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• How do I encode a video stream to multiple output formats in parallel with ffmpeg ?

  21 juillet 2022, par rgov

  I would like to use one FFmpeg process to receive video input and then pass that video to multiple separate encoder processes in order to efficiently make use of all available CPU cores.

  


  The FFmpeg wiki article on Creating multiple outputs has this note from @rogerdpack :

  


  


  Outputting and re encoding multiple times in the same FFmpeg process will typically slow down to the "slowest encoder" in your list. Some encoders (like libx264) perform their encoding "threaded and in the background" so they will effectively allow for parallel encodings, however audio encoding may be serial and become the bottleneck, etc. It seems that if you do have any encodings that are serial, it will be treated as "real serial" by FFmpeg and thus your FFmpeg may not use all available cores. One work around to this is to use multiple ffmpeg instances running in parallel, or possible piping from one ffmpeg to another to "do the second encoding" etc. Or if you can avoid the limiting encoder (ex : using a different faster one [ex : raw format] or just doing a raw stream copy) that might help.

  


  


  The article has an example of using a tee pseudo-muxer, but it uses "a single instance of FFmpeg. The example of piping from one instance of FFmpeg to another only allows one encoder process.

  


  A 10-year-old version of the same article mentions using the tee process but it was subsequently deleted :

  


  


  Another option is to output from FFmpeg to "-" then to pipe that to a "tee" command, which can send it to multiple other processes, for instance 2 different other ffmpeg processes for encoding (this may save time, as if you do different encodings, and do the encoding in 2 different simultaneous processes, it might do encoding more in parallel than elsewise). Un benchmarked, however.

  


  


  Along the same lines : Some of the example commands use the mpegts to encapsulate frames before passing them between processes. Is there any constraint that this applies to the codecs or types of metadata that can be sent to downstream processes ?