PDC equivalent on DVBS? (for recording delayed transmissions) (1 Viewer)

[RobNorthcott]

Something that I miss from the good old analogue VHS recorder is PDC (Programme Delivery Control I think), where a little time signal was sent at the start and end of programmes and the machine could detect if things were running late and compensate for it.

I assumed the technology just didn't exist in DVB, but the subject came up in conversation yesterday (sad I know) and my brother-in-law says his Sky+ box has that very feature. So is there any way it could be done in MP?

Rob

 

[allanp81]

I think it does exist in DVB-T as my dad's freeview box starts recording the programme just as it starts.

 

[RobNorthcott]

Yes, I think something like that must exist in the DVB-S signal as well (because Sky+ apparently does it). But I haven't heard anything about MP using it - I wonder if it's extremely hard to deal with or something...

Anybody who knows about the DVB decoding side of MP reckon it's doable?

Rob

 

[Paul Shirley]

For UK Freeview+ in theory you just monitor the EPG Now&Next stream and record when it matches the scheduled programme (other + features need more tables parsed and auto tracking is more efficient if you grab the programme identifier from them). You need to grab a tuner 15min before transmission (any mux) and on enabled channels the Now&Next will track time changes.

In practice its not so easy because less than half of the channels support Freeview+ so that tracking guarantee isn't trustworthy (including all radio channels). Ideally you want to speculatively start recording early and continue past the end to pad channels that don't support + and support is so variable I'd want padding even on + channels. My PVR persistently clips 10-30sec from the start of programmes because the signal is sent just-in-time - leaving no time for the badly designed box to tune quickly enough.

I'd say its doable by hacking the EPG update code, doing it well is a whole different problem.