- From: Jack Jansen <Jack.Jansen@cwi.nl>
- Date: Tue, 25 Nov 2008 23:37:09 +0100
- To: Media Fragment <public-media-fragment@w3.org>
- Message-Id: <36816EB7-6AD4-4E04-A59F-93B03FC8A6AB@cwi.nl>
I have pondered my action item about combining SMIL clipBegin and clipEnd with media fragments, and my conclusion is that the only reasonable course of action is that double clipping occurs. In other words, <video clipBegin="10s" src="http://www.example.com/ myvideo.ogg#t=20s"/> will start playing the video at 30 seconds into the source material. The other option is that the clipBegin of 10 seconds overrides the 20 seconds start time, but that has a serious disadvantage: any program that generates or manipulates SMIL documents will now have to understand both SMIL clipBegin/clipEnd and media fragment URLs. For example, if an XSLT processor was instructed to replace all occurrences of url A with url B it would have to check whether either URL has a media fragment included, and whether any of the occurrences of URL a was on a media tag that uses clipBegin/clipEnd, because in such cases special measures would be needed to make sure the replacement did indeed do what was expected. Double clipping will make life a lot easier, not only for the situation sketched above, but also for SMIL implementations that do not natively understand media fragments but in stead rely on an underlying media access library to provide the data (given a URL). The corollary is that I think this finding is universally true: it applies not only to SMIL but also to other languages, and even to APIs. If a media library (think: ffmpeg, quicktime, directshow, etc) at some point supports URLs with fragments in its "open()" call it should make sure its "seek()" method and related calls will interpret positions relatively to the fragment specified in the URL. Otherwise all applications that use the media library need to be made aware of the existence of media fragments in URLs. -- Jack Jansen, <Jack.Jansen@cwi.nl>, http://www.cwi.nl/~jack If I can't dance I don't want to be part of your revolution -- Emma Goldman
Received on Tuesday, 25 November 2008 22:37:51 UTC