Re: Proposal from HbbTV

On 10/14/14, 3:28 AM, "Alexander Adolf"
<alexander.adolf@condition-alpha.com> wrote:

>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.
>> 
>> Doesnšt 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.

Why is guessing involved? Each section/table starts with a table ID field
which identifies the type of table. It should be deterministic to find the
original_network_id: the PAT identifies the PID carrying the NIT which,
according to DVB-SI, carries the network information section with the
original_network_id for each TS.

>
>> [...]
>> 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.

Sorry, missed that.

>
>> Your original contribution in
>> this regard [1] described several things a UA might be able to look at
>>to
>> distinguish DVB but there didnšt 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.

How about HbbTV making a recommendation to DVB, citing the Web use cases
wešve been discussing. I would be happy to work with you on that.

>
>
>Cheers,
>
>  --alexander
>

Received on Tuesday, 14 October 2014 15:14:04 UTC