RE: Proposal from HbbTV

Dear Bob, Alexander,

I'd like to comment on one of the points in the email exchange below, the mapping of id to PID.

Please see in-line. Other items are snipped as Alexander is far more qualified to comment than I am.

Jon
________________________________________
From: Bob Lund [B.Lund@CableLabs.com]
Sent: 29 September 2014 23:46
To: Alexander Adolf
Cc: Jon Piesing; Silvia Pfeiffer; W3C Inband Tracks Reflector; Nigel Megitt
Subject: Re: Proposal from HbbTV

<snip>

>>> For @id, why doesnąt the use of PID work.
>
>>PID can't work in Europe as we do a lot of forwarding of broadcast
>>streams and service aggregation. A service on a cable trunk for instance
>>may come from a terrestrial feed, which in turn is sourced from a
>>satellite feed, and the cable operator is mixing is some more services
>>from another satellite or another cable. The probability that the PID
>>will be changed a couple of times along the way is quite high. For this
>>reason DVB has invented the stream identifier descriptor, bearing a
>>component_tag. Even if the PID changes the tag is retained.

>But why does it matter? The transport stream still requires that PIDs be
>unique. So, each HTML track will have a unique id if PID is used. What
>else does the track.id need to convey to the Web application?

For DVB systems, the spec might as well just require that the id be a unique identifier arbitrarily assigned by the UA rather than requiring that identifier to be the PID.

>
>> And, why canąt the pid be a decimal representation as in the case of
>>ATSC?
>> [...]
>
>Because we needed an easy way of telling whether the component_tag or the
>PID is given.
>

In a DVB system, component_tag is useful to expose to HTML but it's unfortunately not mandatory to provide.

Jon

Received on Tuesday, 30 September 2014 07:37:25 UTC