- From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
- Date: Fri, 8 Nov 2013 10:37:29 +1100
- To: Bob Lund <B.Lund@cablelabs.com>
- Cc: "public-inbandtracks@w3.org" <public-inbandtracks@w3.org>
On Fri, Nov 8, 2013 at 3:03 AM, Bob Lund <B.Lund@cablelabs.com> wrote: > > Video, audio and text tracks all need an attribute, track id, label or > whatever, so that the track can be correlated with the that tracks > metadata, as described below. That's already part of the HTML spec, see http://www.w3.org/html/wg/drafts/html/master/embedded-content-0.html#audiotrack . So this is not something that we need to develop, but something we can make use of. > MPEG-2 TS Descriptive video service in North America is a secondary audio > track with the main dialogue and video descriptions premixed. There is no > @kind value to denote this, so the only way the Web app can identify such > a track is by examining the metadata descriptor. Yes, there is. Audio tracks have @kind values, too, see: http://www.w3.org/html/wg/drafts/html/master/embedded-content-0.html#dom-audiotrack-kind . I assume you want to look at how to identify such tracks in MPEG-2 and map that to the existing HTML spec @kind values, seeing as the list in the above link does not describe how to do this for MPEG-2 or MP4. That makes sense. > So, the UA recognizes the > track as audio (stream type will denote type of audio). The UA should also set the @kind. We can make some suggestions for how to do so. > Web app examines > the track metadata to determine type of audio and then parses remaining > metadata to determine if the audio is combined main dialogue + video > description. No, the Web app just needs to investigate the @kind value. >>> For more deterministic handling of inband tracks, the UA could be >>>required >>> to: >>> >>> * Expose all in-band tracks, in some form. >> >>If they are audio or video tracks that the browser does not recognize >>as such, it will be pretty useless to expose them, since a JS app is >>likely not in a better place to decode them than the browser. > > Maybe, but then this should be stated. OK, that's a one-liner to be added to the HTML spec. Worth a bug, I guess. >>> * Provide data so that the Web application can correlate the metadata >>>data >>> with the appropriate Track object. >> >>What does that mean? > > If JS receives metadata associated with inband tracks, as proposed above, > then it needs to be able to relate this metadata to tracks in the > tracklist objects. In [1], this is done by assigning the elementary stream > packet ID (PID) to the track.label. JS has the PID as part of the metadata > so it can make the association. Equivalent IDs exist in other media > container formats. OK. Cheers, Silvia.
Received on Thursday, 7 November 2013 23:38:19 UTC