Support SMT/HT when decoder threads number is set to auto?

Feature requests for VLC.
zypA13510
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Support SMT/HT when decoder threads number is set to auto?

Postby zypA13510 » 10 Mar 2024 16:08

I have a lot of 1080p60 lossless videos encoded with ffv1/flac. VLC fails to decode these files in real time, the playback is stuttering constantly.
Then I found that VLC is only using 50% of my CPU. And when I increase the thread count (was 0, I suppose that means auto?) of FFmpeg decoder in advanced settings, the video can actually be played back smoothly.
Thus I suspect that VLC is only using 1 thread per core, rather than 2, which explains the 50% CPU usage.
Most modern applications will actually recognize SMT (simultaneous multithreading) / HT (hyperthreading) capability and double the thread count. Why wouldn't VLC do this by default?

Rémi Denis-Courmont
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Re: Support SMT/HT when decoder threads number is set to auto?

Postby Rémi Denis-Courmont » 12 Mar 2024 04:12

0 is automatic, meaning it will use the minimum of the number of physical threads and a fixed value ((16, IIRC).

Beware that not all video codecs can be threaded though.
Rémi Denis-Courmont
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