- From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
- Date: Fri, 1 Apr 2011 09:41:52 +1100
- To: Eric Carlson <eric.carlson@apple.com>
- Cc: Ian Hickson <ian@hixie.ch>, Mark Watson <watsonm@netflix.com>, "public-html-a11y@w3.org" <public-html-a11y@w3.org>
On Fri, Apr 1, 2011 at 1:49 AM, Eric Carlson <eric.carlson@apple.com> wrote: > > On Mar 30, 2011, at 9:22 PM, Silvia Pfeiffer wrote: > >> But I am told, UAs render them simply over each other >> at the top left corner. In any case, there will be a default rendering >> IIUC. >> > This is not quite right. Every visual track in MPEG-4 and QuickTime containers, at least, has a display matrix that determines where it is rendered. The movie's display box is the union of all visual track display boxes, eg. the size and position of a visual track affects the size of its movie. > > It is certainly *possible* to render an in-band track in the top left corner, and that may be the default in some media authoring software, but it is not a requirement. Thanks for the clarification. It confirms though that multiple in-band video tracks are indeed rendered by default into the existing video viewport unless they are somehow turned off. I now wonder: is there actually a means to turn them off and just use them in a separate audio or video element with a fragment identifier? In multitrack in-band resources, are the multiple media tracks typically all activated by default or how is the decision made whether to render them? Silvia.
Received on Thursday, 31 March 2011 22:42:45 UTC