[Matroska-devel] PGS subtitle questions

Moritz Bunkus moritz at bunkus.org
Mon Nov 5 09:25:28 CET 2012


On Fri, Nov 2, 2012 at 5:05 PM, John Stebbins <stebbins at jetheaddev.com> wrote:

> Is there a "spec" for PGS in mkv?  I can't find anything helpful at http://matroska.org/technical/index.html
> If there is no spec, is there something that is considered reference code?  I've looked at mkvtoolnix so far.

That's all there is. There is no CodecPrivate, as you've pointed out
yourself, nor is that original image resolution not stored anywhere.

> Here's the problem I'm trying to unravel.  I have a HandBrake user that is complaining that when he scales down the
> video during transcoding, his player is not scaling the PGS subtitles appropriately.

At the moment Handbrake is doing nothing wrong. The information
required to scale the PGS just as much as the video it belongs to can
simply not be stored (properly). If that is required information in
order to show PGS subs properly then we should add Matroska elements
for it. Alternatively we could invent some kind of scheme for
CodecPrivate, but that would make all existing Matroska files with PGS
subs in them invalid.

Kind regards,

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