[FFmpeg-devel] [PATCH] fate/pixfmt: disable dithering in the scale filter

[James Almer]

On 11/8/2024 9:03 PM, Michael Niedermayer wrote:
> On Fri, Nov 08, 2024 at 04:56:38PM -0300, James Almer wrote:
>> On 11/8/2024 5:15 AM, Martin Storsjö wrote:
>>> On Thu, 7 Nov 2024, James Almer wrote:
>>>
>>>> Should fix fate failures across different systems.
>>>>
>>>> Signed-off-by: James Almer <jamrial at gmail.com>
>>>> ---
>>>> This only hides the bug in the dither path for unscaled planar yuv
>>>> 8bit to
>>>> hbd and vice-versa.
>>>> Someone more familiar with the code should check what exactly is
>>>> going on.
>>>
>>> LGTM, thanks! Good job in hunting this one down - it seems odd as the
>>> exact output value seems stable on each machine (and valgrind doesn't
>>> find any nondeterminism), but the output is different on most machines.
>>
>> The only tests that fail are those using the DITHER_COPY method in
>> planarCopyWrapper() when dither is used, and the only difference compared to
>> the no dither path is accessing the "dithers" static const array defined in
>> the same file.
>> Maybe compilers are doing something weird when aligning it, or accessing it?
> 
> Not sure i fully understand but the brute force way to debug this is maybe
> just add a printf() to dump every value then diff between to see where differences
> start.

I can't even reproduce the issue locally, so...

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