Each row in this table describes one tunable channel, where a channel is a unique combination of hardware settings such as frequency, modulation and subchannel id (serviceid) for satellite and digital cable -- if you get CNN from two Video Sources, it will appear twice in this table (though, as long as the callsigns are the same, ScheduledRecordings will be moved from one tuner to another, priorities permitting). The sourceid is used to find a tuner which can tune the channel. The mplexid field is used to point to information in the dtv_multiplex table which will be used to tune the tuner, and the serviceid is used to select a particular digital stream from the tuned feed.
Amended on April 5, 2006 to reflect the present schema (adding new fields)
R. G. Newbury 22.214.171.124 15:56, 5 April 2006 (UTC)
This is a channel record for an atsc digital cable stream, which is nominally on channel 74, but is listed by the cable supplier as channel 406. The mplexid is 110 and the dtv_multiplex table defines the modulation method to be used to decode the stream(in this case QAM_256). The actual stream is denoted by the serviceid of 52.
mysql> select * from channel where mplexid = '110' and chanid = '2743';
| chanid | channum | freqid | sourceid | callsign | name | icon | finetune | videofilters | xmltvid | recpriority | contrast | brightness | colour | hue | tvformat | commfree | visible | outputfilters | useonairguide | mplexid | serviceid | atscsrcid | tmoffset | atsc_major_chan | atsc_minor_chan |
| 2743 | 406 | 74 | 2 | RSP | Sportsnet Pacific | | NULL | | 18801 | 0 | 32768 | 32768 | 32768 | 32768 | atsc | 0 | 1 | | 0 | 110 | 52 | NULL | 0 | 0 | 0 |
Although the channum of 406 is the cable co's. reference (and also used by DataDirect), xmltvid is the unique reference key, as this channel may be given a different number elsewhere on the same cable co. system. The tvformat must be atsc for digital cable or OTA. Note that for cable channels the channel number is a whole number, while OTA uses the 18.2 style.