[libav-api] Packed RGB formats missing from libav

Luca Barbato lu_zero at gentoo.org
Sun Sep 6 16:25:47 CEST 2015


On 04/09/15 19:34, wm4 wrote:
> On Fri, 4 Sep 2015 02:42:29 +0200
> Luca Barbato <lu_zero at gentoo.org> wrote:
> 
>> On 03/09/15 17:28, Patric Schmitz wrote:
>>> So, how would I go from here?
>>
>> Check for their presence and do not add them in the case.
>>
>>> Does libav use other identifiers for those formats which I could use,
>>> and which are present in libav as well as ffmpeg? What's the specific
>>> reason those formats are not supported?
>>
>> Those formats are a shorthand for "RGBA with A ignored so is fine to
>> leave it as 0", used to avoid fitting the alpha channel with 255 in
>> formats that do not really support alpha...
> 
> They also signal whether the decoder output includes an alpha channel
> or not. With FFmpeg you know from the pixel format, with Libav you
> have to guess. I've brought this up before.

If a codec does not use the alpha channel and it is still outputting
RGBA the alpha should be set to max whichever is the max...

Fitting that kind of information in the enum isn't exactly great. You
know quite well that I (and Kostya) want to transition away from that model.

lu


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