[Matroska-devel] PGS subtitle questions

John Stebbins stebbins at jetheaddev.com
Mon Nov 5 13:35:12 CET 2012

On 11/05/2012 09:25 AM, Moritz Bunkus wrote:
> Hey,
> 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.

In order to not invalidate existing streams, you could make the new
element (or codec private data) optional and only necessary when scaling
of PGS by the playback software is desired.  Players that don't support
it would hopefully just ignore it.

I have no preference for whether it is a new element or codec private
data.  But since there is already a format for vobsub that has the
necessary information, would it be a good idea to reuse that format? 
The only part that wouldn't be relevant is the palette.  The rest could
actually be useful I believe.

More information about the Matroska-devel mailing list