Re: Proposal from HbbTV

Dear Bob,

On 2014-10-13, at 23:40 , Bob Lund <B.Lund@CableLabs.com> wrote:

>> [...]
>> - In 3.3 for @id you use program_number zero to detect a DVB stream. That
>> program number is however assigned by MPEG (not DVB) for the network
>> information table. Unfortunately DVB is not the only standard to use this
>> mechanism; ISDB uses it too. Therefore, if program zero is present it may
>> be a DVB or an ISDB stream.
> 
> Doesn¡¯t the original_network_id (or some other field) carried in the
> program 0 identify whether it is DVB or something else?.

The original_network_id is buried in data structures in MPEG tables. So you would need to make a reasonable guess about which format the table payload has, before being able to parse out the original_network_id. Catch 22.

> [...]
> With that said, I had asked in a previous email whether it is mandatory
> for a DVB TS to carry something that identifies is as DVB, for the example
> the transport_stream_descriptor in PID 0x02.

As I had responded in one of my previous emails, there isn't.

> Your original contribution in
> this regard [1] described several things a UA might be able to look at to
> distinguish DVB but there didn¡¯t seem to be anything the UA could count on
> being there. If there was something the UA could count on to identify DVB
> then this could be referenced.
> [...]


Unfortunately there is nothing that the UA can count on.

With that said, it doesn't mean that it couldn't relatively easily be put there. My suggestion would be for W3C to be in touch with ATSC, DVB, and ISDB and propose to them making the transmission of the TSDT mandatory in their specifications, and put a transport_stream_descriptor in it to allow receivers to unambiguously identify the system type. I shall be happy to help you crafting the message.


Cheers,

  --alexander

Received on Tuesday, 14 October 2014 09:29:14 UTC