[mythtv] mythtv-setup - DVB channel scanning

[roger]

I have been delving into DVB-T channel scanning in mythtv.

When using "full scan (tuned)" and the transport port scans with "search 
new transports" with a DVB_T tuner we often see the scanner trying to 
tune transports that are not physically receivable by the hardware. I 
looked into this and found that the code was not honouring the 
other_frequency_flag in the TerrestrialDeliverySystemDescriptor 
contained in the per transport stream loop in the Network Information 
Table (NIT). This flag means that this particular transport stream is 
also available on frequencies other than the one specified in the 
TerrestrialDeliverySystemDescriptor itself. Information on these other 
frequencies information should be found a FrequencyListDescriptor for 
this transport. The ETSI EBU standards mandate that this flag must be 
set if a ChannelListDescriptor is present but not that a 
ChannelListDescriptor must be present if this flag is set, which seems a 
little weird.

I plan to implement the following algorithm. I would appreciate comments 
on this.

1. If the other_frequency flag is present then (conditional on the usual 
stuff)  then go to step 2. otherwise use the centre frequency from the 
TerrestrialDeliverySystemDescriptor.

2. If the frequency I am actually tuned to is the same as the centre 
frequency from the TerrestrialDeliverySystemDescriptor then use it 
otherwise go to step 3.

3. If a FrequencyListDescriptor is present then go to step 4 otherwise 
use the centre frequency from the TerrestrialDeliverySystemDescriptor.

4. Add all the frequencies from the list to the list of new transports. 
Need to check if I can just do this blindly without ending up with 
duplicates when a new transports is tuned.


I may have to extra work for this to work here in the UK. I have checked 
the streams coming from my local transmitter. They have the 
other_frequency_flag set but do not contain any 
FrequencyListDescriptors. I know that they used to. Because I have seen 
them in traces. Has anyone got any information on this?


Roger