Is videoscale affecting alpha value?

[Sebastian Dröge]

On Fr, 2013-12-20 at 02:08 +0100, Peter Maersk-Moller wrote:
> Hi
> 
> I've come across a problem with alpha values where videoscale in some cases
> seems to affect the alpha value in a not so good way for GStreamer 1.2.0
> (and 1.2.1) in a way that was not the case for version 0.10.
> 
> When using the following pipeline, the alpha value of each pixels gets set
> to 127, if the content decoded is not 1280x720 and set to 255, if the
> content is 1280x720:
> 
> /usr/local/bin/gst-launch-1.0 -v filesrc location=../test/pmm2.mp4 !\
>     decodebin !\
>     videoscale !\
>     videoconvert !\
>     'video/x-raw, format=(string)BGRA, width=(int)1280, height=(int)720' !\
>     shmsink socket-path=/tmp/feed1-control-pipe shm-size=50000000
> wait-for-connection=0

What's the video format that is output by decodebin here? Does it
contain an alpha channel already, and what's the size of the input
video? Please paste the complete output of gst-launch-1.0 -v in good
(alpha=255) and bad (alpha=127) cases.

Can you produce a more simple test case that does not involve shmsink
and a file, or can you make the file available?

-- 
Sebastian Dröge, Centricular Ltd - http://www.centricular.com
Expertise, Straight from the Source
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