Re: Still about "id" format

From: Jon Piesing <Jon.Piesing@tpvision.com<mailto:Jon.Piesing@tpvision.com>>
Date: Thursday, November 14, 2013 1:33 AM
To: Brendan Long <B.Long@cablelabs.com<mailto:B.Long@cablelabs.com>>, Giuseppe Pascale <giuseppep@opera.com<mailto:giuseppep@opera.com>>
Cc: "public-inbandtracks@w3.org<mailto:public-inbandtracks@w3.org>" <public-inbandtracks@w3.org<mailto:public-inbandtracks@w3.org>>
Subject: RE: Still about "id" format
Resent-From: <public-inbandtracks@w3.org<mailto:public-inbandtracks@w3.org>>
Resent-Date: Thursday, November 14, 2013 1:34 AM

If a content provider has content with >1 track of the same type where these cannot be distinguished by standard per-track metadata then having an id that survives passage through the distribution system has value. In DVB markets, PIDs do not have this property.
Indeed the same elementary stream may have different PIDs in different geographical areas and when received by different distribution channels (cable / satellite / terrestrial / multicast IP).

The PID is used by the Web application to correlate a video, audio or text track, created from an MPEG-2 TS media resource, with the PMT data exposed as TextTrackCues. Thus, it is not required that the PID have any end-to-end identity. The PMT data will contain the component_tag, if present, and therefore Web app can access that if needed.

Using the PID as the track.id seems better since the PID is available in all regions. Also, it is consistent with the idea of using the media resource stream ID as the track id.



Jon
________________________________
From: Brendan Long [B.Long@cablelabs.com<mailto:B.Long@cablelabs.com>]
Sent: 13 November 2013 17:15
To: Giuseppe Pascale; Jon Piesing
Cc: public-inbandtracks@w3.org<mailto:public-inbandtracks@w3.org>
Subject: RE: Still about "id" format


- what is the use case we are trying to address by exposing these info via the track ID attribute? Is the only think we care is to have something that unique locally to the application (in that case it may not matter much if the PID changes along the broadcast value chain as far as each track as a unique PID at the end) or are we trying to convey some other type of information?

One case is the media fragments, where it would probably be useful if the ids were controllable (like Matroska TrackUIDs and Ogg Skeleton Names are), or at least stay the same after transcoding. I assume that would make authoring easier.

The other is finding metadata, where it probably doesn't matter if the ids change, just that they are consistent within a single file.