- From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
- Date: Wed, 24 Sep 2008 20:38:24 +1000
- To: "Yves Lafon" <ylafon@w3.org>
- Cc: "Raphaël Troncy" <Raphael.Troncy@cwi.nl>, "Media Fragment" <public-media-fragment@w3.org>
On Wed, Sep 24, 2008 at 7:43 PM, Yves Lafon <ylafon@w3.org> wrote: > On Wed, 24 Sep 2008, Silvia Pfeiffer wrote: > >>> Giving a name with a well-defined semantics to an object is always >>> subjective. Assuming I have specified a temporal fragment of a video, and >>> I >>> need to give a name to this fragment: for the machines, both the strings >>> "id-3454645" and "kiss-scene" are equivalent. In both case, the machine >>> will >>> not understand what this fragment is about. Similarly, with only the >>> fragment identifier, the machine will not know that this fragment points >>> to >>> a video encoded in the compression format x, under the resolution y, >>> content >>> which is also available on another media server with a different >>> resolution/encoding, etc. This information is what I consider being part >>> of >>> the semantics of the fragment. The questio again is: does this fall into >>> the >>> scope of the WG? >> >> Again, I do not understand your point. The strings "id-3454645" and >> "kiss-scene" are just simple identifier of a segment and do not >> provide any semantics other than the ones that happen in the human >> mind by reading the name. However, defining a referencing scheme where >> we can use the name to identify a fragment is a different thing and >> has nothing to do with semantics. We can still say: this is a URI to >> the fragment called "id-3454645" or the fragment called "kiss-scene". >> Just like class attributes of HTML elements bear no semantics, neither >> do these. > > I think Raphael's point is: should the fragment be self-descriptive enough a > machine can figure out without external context that it is a video fragment. > (re: [[ for the machines, both the strings "id-3454645" and > "kiss-scene" are equivalent. In both case, the machine > will not understand what this fragment is about ]] ). If we only identify that it is a fragment of a *video*, but not what its semantics are, that comes through the media type of the resource, right? > This is especially critical when you want the machine to retrieve only the > fragment and not the whole resource; as opposed to giving a first class > identification to fragments (ie: giving them the resource status). Do you mean that we need to have semantics to identify what segment of a video we need to retrieve? The way I envisage the fragment extraction to work is as follows: * a URI references, say 5.3sec - 20.4sec of videoA * the server maps 5.3sec-20.4sec to a byte range on videoA on the server * the server composes a valid video file (potentially with new headers etc) from the videoA fragment * the server sends that videoA fragment back to the client and notifies it that it is providing a fragment and not the full video If I have misunderstood you, please explain further. > In the case of fragments, being able to merge the 0-10s fragment to the 10s- > (end) fragment in a local cache is something desirable, but it is difficult > to achieve this if fragments are plain resources (unless you have extra > informations available somewhere about relations between a potentially > infinite set of resources), but I'm digressing... Caches are a different matter to servers. While servers know for a given media type how to map time to byte ranges, a cache may not have such information and should only deal with byte ranges. This is particularly true for Web proxies. In that case, we need a special protocol to deal with this situation. We had a plan with Ogg resources and temporal hyperlinks, which I can explain. It would work within the existing Web proxy specifications, but required some extra HTTP message headers (http://annodex.net/TR/draft-pfeiffer-temporal-fragments-03.html#anchor8). Let's discuss that at some other time. :-) Cheers, Silvia.
Received on Wednesday, 24 September 2008 10:39:00 UTC