[Vorbis-dev] Enhanced Podcasts with Ogg Vorbis (Chapter Marks)

[Silvia Pfeiffer]

On Fri, Mar 30, 2012 at 2:47 AM, Georg Holzmann <grh at mur.at> wrote:
> Hallo again!
>
>
>> I've started the following wiki page:
>> https://wiki.xiph.org/Chapter_Extension
>
>
> I have one more feature request for the specification now ;)
>
> Many podcasters use not only chapter titles, but also append links to
> chapters (with MP4 files).
> Most of them just use one link, but in theory there could be more links as
> well ...
>
> This would be easy to include in the VorbisComment Chapter Extension by
> using a Tag CHAPTER001URL (or I guess there is a better name?)
>
> For example:
> CHAPTER001=00:00:00.000-->00:05:00.000
> CHAPTER001NAME=Chapter 1
> CHAPTER001URL=http://some.interesting.url.org/here.html
> CHAPTER002=00:05:00.000-->00:10:00.000
> CHAPTER002NAME=Chapter 2
> CHAPTER001URL=http://url.for.chapter.at/second.html
> ...
>
> As field names are not required to be unique, we could support multiple URLs
> per chapter as well:
> CHAPTER001=00:00:00.000-->00:05:00.000
> CHAPTER001NAME=Chapter 1
> CHAPTER001URL=http://some.interesting.url.org/here.html
> CHAPTER001URL=http://second.url.for.chapter.at/one
> ...
>
> Do you think that's reasonable ?

I think that would turn chapters into a really confused content track.
Think about it: chapters are there to provide navigation pointers to
people that come to the video. Now you're attaching outgoing pointers
to the incoming anchors. That's a very separate type of content and
requires rendering of the outgoing pointers and enable user
interaction. In particular if you want to enable more than one
hyperlink, how is that supposed to be rendered?

Instead, I would suggest to create actual content tracks, i.e. tracks
that have text or markup in them and have been built to be displayed.
The way that we recommend doing this are Kate tracks. You can author
them as SRT or KATE files (hopefully we will also support WebVTT at
some stage). You would author cues that align with your chapter
markers if necessary, but they don't have to, because the content will
be active as you're watching the video. This is in comparison to
chapter markers which are visible *before* you start watching the
video.


> Yes, and the final thing would be images for chapters ;) (or at some
> timepoints)

So, this is another issue altogether. If you want chapters displayed
for navigation purposes, but augmented with sample frames for the
chapters to give a visual indication of what one may jump into when
going to the chapter, then we have to add these representative images
to the chapters. Typically, they would be frames taken from the video.

It might be worth adding a CHAPTER001IMG field to our chapter
specification which allows inclusion of hyperlinks to images. If there
was a link directly into the video file to retrieve a frame, then that
link could be used.

Alternatively, that could be a base64 encoded image and inlined,
similar to how cover art can currently be included in VORBISCOMMENT
[1]. Maybe a field name of CHAPTER001BLOCKPICTURE for this?

I'm not sure which is better, actually. Opinions?

[1] http://wiki.xiph.org/VorbisComment#Cover_art


> AFAIK there is OggSpots or OggKate for that - do you know which way is
> supported by most of the players?

OggSpots is not for this purpose - it was suggested as a low bandwidth
"video" codec that just shows still images at certain times, but never
got implemented.
OggKate is for caption, karaoke and similar text tracks. You could put
hyperlinks into OggKate, but I believe it would just be rendered as
text by those players that understand OggKate. So, I'm not sure it
will solve your problem.

> Thanks again and have a nice weekend!

No worries.

Cheers,
Silvia.