[gst-devel] Conversion to ARGB32

Zack Rusin zack at kde.org
Tue Apr 11 11:28:02 CEST 2006

On Tuesday 11 April 2006 10:16, you wrote:
> Your problem is that you're asking ffmpegcolorspace to add an alpha
> channel, which it won't do. It will transform from one colorspace
> that has an alpha channel to a different one, but it won't add a
> random alpha channel to an existing video - you need the 'alpha'
> element for that. 

Hmm, interesting, are you sure about that? The non-existence of an alpha 
channel in all conversion software I've seen implies opaque color. 
I was looking at ffmpegcolorspace/imgconvert.c and the conversion table 
has both 
{PIX_FMT_YUV420P, PIX_FMT_RGBA32, yuv420p_to_rgba32},
{PIX_FMT_YUV420P, PIX_FMT_BGRA32, yuv420p_to_bgra32},
which has me a little confused.

> But - since this indicates that your incoming video 
> doesn't have an alpha channel anyway, you could also just ask
> ffmpegcolorspace to convert to 24bpp,32depth, which is RGB packed
> into 4 bytes, but the alpha channel will be random.

Thanks. I just tried it, unfortunately with the same result. In case 
you'd like to look at it, a minimal example app is at:


job Placement, n.: Telling your boss what he can do with your job.

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