[mythtv-users] How does myth use info in channel table to tune QAM channels?

[Michael Thome]

Which database fields does myth use to tune QAM channels?  How do these 
rules interact with zap2it lineups?

Background:  I've got an HDHR connected to cable to get the unencrypted 
QAM256 channels.  I can scan for 'em, watch 'em, etc, but:
1. Most of the program streams dont have PID/ATSC information associated 
with them, and those that do don't quite match zap2it's keys.
2. none of the streams are in the same place as OTA.
3. The set of unencrypted channels contains all the OTA channels plus a 
few of the (local) cable channels - the cable company's published lineup 
does *not* include all the OTA channels, so none of the zap2it lineups 
covers everything.

Example: here is an extract of what the channel table looks like after a 
successful scan:

mysql> SELECT 
chanid,channum,freqid,callsign,xmltvid,tvformat,mplexid,serviceid,atsc_major_chan,atsc_minor_chan 
FROM `channel` WHERE `sourceid` = '5';
| chanid | channum | freqid | callsign     | xmltvid | tvformat | 
mplexid | serviceid | atsc_major_chan | atsc_minor_chan |
|   5041 | 4.1     | 87     | WBZ-DT       |         | ATSC     |     
132 |         2 |               4 |               1 |
|   5740 | 74#0    | 74     | UNKNOWN74#0  |         | Default  |     
120 |        65 |               0 |               0 |

for 5041, channum is reasonable, but we couldn't match zap2it because 
87.2 isn't 4.1 and WBZ-DT isn't WBZDT.  I assume that I can insert the 
right xmltvid (20431) and I'll get lineups, but is it safe to change the 
callsign to match (or is it totally ignored by tuning and schedule)?

for 5740, by watching the stream I can see it is WENH (xmlid 11418).  I 
assume I can add the xmltvid and scheduling will work, but I'd also like 
to fix the channum for the on-screen schedule (74#0 isn't mnemonic) - 
can I change channum to "11"?  callsign to "WENH"? What is mplexid? Why 
is tvformat entered as "Default" and not "ATSC"?  Shouldn't it be ATSC 
with atsc_major/minor_chan set to something useful?  As an aside, how'd 
we get from 74.65 (what an hdhomerun_config scan reports) to 74#0?

Obviously, I actually have tried fooling around with these fields - I 
usually end up with broken channels, though:  for instance in the second 
case above, changing channum=11, callsign=WENH, xmltvid=11418 leads to 
nice looking schedule information attached to an un-tunable channel: I 
would have thought that freqid=74, serviceid=65 and sourceid=an hdhr 
source was plenty to tune successfully.

Thanks!