[Bug 797111] video-anc: Store width/height for which Closed Caption data was produced in the meta

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=797111

--- Comment #11 from Edward Hervey <bilboed at bilboed.com> ---
(Summary of discussion that happened offline)

Closed Caption are not "pixel-dependent" systems, therefore the width/height of
the underlying video doesn't matter per-se. What matters is:
* The *display* resolution (if it's rendered/overlayed)
* To a certain extent the aspect-ratio of the original material.

The information regarding the aspect-ratio is within the CDP stream (either not
specified and it's 16:9, or specified). For raw CEA 608 streams (non-CDP), it's
implied to be 4:3.

=> We don't *need* to store/provide the width/height of the original video
stream for a standalone CC stream.

So for storing CC in MOV, I would therefore recommend to just store in that CC
'trak' the same width/height as the correlated video stream.

(Out of scope, but put here for completion) For display/rendering, we should
use the *display* resolution/ratio (unrelated to underlying video stream) and
the original-aspect-ratio of the CC stream to figure out the ideal/optimal
rendering. But this is a similar problem to efficient rendering of other sub
formats.

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