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Manually configuring QAM channels not found in scan
PostPosted: Wed Jul 13, 2005 12:03 am Reply with quote

When I do a QAM channel scan, most of the HD stations on my Comcast cable are found. Most of them are retransmissions of the ATSC broadcasts from my local channels. They are rebroadcast without modification, with the PSIP data and all, and MythTV finds them, with

But, a couple of them, like ESPN-HD don't have the PSIP data and are not seen by MythTV. I know it is broadcast in the clear, because I can watch it with my MyHD card in Windows.

Is there some way for me to manually add the channel into MythTV? It is on a subchannel of a QAM station, 116-2. So, I'm not sure how to add the subchannel info.

Has anyone else run into this?
PostPosted: Thu Jul 14, 2005 2:39 pm Reply with quote
Joined: 09 Apr 2004
Posts: 15

Okay, after struggling with this for a couple days, I'll try to post some info on it here for the next guy..

- Make sure you set the initial channel in the mythtv-setup (where you connect the DVB device to the guide data source). Otherwise, MythTV just displays a blank screen if it can't tune the initial channel.

- Do a channel scan in mythtv-setup. I had to do a full ATSC scan before a QAM scan, or it wouldn't find any channels. I'm not sure if that's the same for all cards. It should find channels with PSIP data at this point, then you'll only need to make sure they are matched up with the XMLTV ID's for guide data.

- For channels not found in the channel scan, you will need to manually add their config data (which is unfortunately in MySQL, rather than a simple config file).

I used MythWeb to view/edit the channel data. I had to hack a couple of the PHP files to view/edit/save the appropriate data. The missing attributes were: mplexid, serviceid, and atscsrcid.

As far as I can tell, the mplexid refers to the channel that was found in the mythtv channel scan. This is stored in the "dtv_multiplex" section of the database. You just need to find the frequency of the QAM channel you are trying to set with in the "dtv_multiplex" section. The mplexid is the first attribute on that record. (A listing of all QAM channel frequencies can be found with the azap tool).
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Manually configuring QAM channels not found in scan
PostPosted: Fri Jul 15, 2005 8:48 am Reply with quote
Joined: 28 Dec 2004
Posts: 12

Comcast is apparently not providing data in their QAM channels that the FCC requires. Take a look at this message for some more details. If you can, please call your local Comcast customer service number and complain to them that they're in violation of section 76.640 of FCC regulations that pertain to digial cable broadcast systems. The particular details that Comcast is in violation of is the providing of PSIP (Program and System Information Protocol) data in their QAM streams. Hopefully they'll finally fix this if enough people start complaining about it. Oh yeah, and according to the FCC regulations they were supposed to start providing this information in July 2004 so they really have no excuse for not providing it.

In the meantime, what you'll need to do is modify values in your channel table in mysql. if you've run through a channel scan then you should find entries in both the channel and the dtv_multiplex tables. You'll notice that in the channel table the mplexid & serviceid fields are all NULL and the freqid field probably has the same value as the channum field. These are all wrong.

The freqid field needs to contain the QAM frequency (a number like 591000000) and the mplexid field needs to point to the appropriate entry in the dtv_multiplex table. For example, here in the Boston area where I am I used the dvb-apps (azap, dvbscan, etc.) to determine that channel 805 uses the frequency 591000000. This frequency is listed in my dtv_multiplex table under mplexid 11. Since QAM allows multiple channels per frequency you also need to determine the audio/video pid's (apid/vpid from dvbscan). Channel 805 is the first apid/vpid pair on this frequency, so the serviceid will be 1 (if 805 was the second set of pid's serviceid would be 2, and so on). So, on my system:

update channel set freqid=591000000 where channum=805;
update channel set mplexid=11 where channum=805;
update channel set serviceid=1 where channum=805;

Go through this hassle with all your channels then restart mythbackend and you should be all set. (And thank Comcast for making it such a pain in the *ss! Twisted Evil)

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PostPosted: Thu Aug 04, 2005 6:54 pm Reply with quote
Joined: 04 Aug 2005
Posts: 4

I too am having trouble manually configuring QAM channels that Myth missed when it did it's scan. I'm trying to add Discovery HD Theater which I can capture just fine via azap etc, but no such luck in Myth. I've added a new channel manually in the mysql channel db, and mapped it to the mplexid from dtv_multiplex, and I am pretty sure I have the correct sourceid (which is the pid pair that's in the stream), but it gives an error saying the channel is off air.

Here's what I get for the stream running dvbscan -c -v -v:
PMT 0x0022 for service 0x0004
OTHER : PID 0x0880 TYPE 0x80
AUDIO : PID 0x0881
PMT 0x0020 for service 0x0003
VIDEO : PID 0x0800
AUDIO : PID 0x0801
PMT 0x0021 for service 0x0001
VIDEO : PID 0x0840
AUDIO : PID 0x0841

The pid pair that is actually the DHD channel is the first one listed, 880 and 881, service 0x0004, but when I put "4" for the serviceid in the channel db, I get the following error from the backend:

2005-08-04 18:37:45.110 DVB#0 DVB signal c624 | snr f7e3 | ber 0 | unc 0
2005-08-04 18:37:46.414 DVB#0 DVB signal 394 | snr fdb5 | ber 0 | unc 0
2005-08-04 18:37:46.418 DVB#0 Status: LOCK.
2005-08-04 18:37:46.420 DVB#0 Multiplex Locked
2005-08-04 18:37:47.200 DVB#0 Successfully tuned to channel 822.
2005-08-04 18:37:47.203 DVB#0 ERROR - Channel #822 is off air.

One interesting thing to note is that service 3 on that stream is actually the E! channel, while service 1 is unusable. I'm wondering if it may have something to do with the fact that the type is "OTHER" ? It's frustrating because I can capture it just fine outside of myth!
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PostPosted: Sat Aug 06, 2005 8:06 pm Reply with quote
Joined: 04 Aug 2005
Posts: 4

It turns out my problem with manually configuring QAM channels is fixed in the latest cvs..It was indeed what I thought.
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PostPosted: Mon Oct 24, 2005 2:22 pm Reply with quote
Joined: 01 Oct 2005
Posts: 28

your lucky, I only get the OTA stations and a couple random other non-HD digital cable channels (GSN anyone?) over my line. I also notice that through my cable box all the other channels have 5C enabled, so apparently my local Comcast wants to make a killing off renting people cable boxes....

Debian64 via Kanotix, Athlon64 3200+, kernel 2.6.13, HD-3000
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Manually configuring QAM channels not found in scan
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