[mythtv-users] multiple channels on same channum

[Michael T. Dean]

On 02/17/2019 01:32 PM, Tim Draper wrote:
> I've been having some issues recently with livetv being very random. It'd never happen for me but seemed when the other half used livetv it'd fail fairly often for her.
> Today it finally happens for me. I get the narrator track for the blind. I exit & re-entering livetv which put me back to the normal audio track so seems to be clearly a channel scan issue.
> I've since removed the multiple channels per channum, so now only 1 channel per channum.
>
> it got me curious - how does mythtv choose which channel to use for those channum's with multiple entries against - random, round-robin, first to respond ?

Channel number is a user-editable field that is only ever used for 2 
purposes: 1) displaying listings information in the guide and 2) telling 
Live TV to switch directly to a particular channel without using the guide.

Therefore, you can, technically, have multiple channels with the same 
channel number and it should have no effect whatsoever on your system. 
The only effect will be on Live TV users who type in that channel 
number, in which case MythTV has no idea which of the channels is being 
requested, so tunes one.  Which one is tuned is whichever one comes up 
first--often related to the data storage in the database, but there's no 
coding to handle "how to pick which one to use" since having the same 
channel number explicitly says the user doesn't consider them different 
enough to care which one is tuned.

Generally, it's a bad idea to have multiple *different* channels using 
the same channel number--meaning if the content of the broadcast differs 
(substantially) across the 2 channels, you should give them different 
numbers so that Live TV users can request the desired channel.  So, 
what's the tolerance of "substantially" when deciding whether the 
channels should have different numbers?  Well, it's up to the user--how 
important is it to be able to switch directly to the desired channel 
without going through a guide?  In my opinion, any difference in 
broadcast content other than "provider" ads counts as substantial.  On 
the other hand, having 2 channels with identical broadcast content and 2 
different channel numbers is perfectly acceptable--it allows the user to 
choose which one is tuned for Live TV, which may be handy if they're 
using different tuners/equipment and the user wants to be able to choose 
which equipment is used (i.e. to save using an STB or similar when not 
required).

And, when you have 2 channels with the same channel number, if they're 
given the same call sign, they will be "condensed" to a single line on 
the guide listings--meaning the channel will only show up once.  This is 
how you tell MythTV the 2 channels are the same channel--by setting both 
channel number and call sign to the same value on both channels.

Mike