Doubts in Optional PMT Descriptor

[thatsmohitag]

Hi,

I am working on Japenese ISDB-T receiver Solution for Mobile Segment.
I have a doubt regarding Optional Descriptors in PMT(Programe Map Table),
One of the ARIB Standard mentions optional Descriptor associated with this SI Table.What does the word optional means,Is it optional for the Broadcaster to send or is it optional for the Receiver to interpret it.

Thanks
Mohit

[neuron2]

Please quote the relevant text from the standard.

In my experience it generally means optional to broadcast.

[thatsmohitag]

ARIB B-10 part 2 Annex K Subclause Explanantion mentions
"Digital Broadcasting Signals were standardized to be capable of providing greatly improved convenience for users,compared to conventional broadcast.In particular,signals providing minimum functions necessary for broadcsting were classified as "mandatory"
and signals provided as "needed by" by broadcasting service providers were classified as "optional". "

In paricular if some of the descriptors were optinal then the receiver can not depend on this informaton as the broadcaster might not transmit it.For example it mentions the AVC Timing and HRD Descriptor which talks about the Time Scale of AVC Video ,which is needed by the Demux to manipulate PTSs.But this descriptor is optional.

[neuron2]

It sounds clear to me. The descriptors are optional for the broadcaster, so the player can use them if they are present but must also be able to work in their absence.

If they are present, the player could still ignore them. That could affect the competitiveness of the player in the marketplace, but the standards specify compliant bitstreams, not decoder behavior (although often a model decoder is described in the standard).

[crypto]

The PMT cannot be optional for multi program muxes. There is no other way to associate pids with programs.

[neuron2]

crypto, please read the thread carefully. We're talking about optional descriptors. Nobody is saying the PMT itself is optional.

[crypto]

I see, thanks for clearing that up.

[thatsmohitag]

It sounds clear to me. The descriptors are optional for the broadcaster, so the player can use them if they are present but must also be able to work in their absence.

If they are present, the player could still ignore them. That could affect the competitiveness of the player in the marketplace, but the standards specify compliant bitstreams, not decoder behavior (although often a model decoder is described in the standard).

Thanks Neuron .
But I have a doubt regarding present of Multiple
Accsess Units in a PES in case of ISDB-T Stream,then How to manipulate and get PTS for each Access unit.Each PES carries only
one PTS.

[neuron2]

The PTS applies to the first unit. For the others you have to interpolate based on the frame rate or audio sample rate. Also, not every PES packet has to carry a PTS, so you may have to interpolate across packets as well.

[thatsmohitag]

Say the PTS of Access Unit(1) is 40000 =x.It is a relative value to a Reference clock of 90khz.
Now PTS is a 33 bit Counter Value.

Say FPS is 15FPS.
1frame==1/15 seconds.

How to convert this (1/15)(66.66msec) into a value which can be added to the PTS value to arrive at next AU's PTS.
Is it like 90000 Clock Ticks(1 Tick =1 Time Period of clock) =1seconds

1sec==90000Ticks
1/15 sec==6000Ticks.

Next AU PTS ==40000(x)+6000 and so on..

Is my above computation correct??

I think the FPS is present in AVC Bitstream,Cant this value vary with each Frame ,If so then I have parse the Bitstream for every Frame.If not suggest some other way??