Re: [FFmpeg-devel] [PATCH] avcodec/libx265: Don't copy A53 closed captions by default

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Tomas Härdin:
> tis 2024-06-11 klockan 10:05 +0200 skrev Andreas Rheinhardt:
>> Tomas Härdin:
>>> tis 2024-06-11 klockan 09:42 +0200 skrev Andreas Rheinhardt:
>>>> The SEI handling of libx265 is buggy and can easily lead
>>>> to memory corruption: It reuses certain buffers, but when
>>>> reusing them it presumes that it is enough for these buffers
>>>> to exist and does not check whether they are actually large
>>>> enough to hold what is intended to be stored in them.*
>>>>
>>>> Our users are exposed to this because forwarding A53 CC data
>>>> is enabled by default. Change this to make it disabled
>>>> by default.
>>>>
>>>> "Fixes" tickets #9666, #10411, #11052 and (presumably) #10906.
>>>
>>> Shouldn't users use non-buggy versions of libx26? I've had people
>>> ask
>>> about CC, and I'm sure many users would be annoyed at them suddenly
>>> breaking. I suggest complaining loudly at compile time and/or when
>>> loading libx265 instead
>>
>> Non-buggy versions of libx265? People use what they have because it
>> exists.
> 
> What I'm getting at is that this is libx265's responsibility, and the
> responsibility of packagers not to ship broken versions of it. Does all
> A53 CCs break with the present libx265 bug or only some?
> 

1. There is no version of libx265 with this bug fixed (the bug itself is
here:
https://bitbucket.org/multicoreware/x265_git/src/8787e87020d77416f0ff0b7f3c97ac8b90332c31/source/encoder/encoder.cpp#lines-1086:1117)
2. The issue can happen when a later frame uses larger SEIs or more SEIs
than an earlier frame. Because x265 thinks that every buffer that exists
can handle an arbitrary amount of data.

- Andreas

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