[FFmpeg-devel] [PATCH 1/3] avcodec/encode: add checks for custom inter/intra/chroma matrices

[Marton Balint]

On Thu, 9 Jan 2025, Michael Niedermayer wrote:

> Hi
>
> On Tue, Jan 07, 2025 at 12:08:39AM +0100, Marton Balint wrote:
>> All elements should be within 1-255.
>> ---
>>  libavcodec/encode.c | 16 ++++++++++++++++
>>  1 file changed, 16 insertions(+)
>
> this breaks:
>
> ./ffmpeg -i lena.pnm -qscale 4 -intra_matrix 10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10 -chroma_intra_matrix 400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400 -bitexact custommatrix10,400.jpg
>
> I have not double checked the spec, but the resulting file worked fine
> before the patch

Hmm, apparenly JPEG does not write directly the matrices to the file but 
the qscale corrected variants, so values larger than 255 can be OK. And 
even if there is an overflow, it uses clipping, so any positive value 
seems OK there.

I will rework this and use a codec specific check instead of a generic 
one...

Regards,
Marton

>
> thx
>
> [...]
>
> -- 
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> He who knows, does not speak. He who speaks, does not know. -- Lao Tsu
>