dialed in by hand and will be specific to the underlying hardware used. Is there a way of getting ffmpeg to calculate this automatically so I don't have to worry about keeping in dialed in, in production ?

     


  


  


  Thanks for reading ! I'm at the limit of the ffmpeg docs here...

  


• How to use the hardware acceleration for ffmepg on m1-max ?

  10 février 2023, par ThoughtfulHacking

  Since there aren't m1 builds available from ffmpeg.org, I had to compile my own. Obviously, I'd like to get the best possible performance.

  


  

  • Does ffmpeg use the "Hardware-accelerated H.264" on the m1 max ?

  


  • Is there anything I need to do, like compiler flags, to get it ?

  


  • Any switch at run time ?

  


  • How can I verify that it's being used ?

  


  


  To compile ffmpeg, I just did the basics :

  


  ./configure --prefix=/tmp/ff       --enable-gpl --enable-nonfree   --enable-libx264
make
make install


  


  For x264, I just did
./configure —prefix=/tmp/ff
make
make install

  


  to run :

  


  ffmpeg -i random.wmv -c:v libx264 -preset ultrafast  -c:a aac  output-ultra.mp4 


  


  Anything else I should be doing ?