- From: Cyril Concolato <cyril.concolato@telecom-paristech.fr>
- Date: Fri, 27 Jul 2012 12:00:47 +0200
- To: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
- Cc: whatwg@lists.whatwg.org
Hi Silvia, [trimming a bit the text to keep the email short] Le 7/27/2012 12:35 AM, Silvia Pfeiffer a écrit : > > There is the SVG viewbox and there is the video viewbox. It is not > immediately clear how they relate to each other. What I meant was: how > to position the SVG viewbox within the boundaries of the video > viewbox. It could fully cover it, but it may not need to. For example > in your example with the clock, it could be positioned by coordinates > of the video, e.g. left: 70%, top:30% or something like it. Then the > SVG can be much smaller and it is possible to overlay other elements, > too. I understand. What I'm saying is: when SVG is used as track, make it simple, both viewboxes are the same. > You could, however, put SVG in WebVTT e.g. to provide overlay graphics > that are non-moving or are in a loop for a certain duration of the > video. E.g. an animated character (like your Rhino) could be rendered > in a loop on top of a video for the first 3 minutes of the video. Agreed, why not. > > I don't want to take this discussion off track, but it is news to me > that TTML can express frame-based animations. > I indeed wouldn't mingle WebVTT and TTML layering since they satisfy > the same use cases. I've seen examples like that, used to carry DVB subtitles, urgh! > How does the browser support constructing SVG progressively right now? > If there is a SVG-internal solution, that should be used. In this > case, @mediagroup synchronization would again make the most sense. Or > you just do everything in SVG. Browsers construct SVG progressively right now as they do for HTML. The parser parses the data as it receives it. @mediagroup is indeed a solution but the track has other advantages. Controlling the time when the data is received for instance with inband stored track is one. > No, not really. What I meant was to draw the blue handle on top of the > video not through cues, but directly in the browser. Then, the WebVTT > file only delivers the according position changes for that particular > time and all you need to do in JavaScript is to change the handle > position in the SVG. That makes the WebVTT slimmer and not contain any > SVG at all. Right, but that again requires JS, and hence incurs some processing penalty. And also, this requires a dedicated authoring while using an SVG track, you could just use any existing tool. >> The basic Track interface would be almost the same as the VideoTrack or >> AudioTrack. The GraphicsDocumentTrack interface would be used for tracks >> which have an underlying document (TTML, SVG, SMIL?, HTML?...) with a visual >> representation and not necessarily based on cues. For these documents, you >> are not interested in cues or cue changes (and it might not make sense to >> define cues). For these, you're only interested in: >> - the dispatch of the track content to the parser being done automatically >> by the browser (no need to use a JS DOMParser); >> - the rendering of the underlying document being synchronized (natively) by >> the browser, i.e. the timeline of the underlying document should be locked >> with the timeline of the video (or audio). No need to monitor cue changes to >> render the right SVG. >> You could discriminate between a TextTrack and a GraphicsDocumentTrack by a >> mime type or the inBandMetadataTrackDispatchType (not sure...). When the >> track carries SVG, the trackDocument object could be an SVGDocument. This >> would allow for controlling the SVG as if it was embedded in the HTML but >> for the synchronization done by the browser. What do you think? > Why does it have to be a track at all? Video and audio can be > synchronized to each other without one needing to be a track of the > other. To use @mediagroup, you might need to consider what an SVG > graphic has to provide for the MediaController [1]. There is no > need to consider cues and tracks - we seem to agree on that. :-) We seem to agree on many things but not all ;) We agree that there are use cases for SVG graphics synchronize and overlayed on top of a video and that @mediagroup is a solution. The track mechanism (without cue) has several advantages: - synchronization equivalent to the @mediagroup solution - reuse of SVG native behavior (progressive loading) equivalent to the @mediagroup solution - selectability of the track using the default UI controls, just like with subtitles, without needing specific controls. - rendering on top of the video (just like subtitles) without interfering with the UI controls. - unified handling of out-of-band and in-band SVG tracks. Note, that this would be perfectly applicable to HTML/CSS animations on top of a video. It is just enlarging the scope of tracks, currently restricted (except for video and audio) to cue-based formats and text only. Regards, Cyril -- Cyril Concolato Maître de Conférences/Associate Professor Groupe Multimedia/Multimedia Group Telecom ParisTech 46 rue Barrault 75 013 Paris, France http://concolato.wp.mines-telecom.fr/
Received on Friday, 27 July 2012 10:01:25 UTC