opencv: extracting video channels and depth from caps

[Sebastian Dröge]

On Sun, 2016-10-23 at 09:44 +0000, philippe renon wrote:
> Hi,
> 
> The opencv plugins has a utility method to extract the number of
> video channels and depth from caps (see code below).
> 
> Problem is that it fails for sparse formats (BGRx, ...) where it
> reports 3 channels of depth 8.
> For opencv to work correctly downstream, it should report 4 channels.
> 
> I can't find a simple way to detect that the caps/video info is
> sparse and has one additional "channel".

Should it actually use that additional "channel", it's containing
arbitrary and useless data.

In any case, you can get this info with e.g.
GST_VIDEO_INFO_COMP_PSTRIDE(), which will tell you 4 here (4 bytes to
get from one pixel to the next). It might even be better to directly
have a switch around the GstVideoFormat here instead.

-- 
Sebastian Dröge, Centricular Ltd · http://www.centricular.com
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