Commit 69b5aedc authored by Committed by Sebastian Dröge
videomixer2: Add transparent background option for alpha channel formats
This option allows the videomixer2 element to output a valid alpha channel when the inputs contain a valid alpha channel. This allows mixing to occur in multiple stages serially. The following pipeline shows an example of such a pipeline: gst-launch videotestsrc background-color=0x000000 pattern=ball ! video/x-raw-yuv,format=\(fourcc\)AYUV ! videomixer2 background=transparent name=mix1 ! videomixer2 name=mix2 ! ffmpegcolorspace ! autovideosink videotestsrc ! video/x-raw-yuv,format=\(fourcc\)AYUV ! mix2. The first videotestsrc in this pipeline creates a moving ball on a transparent background. It is then passed to the first videomixer2. Previously, this videomixer2 would have forced the alpha channel to 1.0 and given a background of checker, black, or white to the stream. With this patch, however, you can now specify the background as transparent, and the alpha channel of the input will be preserved. This allows for further mixing downstream, as is shown in the above pipeline where the a second videomixer2 is used to mix in a background of an smpte videotestsrc. So the result is a ball hovering over the smpte test source. This could, of course, have been accomplished with a single mixer element, but staged mixing is useful when it is not convenient to mix all video at once (e.g. a pipeline where a foreground and background bin exist and are mixed at the final output, but the foreground bin needs an internal mixer to create transitions between clips). Fixes bug #639994.
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