[libav-api] Packed RGB formats missing from libav

wm4 nfxjfg at googlemail.com
Thu Sep 10 21:34:26 CEST 2015


On Sun, 6 Sep 2015 16:25:47 +0200
Luca Barbato <lu_zero at gentoo.org> wrote:

> 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.

Sure, feel free to add an alpha_type field to AVFrame or so.


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