[ID3 Dev] ID3 chapter tags feedback

Chris Newell chris.newell at rd.bbc.co.uk
Mon Oct 17 02:25:05 PDT 2005

At 00:53 14/10/2005, you wrote:
>Hi – I am new to this list, having just heard about the chapter tags work. I am a researcher at Yahoo Berkeley, working on annotation of time based media, and so we are naturally interested in the work going on with Chapter tagging of MP3 content.
>My colleagues and I went through the docs today, and our first impression is that we like much of what we see. We have a couple of clarifying questions, and some suggestions. I am no expert on MP3 “syntax” and header constraints, so forgive me if I make some silly suggestions that are not in the spirit of MP3.
>My background is with XML formats, and especially SMIL [*]. As such, I was translating in my head from the descriptions I read to how I think about descriptions for timing. I hope this is useful both from the perspective of clarifying the semantics as expressed in your docs, and as an introduction to producing a description of an XML schema that would parallel your work (e.g., as an interchange language for tools producing ID3 Chapter frames).
>In SMIL timing [**], there are two common time containers: “par” (for parallel) and “seq” (for sequence or sequential). Children of par elements have timing relative to the par, but can overlap one another with few constraints. Children of a seq are defined to be a sequence, and are constrained to play one after another, possibly with delays between any two items. While SMIL is defined for synchronization, the basic concepts can be applied to this case as a description of the relationship of the chapters in a CTOC element.  It looks to me like CTOC plus the “Ordered bit” in the flags is more or less equivalent to this – am I right?

Yes. I'm not very familiar with SMIL but this sounds like an identical concept.

>In the spec, the Chapter start time and end time are defined as being relative to the beginning of the file, and yet the CTOC structure implies that there is a hierarchy of chapter elements. I would think that it makes more sense to have the timing reflect the TOC structure. Thus if I have defined a major section of the file as a chapter, I can describe pieces within that section relative to the section begin, rather than from the beginning of the file. This means that start times and byte offsets must be added together to find an absolute offset into the file, but it also means that excerpting a section of the whole file is more straightforward (only the top-level offsets change).
>This would of course require that the CTOC elements also have timing information – does that conflict very much with your current thinking?

Although I can see the advantages during editing I think we should use absolute offsets within ID3 tags as this makes life easier for media players (often low profile devices).

Relative offsets would also break a useful feature of the current proposal - it's possible to refer to a CHAP frame from more than one CTOC. This allows you to provide more than one table of contents for a single file. e.g. for the recording of a rock festival you could provide:
 - a full, temporally ordered table of contents
 - a table providing an index of band names
 - a table listing highlights

>We’ve been playing with some syntax to describe temporal extents in media as part of an annotation framework. We are developing the XML syntax for this now, but I can say that it borrows from SMIL timing syntax (although a good deal more constrained (simpler) than the expressivity of SMIL 2.0 Timing. We are hoping that this would meld well with the ID3 chapter tags work, allowing us a means of encapsulating our semantics in an MP3 file. Have you done anything yet in the area of an XML syntax for the ID3 chapter tags? We’d be happy to contribute to such an effort.

The inspiration for the chapter frame proposal was an open standard for Personal Video Recorders called "TV-Anytime" (http://www.tv-anytime.org/) which I've worked on for a number of years. TV-Anytime has an XML schema which supports chapters (they call it segmentation) and this maps quite well with the binary structures used in the ID3 chapter frame proposal.

Best regards,


Dr J.C. Newell
Digital Media Group, BBC Research & Development
Kingswood Warren, Woodland Way, Tadworth, Surrey 
KT20 6NP  UK
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