[FFmpeg-devel] [PATCH v2] lavc/ffv1: Properly check that the 4th and 5th quant tables are zeroes

[Michael Niedermayer]

On Sun, Jan 05, 2020 at 02:45:25PM +0000, Derek Buitenhuis wrote:
> Currently, the decoder checks the 128th value of the 4th quant table during
> while deriving the context on each sample, in order to speed itself up. This
> is due to relying on the behavior of FFmpeg's FFV1 encoder, in which if that
> value is zero, the entire 4th and 5th quant tables are assumed to be entirely
> zero.
> 
> This does not match the FFV1 spec, which has no such restriction, and after
> some discussion, it was decided to fix FFmpeg to abide by the spec, rather
> than change the spec.
> 
> We will now check whether the 4th and 5th quant tables are zero properly,
> by checking the 128th valye of both tables (which means they are zero due
> to the way they're coded in the bitstream).
> 
> For further context, the FFV1 issue in question is located at:
> 
>     https://github.com/FFmpeg/FFV1/issues/169
> 
> Signed-off-by: Derek Buitenhuis <derek.buitenhuis at gmail.com>
> ---
>  libavcodec/ffv1_template.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

LGTM

thx

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The educated differ from the uneducated as much as the living from the
dead. -- Aristotle 
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