[Matroska-devel] PGS subtitle questions
moritz at bunkus.org
Mon Nov 5 15:41:37 CET 2012
On Mon, Nov 5, 2012 at 3:06 PM, John Stebbins <stebbins at jetheaddev.com> wrote:
> I'm surprised that the matroska specification doesn't say something to
> the effect that unrecognized EBML id's should be ignored.
Oh it does. It it is implied.
> You would
> think this would be required for an extensible format. I would hope the
> majority of players are smart enough to skip unrecognized data since the
> only alternative is to choke and die. But I've seen plenty of hardware
> players that do exactly that when they see something unexpected. So I
> understand your point.
Unfortunately that's my experience as well (not directly by owning
said hardware, but judging from the multitude of support requests I
receive because players don't recognize tracks, don't recognize the
whole file, only show black pictures or freeze completely).
> I just did some checking to see if all this is really needed. I figured
> someone *must* have given this at least a little thought previously. It
> turns out there is a "video descriptor" required in the PGS subtitle
> data that defines the width and height "of the associated HDMV stream".
> So my request for original width and height is unnecessary.
> Now I'm rethinking this a little. Cropping information would still be
> helpful as a hint to a player about how to position the subtitles.
> Also, original pixel aspect ratio would be helpful in cases where the
> video has be anamorphically scaled during transcoding. I looked and
> found nothing about pixel aspects in the PGS data.
Is the "size of associated HDMV video track" stored inside the PGS the
coded pixels size or the display size?
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