Add support for black background behind EIA-708 (ATSC) closed captions

[Clayton Smith <argilo@…>]

Currently, analog closed captions can be displayed in front of a black background for maximum contrast, but not EIA-708 (ATSC) captions. This patch adds support for a black background behind ATSC closed captions. When the black background option is turned on, captions appearing over light backgrounds are much easier to read.

[Clayton Smith <argilo@…>]

Add support for black background behind EIA-708 closed captions

[Clayton Smith <argilo@…>]

To enable the black background, go to Utilities/Setup? --> Setup --> TV Settings --> Playback OSD and enable the "Black background for closed captioning" setting on the third page. This setting previously applied only to analog captions, and I thought it made the most sense to generalize it to both analog and ATSC rather than adding in a new setting.

[danielk]

Clayton, CEA-708 allows the broadcaster to define both the foreground and background color, to implement this feature we should override both color choices in the 708 window, we don't want to end up using a dark background with a broadcaster's a dark foreground (intended to be on a light background). It would also be nice to be able to override the character outline, so instead of overriding the color one could just force characters to have a contrasting character outline (white for black characters, black for white characters, etc.)

Broadcasters do appear to have trouble sending out readable text, so I think this is a good feature to have. But we also don't want to make the text sent by more "with it" broadcasters to be harder to read.

[Clayton Smith <argilo@…>]

Force black background and white foreground

[Clayton Smith <argilo@…>]

Okay, I've changed the patch to force a white foreground when the black background option is turned on. It works well in my testing. Previously I was seeing grey text; now it's bright white and very readable. With the option turned off, everything is as before.

[danielk]

(In [23408]) Refs #7776. Render character background boxes.

[danielk]

(In [23409]) Fixes #7776. The patch was not correct, but it got me off my duff to fix this properly. The CCBackground setting is now respected by the CEA-708 caption renderer.