Server: Remove thread limit when using ffmpeg

[ducthiem90]

I have a 4K video with hevc codec. I played it with caspar and obs studio. I ascertain that caspar don't use cpu best for decode, while obs studio is good. So caspar received late frame when obs studio play it smooth. I debuged and here is result:

• Caspar decode video time: 0.03s - 0.1s / frame
• OBS Studio decode video time: 0.02s - <0.04s / frame.
• Both caspar and obs studio use ffmpeg version 4.2.2.
  That is video for test: https://drive.google.com/open?id=1n0-DuFJo7qa-x1Pmn6y0QjFxGRXIunnG

[dotarmin]

@Julusian or @ronag, what do you say about this?

[ronag]

https://github.com/CasparCG/server/blob/master/src/modules/ffmpeg/producer/av_producer.cpp#L108

[dotarmin]

@ronag, v2.3.0 LTS or patch it later?

[ronag]

jsut remove i in 2.3

[ducthiem90]

I not sure it can fix problem. I will try it

[ducthiem90]

Oh. Problem at here:
https://github.com/CasparCG/server/blob/master/src/modules/ffmpeg/producer/av_producer.cpp#L125
Just remove it only

[ronag]

Oh. Problem at here:
/src/modules/ffmpeg/producer/av_producer.cpp@master#L125
Just remove it only

Removing that will increase the latency of some streams which is not appropriate. Should probably detect if it's not a live source and then let it auto pick threads.

[walterav1984]

https://github.com/CasparCG/server/blob/master/src/modules/ffmpeg/producer/av_producer.cpp#L108

This thread limit of 4 is this only in place for decoding or for the whole image preparation like de-interlacing, framerate conversion, chroma upsampling etc?

~Not sure if my issue is related but using casparcg server 2.3 commit 4176a9b on a unsupported ubuntu 20.04 (8core 2 * intel e5450 cpu and nvidia gtx640) shows no problems mixing 720p50 from the NDI producer to a PAL decklink consumer but a simple playback of a PAL dv codec videoclip on the same channel brings the system to stuttering/halt eventhough its load is around +-3.0 (cpu 40%) including the 720p50 ndi producer.~ Unrelated fixed by reducing channels from 3>2

[Julusian]

If I try commenting out that threads line or upping it to 32 I am still unable to play back the 4k files I have tried, with overall cpu usage of 14%.
But commenting out the line as @ducthiem90 suggests does allow it to play smoothly. So it looks like we need to decide on a rule to disable the slice threading

[ronag]

I'm fine with letting ffmpeg auto decide thread type. Remove that line.

[scriptorian]

Different codecs have different capability flags and may not support setting threads to auto.
I have added code to check the capability flags and where threading is supported but auto isn't I have set the default number of threads to the detected number of CPU cores. It is possible to set the decode threads from the configuration file with the key _ffmpeg/producer/threads_.

For clarity deinterlacing and so on mentioned above is done using FFmpeg filters. The filter is currently set to use 16 threads.

[walterav1984]

For clarity deinterlacing and so on mentioned above is done using FFmpeg filters. The filter is currently set to use 16 threads.

Thanks for explanation.