[FFmpeg-devel] [PATCH] avfilter/vf_chromakey: The chromakey filter preserves non-opaque alpha transparency.

[Gavin Smith]

On 11/06/2020 22:03, Timo Rothenpieler wrote:
> On 11.06.2020 22:27, Gavin Smith wrote:
>> This is to address trac ticket #8724.  The filter did not preserve 
>> alpha transparency. Items that were transparent in the input would 
>> appear black on the output or pixels that were semi-tranparent would 
>> appear opaque.
>>
>
> What is the performance impact for inputs without an alpha channel?

Firstly, I'm new to this world of filters.  Now my patch only applies to 
chromakey and not chromahold. On that note, is it not the case that the 
chromakey mandates that all its inputs surfaces contain alpha (as per 
query_formats function)? Would any AVPixelFormat that does not match 
query_formats get converted to a format containing alpha transparency?

>
> Generally looks fine to me, but might need hidden behind an option, as 
> to not break existing setups that rely on this filter 
> discarding/ignoring the input alpha channel.

Yes. No problem. "preserve_transparency" and default to the equivalent 
of 'false'?

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