Re: Proposal from HbbTV



On 9/30/14, 1:36 AM, "Jon Piesing" <Jon.Piesing@tpvision.com> wrote:

>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 doesn©öt 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.

So the unique identifier assigned by the UA could be the PID, right? It
would best for interoperability if the the UA set the MPEG-2 TS track id
the same way in all cases.

>
>>
>>> And, why can©öt 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.

How is it useful if it¡¯s not guaranteed to be present?

>
>Jon

Received on Tuesday, 30 September 2014 16:14:23 UTC