- From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
- Date: Fri, 1 May 2009 11:42:54 +1000
On Fri, May 1, 2009 at 2:25 AM, David Singer <singer at apple.com> wrote: > At 23:15 ?+1000 30/04/09, Silvia Pfeiffer wrote: >> >> ?> On Thu, 30 Apr 2009, Silvia Pfeiffer wrote: >>>> >>>> ?> On Wed, 8 Apr 2009, Silvia Pfeiffer wrote: >>>> ?>> >>>> ?>> Note that in the Media Fragment working group even the specification >>>> ?>> of http://www.example.com/t.mov#time="10s-20s" may mean that only >>>> the >>>> ?>> requested 10s clip is delivered, especially if all the involved >>>> ?>> instances in the exchange understand media fragment URIs. >>>> ?> >>>> ?> That doesn't seem possible since fragments aren't sent to the server. >>>> >>>> ?The current WD of the Media Fragments WG >>>> ?http://www.w3.org/2008/WebVideo/Fragments/WD-media-fragments-reqs/ >>>> ?specifies that a URL that looks like this >>>> ?http://www.w3.org/2008/WebVideo/Fragments/media/fragf2f.mp4#t=12,21 >>>> ?is to be resolved on the server through the following basic process: >>>> >>>> ?1. UA chops off the fragment and turns it into a HTTP GET request with >>>> ?a newly introduced time range header >>>> ?e.g. >>>> ?GET /2008/WebVideo/Fragments/media/fragf2f.mp4 HTTP/1.1 >>>> ?Host: www.w3.org >>>> ?Accept: video/* >>>> ?Range: seconds=12-21 >>>> >>>> ?2. The server slices the multimedia resource by mapping the seconds to >>>> ?bytes and extracting a playable resource (potentially fixing container >>>> ?headers). The server will then reply with the closest inclusive range >>>> ?in a 206 HTTP response: >>>> ?e.g. >>>> ?HTTP/1.1 206 Partial Content >>>> ?Accept-Ranges: bytes, seconds >>>> ?Content-Length: 3571437 >>>> ?Content-Type: video/mp4 >>>> ?Content-Range: seconds 11.85-21.16 >>> >>> ?That seems quite reasonable, assuming the UA is allowed to seek to other >>> ?parts of the video also. >>> >>> >>>> ?> On Thu, 9 Apr 2009, Jonas Sicking wrote: >>>> ?>> >>>> ?>> If we look at how fragment identifiers work in web pages today, a >>>> ?>> link such as >>>> ?>> >>>> ?>> http://example.com/page.html#target >>>> ?>> >>>> ?>> this displays the 'target' part of the page, but lets the user >>>> scroll >>>> ?>> to anywhere in the resource. This feels to me like it maps fairly >>>> ?>> well to >>>> ?>> >>>> ?>> http://example.com/video.ogg#t=5s >>>> ?>> >>>> ?>> displaying the selected frame, but displaying a timeline for the >>>> full >>>> ?>> video and allowing the user to directly go to any position. >>>> ?> >>>> ?> Agreed. This is how the spec works now. >>>> >>>> ?This is also how we did it with Ogg and temporal URIs, but this is not >>>> ?the way in which the standard for media fragment URIs will work. >>> >>> ?It sounds like it is. I don't understand the difference. >> >> Because media fragment URIs will not deliver the full resource like a >> HTML page does, but will instead only provide the segment that is >> specified with the temporal region. >> http://example.com/video.ogg#t=5s ?only retrieves the video from 5s to >> the end, not from start to end. >> >> So you cannot scroll to the beginning of the video without another >> retrieval action: > > which is fine. ?I don't see the problem; ?given a fragment we > a) focus the user's attention on that fragment > b) attempt to optimize network traffic to display that fragment as quickly > as possible > > Neither of these stop > c) the user from casting his attention elsewhere > d) more network transactions being done to support this re c): It depends on how the UA displays it. If the UA displays the 5s offset as the beginning of the video, then the user cannot easily jump to 0s offset. I thought this was the whole purpose of the discussion: whether we should encourage UAs to display just the addressed segment in the timeline (which makes sense for a 5sec extract from a 2 hour video) or whether we encourage UAs to display the timeline of the full resource only. I only tried to clarify the differences for the UA and what the user gets, supporting an earlier suggestion that UAs may want to have a means for switching between full timeline and segment timeline display. Ultimately, it's a UA problem and not a HTML5 problem. Cheers, Silvia.
Received on Thursday, 30 April 2009 18:42:54 UTC