[vlc-devel] [PATCH] Add support for rendering EIA-608 captions with a black background

Devin Heitmueller dheitmueller at kernellabs.com
Wed Jan 2 21:25:11 CET 2013

On Wed, Jan 2, 2013 at 2:55 PM, Laurent Aimar <fenrir at elivagar.org> wrote:
>  I don't think that forcing CC to always use a black background to be a good
> thing.

This would actually be completely consistent with the expectations of
EIA-608 users.  Hearing impaired individuals using closed captions
*expect* them to be rendered on a black background.

The protocol also allows the broadcaster to use different color
backgrounds, and this approach paves the way to allow that
functionality (by converting the "render_bg" property into a field
which specifies an actual color).  Right now it's restricted to black,
which is the color the spec explicitly says to use if not supporting
the feature to change to different colors.  But support for other
colors could certainly be added in the future.

> But adding an option to the CC decoder doesn't fell right either.
>  Wouldn't it be possible to simply do it automatically in the freetype module
> without the CC decoder requesting it (it would probably need another configuration
> item in the freetype module)?

My motivation behind having the CC decoder request the feature
explicitly was to ensure not to interfere with other subdec modules.
I'm not against having all the subdec modules use this functionality
at some point, but I am not in a position to test it.

> This way it would be consistant with all text subtitles.

My goal is not to be consistent with how VLC does subtitles for other
formats.  My goal is to be consistent with what consumers of EIA-608
subtitles expect across devices/applications (whether it be VLC,
televisions, or other applications which render closed captions for
the hearing impaired).  I'm modifying the decoder to conform to the
FCC specifications related to EIA-608 captions so that products
including VLC which are sold in the United States are in compliance.


Devin J. Heitmueller - Kernel Labs

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