Re: [FFmpeg-devel] [PATCH] lavc/vvc: Invalidate PPSs which refer to a changed SPS

From: Christophe Gisquet <christophe.gisquet@gmail.com>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Cc: Frank Plowman <post@frankplowman.com>
Subject: Re: [FFmpeg-devel] [PATCH] lavc/vvc: Invalidate PPSs which refer to a changed SPS
Date: Sat, 15 Jun 2024 08:34:54 +0200
Message-ID: <CAPYFPM3jYrjSbeqpS0MvpU=Wu9CxFxyzHfQSoKgGjyBtLtfF7A@mail.gmail.com> (raw)
In-Reply-To: <20240614093903.98716-1-post@frankplowman.com>

Le ven. 14 juin 2024, 11:39, Frank Plowman <post@frankplowman.com> a écrit :

> When the SPS associated with a particular SPS ID changes, invalidate all
> the PPSs which use that SPS ID.  Fixes crashes with illegal bitstreams.
> This is done in the CBS, rather than in libavcodec/vvc/ps.c like the SPS
> ID reuse validation, as parts of the CBS parsing process for PPSs
> depend on the SPS being referred to.
>

I am uncertain about this. I have no definite knowledge nor proof, but I
would have thought these are persistent, IE it's legal to update some of
them, their validity depending on something else.

Wondering if the tested streams are thus conformant.

But I don't know the actual rule. Maybe finding an EOB/EOS NUT? Related to
some particular shape of a clean random access point, that would require
retransmitting VPS/SPS/PPS/APS/... ?

Asking Benjamin Bross might be a better option here.

>
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