Control: tags -1 - patch On 2020-10-26 13:19:36 +0000, Simon McVittie wrote: > Package: libtheora0 > Version: 1.1.1+dfsg.1-11 > Severity: normal > Tags: patch fixed-upstream > Forwarded: https://gitlab.xiph.org/xiph/theora/-/issues/2312 > > The latest version of Proton (Valve's branch of Wine, used to run Windows > games under Steam) runs in a Debian 10-based container > (Steam Runtime 2 'soldier'), instead of the Ubuntu 12.04-based > LD_LIBRARY_PATH library bundle (Steam Runtime 1 'scout') that was used > in previous releases. > > During the move from Steam Runtime 1 to 2, Proton developers noticed > a performance regression in their GStreamer-based video decoding, > which they were able to track down to the theoradec plugin. This plugin > uses libtheora, which has an optional feature called "telemetry" that > records statistics. It can be enabled or disabled at build-time; if > enabled at build-time, it is disabled by default at runtime. Activating > it at runtime involves setting some options, and incurs a significant > performance cost to convert each decoded frame from YUV to RGB for use > by Cairo (30-40ms per frame for 1920x1080 video). > > Note that despite its name, as far as I'm aware "telemetry" does not > send the statistics anywhere, it just captures them - so it isn't a > privacy problem, and is really just "-metry", with no "tele-" involved :-) > > In Debian, the telemetry feature is enabled in libtheora at build-time > since 1.1.1+dfsg.1-11, as requested in > <https://bugs.launchpad.net/ubuntu/+source/libtheora/+bug/627854>. > > GStreamer's theoradec plugin attempts to set the telemetry options to > user-specified values. However, in released versions of libtheora, > setting the telemetry options to any value - even 0 - is documented to > have the side-effect of enabling the telemetry feature and triggering > the performance regression. > > This can be fixed in three ways: > > 1. Disable telemetry at compile-time in libtheora. > We did this in the Steam Runtime as a temporary solution, but it's a > feature regression for libtheora, and the libtheora maintainers in > Debian presumably don't want that, so let's discard this option. > > 2. In GStreamer, if the telemetry options are set to 0, don't propagate > that into libtheora so that the expensive YUV -> RGB conversion is > not done, even with current releases of libtheora. This is > <https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/-/merge_requests/887> > and I've filed a separate Debian bug for it. The patch has been merged > upstream and was backported to 1.18.x (for 1.18.1, I think) in > <https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/-/merge_requests/892>. > > 3. In libtheora, if the telemetry options are all explicitly set to 0 > (for example by current versions of GStreamer), behave as though they > had not been set at all, and therefore don't enable the expensive > YUV -> RGB conversion. This is > <https://gitlab.xiph.org/xiph/theora/-/issues/2312> and > <https://gitlab.xiph.org/xiph/theora/-/merge_requests/4>, and is what > this bug report represents. The patch has been merged upstream for > v1.2.0, but there hasn't been an upstream release since 1.2.0 alpha 1 > (which doesn't have this change) in 2010, so it seems unlikely that > there will be a release with this change any time soon. FWIW, the upstream change does not apply to 1.1.1 and needs to be adapted accordingly. th_decode_packetin seems to be sufficently different that I leave that to someone with some deeper knowledge of the code. Cheers > > Following the principle that bad interactions between two components are > most robust if fixed on *both* sides, solutions 2 and 3 have both been > accepted upstream, and I suggest that they should also happen in Debian. > > The Steam Runtime maintainers will probably be doing a backport of this > into 1.1.1, so I'll try to send a patch later. > > Thanks, > smcv > -- Sebastian Ramacher
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