[mythtv] Re: Ticket #109: DVB/ATSC patch to allow configuring channels via channels.conf

[Christiaan Lutzer]

If you consider a MPTS, you only need to specify the program number
(PN) to tune to a specific program in the stream.  A good example is
Comcast Cable.  They are moving to a more dynamic architecture whereby
set tops tune to digital program by frequency and program number. 
Assuming a MPTS in the clear, that's all the information you need
(assuming QAM 256, etc.) to tune to a given program.

Once you know the PN, you can examine the PMT to glean the audio and
video pids (as well as any other pids such as data, etc.) that belong
to the program.  I think within the context of MythTV, the program
number is refered to as the service ID.  I work for a company that
builds digital media solutions (VOD, Network PVR, Ad-insertion), and
we always refer to it as the program number (the MPEG-2 TS standard
refers to it as program number as well).  That is the only additional
field that I added to the ATSC channels.conf case.  It works great.

It would be redundant, and incorrect to specify the audio/video pids,
because technically (as far as I know) they are arbitrary with respect
to the program number.  It's really up to the MSO and their TS gear. 
A parallel example would be in the use of DSM-CC to control VOD
sessions, upon a session setup response, the set top is given a
frequency and program number to tune to (in a typical HFC plant). 
Given that program number, the PAT and PMT are inspected for
audio/video pids.

You'll notice that I only added the service ID parsing for the ATSC
case.  The original author must have been thinking along the same
lines, but perhaps he assumed a service ID, as opposed to a specified
one.

Anyway, I hope that made sense.

Christiaan.

On 7/15/05, MythTV <mythtv at cvs.mythtv.org> wrote:
> #109: DVB/ATSC patch to allow configuring channels via channels.conf
> ---------------------+------------------------------------------------------
>        Id:  109      |      Status:  assigned
> Component:  mythtv   |    Modified:  Fri Jul 15 15:08:14 2005
>  Severity:  medium   |   Milestone:  0.19
>  Priority:  minor    |     Version:  head
>     Owner:  danielk  |    Reporter:  mythtv.lutzer at gmail.com
> ---------------------+------------------------------------------------------
> Changes (by danielk):
> 
>   * status:  new => assigned
>   * owner:  ijr => danielk
> 
> Comment:
> 
>  I believe the format should be
> 
>  name,frequency,modulation,atsc channel,[video pid, audio pid 1, audio pid
>  2, ...]
> 
>  With the things in brackets being optional and atsc channel
>  reported as NULL if a proper VCT is missing.
> 
>  I'll accept this ticket, but it might be a little time before
>  I apply it or something like this since I'm working on scanning
>  right now in my check signal patch.
> 
> --
> Ticket URL: <http://cvs.mythtv.org/trac/ticket/109>
> MythTV <http://www.mythtv.org/>
> MythTV