Re: [FFmpeg-devel] [PATCH V2] lavc/libvpx: increase thread limit to 64

[James Zern <jzern-at-google.com@ffmpeg.org>]

On Tue, Oct 25, 2022 at 8:56 AM Dmitrii Ovchinnikov
<ovchinnikov.dmitrii@gmail.com> wrote:
>
> >> Why do you still impose an upper limit unconditionally even if the
> >>user has set his preferred number of threads?
> Libvpx-vp9 does not support number of threads greater than 64, so we impose
> an upper limit of 64.
> E.g. if we set it any higher we get the following execution error:
> [libvpx-vp9 @ 0x2f631c0] Failed to initialize encoder: Invalid parameter
> [libvpx-vp9 @ 0x2f631c0]   Additional information: g_threads out of range
> [..64]
> Error initializing output stream 0:0 -- Error while opening encoder for
> output stream #0:0 - maybe incorrect parameters such as bit_rate, rate,
> width or height
>

Deferring the check to libvpx should be fine and would mean less
maintenance of this wrapper if there are any changes made there.

> >>According to
> https://ffmpeg.org/pipermail/ffmpeg-devel/2018-November/236406.html the
> >>maximum of 16 has not been chosen because of H.264, but because there
> >>was some form of restriction in libvpx. Or at least there was belief in
> >>the existence of such a restriction.
> There is a restriction of maximum 64 threads, not 16.
>
> >>This code potentially calls av_cpu_count() twice.
> Can you please clarify how it calls it twice? Thanks.
>
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