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I'm trying to compose two videos, and I'm using the alpha plug-in to make the white color transparent. To test the alpha plug-in I'm creating the pipeline with gst-launch.

The first test I done was:

gst-launch videotestsrc pattern=smpte75 ! alpha method=custom target-r=255 target-g=255 target-b=255 angle=10 ! videomixer name=mixer ! ffmpegcolorspace ! autovideosink videotestsrc pattern=snow ! mixer.

and it works great! Then I created two videos with those lines:

gst-launch videotestsrc pattern=snow ! ffmpegcolorspace ! theoraenc ! oggmux ! filesink location=snow.ogv
gst-launch videotestsrc pattern=smpte75 ! ffmpegcolorspace ! theoraenc ! oggmux ! filesink location=bars75.ogv

And changed the videotestsrc to a filesrc and it continues working:

gst-launch filesrc location=bars75.ogv ! decodebin2 ! alpha method=custom target-r=255 target-g=255 target-b=255 angle=10 ! videomixer name=mixer ! ffmpegcolorspace ! autovideosink filesrc location=snow.ogv ! decodebin2 ! alpha ! mixer.

However, when I use the video I want to compose, I'm not able to make the white color transparent:

gst-launch filesrc location=video.ogv ! decodebin2 ! alpha method=custom target-r=255 target-g=255 target-b=255 angle=10 ! videomixer name=mixer ! ffmpegcolorspace ! autovideosink filesrc location=snow.ogv ! decodebin2 ! alpha ! mixer.

Any idea what's happening? I'm using GStreamer 0.10.28.

You can download the test videos from here:

http://polimedia.upv.es/pub/gst/gst.zip

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1 Answer

I tested your approach, it works better than you think... just exchange the videos vice versa ;-)

gst-launch filesrc location=snow.ogv ! decodebin2  ! alpha method=custom target-r=255 target-g=255 target-b=255 angle=10  ! videomixer name=mixer ! ffmpegcolorspace ! autovideosink filesrc location=bars75.ogv ! decodebin2 ! alpha ! mixer.

Funny idea. Congrats!

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