# codecalpha

This plugin contains a set of utilities that helps handling alpha encoded streams as produced by some WebM streams using VP8/VP9. The elements are meant to be used in decoder wrappers which allows playbin to automatically handle these streams.

`codecalphademux` will produce two streams out of a stream of buffers holding the GstVideoCodecAlphaMeta. The presence of the meta is indicated by the usage of the field `codec-alpha=(boolean)true` in the caps. This is only applicable to VP8 and VP9 for now.

Wrappers for vp8dec and vp9dec are available, allowing seamless support for these streams inside playbin (which is used by WebKit GTK and WPE).

(from GStreamer Bad Plug-ins)

Name | Classification | Description
--- | --- | ---
alphacombine | Codec/Demuxer | Use luma from an opaque stream as alpha plane on another
codecalphademux | Codec/Demuxer | Extract and expose as a stream the CODEC alpha.
vp8alphadecodebin | Codec/Decoder/Video | Wrapper bin to decode VP8 with alpha stream.
vp9alphadecodebin | Codec/Decoder/Video | Wrapper bin to decode VP9 with alpha stream.

Subpages:

alphacombine – Use luma from an opaque stream as alpha plane on another

codecalphademux – Extract and expose as a stream the CODEC alpha.

GstAlphaDecodeBin

vp8alphadecodebin – Wrapper bin to decode VP8 with alpha stream.

vp9alphadecodebin – Wrapper bin to decode VP9 with alpha stream.

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