[Bug 685282] dvdspu: figure out how to make it work with hardware decoders and subpicture overlays

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=685282

--- Comment #36 from Jan Schmidt <thaytan at noraisin.net> ---
I think somewhere down the road, it would be nice to have more generic SPU
interface than sending all these events with application/x-gst-dvd prefix, but
I'm not sure what that API should be.

So far these patches look good.

I'm still a little worried about the performance impact blending an entire
display-area sized region. My memory is that it was a non-trivial impact in
2004-2005 when I wrote the original code. It's something we could optimise
later though - perhaps keep an auxilliary array of "height" entries that stores
the X position of the first non-transparent pixel for each line so it can skip
blending.

Instead of only scaling down to fit, is it worth considering using the
set-frame-size event to allocate a larger downstream frame as the target for
blending into? I think in any case a mechanism for communicating the intended
display size to the sinks would be useful when using
GstVideoOverlayComposition.  I have a rip here where the video was originally
1080p, and they've trimmed the black-bars to enode 1920x800. When the black
bars are added back in for display, the PGS titles should appear there -
starting below Y=870 or so.

Between dvbsuboverlay, dvdspu and textoverlay, we probably have enough
experience to start factoring out a set of common overlay/SPU behaviours into a
base class and have features like negotiation, colour conversion and software
blending fallbacks in there.

Besides all that, there is something wrong with these patches, but I don't know
what yet. On my Back To The Future DVD, they make it not display certain
subpicture entries in the bonus 'Animated Anecdotes' track, but only some.

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