[mythtv-users] HDTV and Myth Chan Scan

[R. G. Newbury]

Michael Haan wrote:
> On 2/17/06, *R. G. Newbury* <newbury at mandamus.org 
> <mailto:newbury at mandamus.org>> wrote:
>
>       Take a look at the channel table. There must be an mplexid entry
>     for
>     channel 213 (as well as a serviceid). You will need to do:
>
>     update channnel set mplexid = 'x', serviceid='y' where channum='213';
>
>     Geoff
>
>
> Yeah, I'm just curious why the scan didn't do that.  From the table 
> above, how do I know which mplexid to set?  And where do I find the 
> service ids?
Because the scan doesn't. Although it will now import a channel.conf 
file and it may massage that file sufficiently to do that.

I'm not going to repeat things at great length yet again. Go to gossamer 
threads and search on a subject title "pcHDTV Sweet..."

This thread is specifically for  North American HTDV on cable using 
QAM_256.  It may help with other setups however.
 
You will need some programs referred to in that thread:  atscscan and 
azap. and mplayer for testing.

atscscan will tune all the standard frequencies and read the stream for 
video id, audio id and program id information. It may or may not be able 
to parse the channel name and it will not generally find out the cable 
channel number.

You will get a list of usable outputs, which will make up your 
channels.conf. These are "channels".. and many are in fact music (audio 
only) feeds. With my cableco I get numbers up to about 800 . Most of the 
audio streams are usable btw.
You can tune each channel with azap in one console and capture the 
stream with 'cat /dev/dvb/adapter0/dvr0 > test.mpg' in another console 
then play it back with 'mplayer test.mpg'.
Someone posted a script which will do the things on the above line 
automagically and find the unencrypted streams.
You can also tune with azap in one console and use mplayer -vid x -aid y 
/dev/dvb/adapter0/dvr0 where x and y are the video and audio ids found 
with the scan.

Each frequency carries multiple streams. Each frequency is uniquely 
differentiated by its mplexid in the dtv_multiplex table (together with 
the modulation and other simliar details which all of the streams have 
for that frequency.

The channel table then needs entries for the mplexid, to know the 
freqeuency and the serviceid to know which stream to capture for channel 
213. Along the way, the system also knows that this channel is in the 
sourceid=x group and therefor that it can use the tuners which are 
matched to that sourceid.

The particular problem is that, at least around here, cableco's do not 
have to send channel name information in the stream. They (also) 
determine the 'channel number' which is just a convenient and unique 
marker for the channel. It does not have any relevance to the tuning 
problem. And, the cableco can and does change the program id (or 
serviceid) for channel streams..

All of which make it damn difficult to scan for and extract the proper data.

Geoff




-- 
       R. Geoffrey Newbury			
     Barrister and Solicitor
 Suite 106, 150 Lakeshore Road West
    Mississauga, Ontario, L5H 3R2

  905-271-9600  Fax 905-271-1638
       newbury at mandamus.org