AW: Definition of ma:fragments and ma:namedFragments

Dear Raphaël,

actually my comment was really more concerned with the definition of the ma elements than with all the guts of the fragment definitions ...

> I'm not sure I understand the distinction you make. I don't understand
> either why there are two properties in the first place? Perhaps an
> example of how the property will be used would help ...

The rationale behind the two elements is the following: ma:fragments is meant to contain a list of fragments (of any type) of that media resource, these could be chapters, scenes, clips a user likes, etc. The API can then be used to query annotations of the fragment, so ma:fragment links different granularities of annotations. These fragments could also be named fragments, with all the issues you have pointed out.

The reason to have ma:namedFragments is different. It addresses the discovery problem that you mentioned, i.e. to determine what the valid range values for each type of fragment identifier is. The ma properties allow to answer this query for temporal, spatial and track fragments by using the appropriate technical properties. For named fragments, ma:namedFragments would return the list of valid fragment labels for the resource.

The issue I raised yesterday was not related to labels from container formats, but to identifiers of fragments in metadata documents that are accessed using the media annotation API. Assume you have an MPEG-7 document, which describes the shot structure of a video. Each VideoSegment can have an ID, so that, given the media resource is http://foo.com/video a shot could be http://foo.com/video#1, which is an identifier for this fragment and a URI, but not a media fragment URI. In this case ma:fragments should contain http://foo.com/video#1, and when requesting the ma:location property of this fragment one would get e.g. http://foo.com/video/video.mpg#t=10,20

I hope this clarifies things a bit.

Best regards,
Werner

> -----Ursprüngliche Nachricht-----
> Von: Raphaël Troncy [mailto:Raphael.Troncy@cwi.nl]
> Gesendet: Donnerstag, 01. Oktober 2009 17:33
> An: Bailer, Werner
> Cc: public-media-annotation@w3.org
> Betreff: Re: Definition of ma:fragments and ma:namedFragments
> 
> Dear Werner, all,
> 
> Let me jump into this discussion :-) I agree that the current
> definitions of ma:fragments and ma:namedFragments are pretty fuzzy.
> 
> Some clarifications: it *might* (see warning) be possible to specify
> within a Media Fragment URI a name referring to a fragment of a video.
> For example, assuming the producer of the video 'foo.flv' has encoded
> and marked up the video with cue points [1]. The video contains
> markers,
> referring to a time interval and noted "love scene". These cue points
> refer to the time offset 42m15s till 46m57s in the flash header.
> A media fragment URI referring to this fragment would be:
> http://www.example.com/foo.flv#id='love%20scene'
> 
> Assuming now that the media server understands this media fragment URI,
> it could serve this range request with just the bytes corresponding to
> this time interval. The UA will play this sequence but display the full
> length duration of the source video so that the user is aware he is
> just
> watching an excerpt of it.
> 
> Warning: this is the ideal scenario, but I first wrote "might" since it
> is unclear at the moment how the "named" dimension will actually work
> in
> the media fragment URI spec. The WG is still working on it.
> 
> > When working on the implementation of our mapping prototype we came
> > across an issue with the definition of the ma:fragments and
> > ma:namedFragments elements. My understanding was (and this is
> > supported by the examples in the table) that both contain lists of
> > identifiers conforming to the media fragment URI specification. I
> > still think that this should be the case for ma:namedFragments, i.e.
> > listing the defined name fragments for a resource.
> 
> The problem of named fragments is that:
>    - you need container formats that deal with named sections or
> chapters (see [2])
>    - you need to know which named sections have been defined in a
> particular video file, i.e. discovery problem
> 
> > However, in some metadata standards it is possible to assign
> > identifiers to fragments (e.g. shots), and during mapping it seems to
> > make sense to keep the identifier of the fragment (which could be any
> > URI), and in addition provide the ma:locator property for the
> > fragment, which would really be a media fragment URI (e.g. the
> > temporal fragment representing the shot).
> 
> Are you sure about that? Do you know which constraint the various
> container formats put on how you can label the fragment? Are you sure
> you can use anyURI? Our reference is currently:
>    - The QTText for .mov files
>    - The MPEG-4 Part 17 for .mp4 and .3gpp files
>    - The MPEG-21 spec
>    - The CMML and ROE format for .ogv files
>    - The cue points spec for .flv files
>    - we need to complete the list for .mkv, .mxf and .asf
> 
> > To summarize: the current specification of the ma:fragments and
> > ma:namedFragments properties is not very precise, it talks about
> > fragment identifiers. I think that we should be clear whether we mean
> > media fragment URI compliant ones or any URI. From the problem above
> > it seems that it should be any URI for ma:fragments (which does of
> > course not exclude media fragment URIs) and media fragment URIs for
> > ma:namedFragments.
> 
> I'm not sure I understand the distinction you make. I don't understand
> either why there are two properties in the first place? Perhaps an
> example of how the property will be used would help ...
> 
>    Raphaël
> 
> [1]
> http://help.adobe.com/en_US/Soundbooth/2.0/WSA5A1DDFB-6BE2-4486-BE0C-
> A10CEEF119ADa.html
> [2]
> http://www.w3.org/2008/WebVideo/Fragments/WD-media-fragments-
> reqs/#fitness-table
> 
> --
> Raphaël Troncy
> EURECOM, Multimedia Communications Department
> 2229, route des Crêtes, 06560 Sophia Antipolis, France.
> e-mail: raphael.troncy@eurecom.fr & raphael.troncy@gmail.com
> Tel: +33 (0)4 - 9300 8242
> Fax: +33 (0)4 - 9000 8200
> Web: http://www.cwi.nl/~troncy/

Received on Thursday, 1 October 2009 16:14:26 UTC