[ogg-dev] Skeletal relations

Shane Stephens shane.stephens at gmail.com
Wed Feb 20 12:57:50 PST 2008

Hi again :)

On Wed, Feb 20, 2008 at 9:01 PM, ogg.k.ogg.k at googlemail.com <
ogg.k.ogg.k at googlemail.com> wrote:

> > 1) Font data, as in the actual font itself, doesn't really belong in an
> ogg
> > stream.
> People wanting to  have more control on the appearance of an overlay
> might want to control the font. Since font naming is largely non standard
> (eg, the foundry etc system (you know, *-*-*-* system) is X only I think,
> and I think Windows just has filenames), one can't specify a font to use
> in a way that you know will work. Provided you'd have the font in the
> first place. That's (one of ?) the reason various document types can have
> embedded fonts. Yes, it's not ideal, but there's no real other way to do
> it that I know of.

If you have an application-specific need for exact font data, then I think
the mechanism for retrieving this data should lie in your application, and
not in the media format that you're using for media data.  I would have said
the same thing to Adobe if they'd asked me ;-)

> > 2) We have been working on a specification and mechanism for indicating
> to
> > clients that there are multiple tracks of the same "kind" (e.g.
> > translation), and allowing clients to request individual tracks out of
> sets
> > of like tracks.  In fact with HTTP headers like Content-Language we can
> also
> > allow the server to default to a particular translation selection in the
> > absence of guidance from the client.  At the moment I think a
> preliminary
> > name for this specification is ROE - Silvia is in the process of nailing
> the
> > spec down so you should ask her any questions you have about it :)
> > Obviously this doesn't "solve" the duplication issue (if there is one)
> but
> > it does prevent duplicated data eating bandwidth.
> In this case, it's realtime muxing. That's a special case. While it
> probably does
> help in a lot of situations, it doesn't apply in all cases where one could
> use
> an Ogg stream. It's a great help though.
> Besides, when I coded the xine Kate plugin, I've made it so you can switch
> languages on the fly. All streams are decoded, but only the selected one
> (if any) is actually displayed.  This is not possible with such a scheme
> (not
> saying it's deficient, just that it also adds constraints).

Realtime vs. prerolled do not present problems here. ROE is agnostic as to
whether the media data is generated on the fly or stored on disk - it merely
needs a handle on the data.  Furthermore, with Annodex and ROE we will
absolutely be able to switch tracks on the fly - that's part of the point of
time-based URI values.  Furthermore we can do so without the overhead of
transmitting and decoding multiple (text / audio / video / whatever) tracks
at a time.  This is not a special case that we haven't considered :)

> > 3) Text is cheap!  Really cheap :)  Seriously - compare the amount of
> space
> > in your file taken up by text to that taken up even by audio, let alone
> > video.
> Yes, text is cheap, but not fonts. Especially if they have to be burst
> transmitted
> in headers before playback actually begins. It's also a corner case
> (custom
> font + lots of multiplexed streams). but I'd ideally like to have
> something that
> scales if possible.
> Speaking of scaling, one of the issues that I've seen is the large amount
> of
> framing data against codec data. Since I have a packet per page (for
> timing
> reasons), Ogg adds a lot of bytes to mine. But that is another story...

Fonts are not cheap.  That's true.  Again, though, I think that a
font-retrieval mechanism is outside the scope of Ogg, and should be dealt
with in an application-specific way (we would all obviously prefer a
consistent font naming scheme over all operating systems, but that's not
going to happen).

By the way, how would you deal with fonts if you didn't burst transmit
them?!  You can hardly decode them as a stream...

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