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

[Georg Holzmann]

Hallo Sivlia, Martin!

 > Somebody (perhaps Georg) suggested this a
 > few weeks ago at:
 > https://wiki.xiph.org/Talk:Chapter_Extension

No, this wasn't me - but nice to see that others are interested too ... ;)

> 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?

We just get this feature request and are implementing this ATM for MP4 
and MP3 audio - and thought it would be nice to have in Vorbis too ...
In MP4 you have a separate track, in MP3 (ID3) this is directly attached 
to the chapters [1].

Podcast authoring software, like Hindeburg (see [2] how they create 
chapters) or I thing also Garageband, allows you to set a link and a 
picture for a chapter, and clients also display them (e.g. players on 
the "i-devices" or the popular instacast [3]).

> 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, that would be the other possibility.

However, do you know if (hardware) player have problems with ogg audio 
files with kate tracks?
Because it would be quite trivial to add them in the VorbisComment 
header ...


>> 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.

Note: I am speaking about audio only files (although that might be 
useful for videos as well).
In enhanced podcasts these images are displayed when you play the file.

> 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?

Yes, I also thought about this way ...
However, AFAIK there are problem with some hardware players if the 
vorbiscomment header gets too big?
And if you have multiple images, the header will be very big ...

> 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.

OK, thanks. I thought images are also possible with OggKate as noted here:
http://wiki.xiph.org/OggKate#Images


Thanks for the answers!
LG
Georg


[1]: http://www.id3.org/id3v2-chapters-1.0
[2]: see this video on how to create chapters with links and images with 
hindeburg: 
http://www.youtube.com/watch?v=Ago1_7aLYQY&feature=plcp&context=C4f45b8eVDvjVQa1PpcFP7RTwouNwgPPcMIyFDSz86-Fh1LfinAw8%3D
[3]: http://vemedio.com/products/instacast

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