- From: Jack Jansen <Jack.Jansen@cwi.nl>
- Date: Thu, 18 Nov 2004 22:54:55 +0100
- To: Cyril Concolato <cyril.concolato@enst.fr>
- Cc: www-tag@w3.org, symm@w3.org, www-international@w3.org, SVG WG <w3c-svg-wg@w3.org>
On 17-nov-04, at 10:15, Cyril Concolato wrote: > "The video element specifies a video file which is to be rendered to > provide synchronized video. The usual SMIL animation features are used > to start and stop the video at the appropriate times. An xlink:href is > used to link to the video content. It is assumed that the video content > also includes an audio stream, since this is the usual way that video > content is produced, and thus the audio is controlled by the video > element's media attributes." The reason for having the <video> tag control both audio and video is that long ago (I think as far back as SMIL 1.0 standardisation) we recognized that having <video> play only the video part and a parallel <audio> to play the audio part would either result in losing lip-sync, or place a heavy burden on implementations to detect this parallelism. In case of RTSP streams this would become an even bigger problem. And then there's the added problem that <video> doesn't really have any different semantics than <audio>, the only difference is documentary (the mimetype of the media item governs what it is). We toyed with various ideas along the lines of having tags that merely define a stream and then use some scheme to address substreams from within this stream, but it quickly turned out that it would be a lot of work to come up with an addressing scheme that would be sufficiently general, so we postponed it. In the mean time, implementations can use the <param> mechanism (or even url?parameter) to provide this functionality. But note that this is only the historical explanation: I fully agree that some way to have more control over which bits of multiplexed streams are rendered is needed. -- 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 Thursday, 18 November 2004 21:54:57 UTC