This allows to directly display RGB(A) movies without transcoding them
to YUV first. This allows the movie player to support APNG files (which
are supported natively by FFmpeg) with an alpha channel and without
converting them to YUV first.
This adds support for displaying subtitles embedded in movie files. This
supports files with multiple subtitle streams where each stream contains
the subtitles for one language. When the movie file is opened, the
stream for the currently active language will be used and displayed.
This resolves one of the points mentioned in #1522.
This also depends on PR #1484.