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• How to improve quality and latency in FFmpeg

  3 août 2020, par Andrew

  I'm trying to stream FFmpeg over the new SRT protocol that's supported as an output. For now though, I'm sending it in the form of FFmpeg -> UDP -> SRT -> SRT -> UDP -> MPV/FFmpeg.

  


  Somewhere along the line, the quality degrades sharply, and latency increases by quite a bit. This seemed to happen when adding audio. Meaning, if streaming just video, quality is decent and latency is low. If streaming just audio, quality is great but latency is high.

  


  Not sure where I'm going wrong with this, so any help would be appreciated. The main focus points is high quality low latency.

  


  ---

  


  Recording video through :

  


  ./ffmpeg.exe -rtbufsize 2147M -f dshow -i video="":audio="" -flush_packets 0 -preset medium -tune zerolatency -f mp4 -b:v 6M -g 30 -f mpegts udp://127.0.0.1:9001?pkt_size=1316


  


  or

  


  ./ffmpeg.exe -f dshow -analyzeduration 200k -probesize 6M -i video="":audio="" -flush_packets 0 -preset fast -tune zerolatency -b:v 5M -b:a 384K -c:a libopus -g 25 -f mpegts udp://127.0.0.1:9001?pkt_size=1316


  


  ---

  


  Then when taking it back at the receiver side, I use one of :

  


  ./ffmpeg.exe -i udp://127.0.0.1:9001 -c copy -bufsize 32M -f mpegts udp://127.0.0.1:9002?bitrate=26214400
./mpv.exe udp://127.0.0.1:9002


  


  or

  


  ./mpv.exe --no-cache --untimed --no-demuxer-thread --video-sync=audio --vd-lavc-threads=1 udp://127.0.0.1:9002


  


  ---

  


  What am I missing ? As is quality is generally terrible and latency can get up to 10 seconds. Is it just not possible with this set up ?

  


• Can any part of an ffmpeg command use expressions ?

  6 avril 2022, par corgrath

  I am still learning how expressions work with ffmpeg, whether any part of a command can be using expression or not.

  


  As an example, I have this command :

  


  ffmpeg -y -i input.mp3 -af "sofalizer=sofa=ClubFritz1.sofa:type=freq:radius=2:speakers='FL 45|FR 45|BL 45|BR 45'" output.mp3

  


  (The file CubFritz1.sofa can by the way be downloaded here)

  


  Which basically applies the sofalizer effect and specify that each channel should be heard / come from, the left side (45 degrees) of the audio.

  


  This works as expected.

  


  However, I cannot seem to get expressions working in the command at all.

  


  For example this :

  


  ffmpeg -y -i input.mp3 -af "sofalizer=sofa=ClubFritz1.sofa:type=freq:radius=2:speakers='FL if(0, 45, 45)'|'FR if(0, 45, 45)'|'BL if(0, 45, 45)'|'BR if(0, 45, 45)'" output.mp3

  


  Which does an if(0, 45, 45) as a test, so regardless the outcome should be 45, right ?

  


  However, when I run this command, it does not seem to work anymore, meaning the sound is not purely coming from the left side.

  


  I have even tried changing the location of the single ' in the command without luck :

  


  ffmpeg -y -i input.mp3 -af "sofalizer=sofa=ClubFritz1.sofa:type=freq:radius=2:speakers=FL 'if(0, 45, 45)'|FR 'if(0, 45, 45)'|BL 'if(0, 45, 45)'|BR 'if(0, 45, 45)'" output.mp3

  


  My question is, what are the rules for getting expressions working in an ffmpeg command ?

  


  How would the command be rewritten so that the if(0, 45, 45) works ?

  


• movdec : handle 0x7fff langcode as macintosh per the specs

  21 mars 2012, par Baptiste Coudurier

  movdec : handle 0x7fff langcode as macintosh per the specs
  The correct point that seperates ISO and MAC language codes is 0x400
  
  according to the current QT spec. Old QT specs did not list where this
  
  seperation is but apparently only defined the meaning of the first 137.
  

  • [DBH] libavformat/isom.c
  • [DBH] libavformat/mov.c