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How does PVR know when to record?


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Old 23-12-2010, 16:11
Penners
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As a relative newcomer to hard drive recording, I'm interested to know how the Foxsat PVR knows when to start and stop recording.

It's clearly not triggered by a clock, because if the programme is delayed, the machine still captures it all, starting and stopping correctly.

So is there some sort of signal broadcast at the beginning and end of every programme, which tells the machine when to start and stop?

I'd love to know the technicalities (in simple terms!) please.
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Old 23-12-2010, 16:20
brumlad36
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As a relative newcomer to hard drive recording, I'm interested to know how the Foxsat PVR knows when to start and stop recording.

It's clearly not triggered by a clock, because if the programme is delayed, the machine still captures it all, starting and stopping correctly.

So is there some sort of signal broadcast at the beginning and end of every programme, which tells the machine when to start and stop?

I'd love to know the technicalities (in simple terms!) please.
It uses a system called "Accurate Record". The signal is sent over the air by the broadcaster, similar to PDC (which was used for analogue VCRs). As I understand it, sometimes the broadcaster fails to send the "start" command, and then everyone's recording fails!

Chris.
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Old 23-12-2010, 16:31
Jarrak
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I'd love to know the technicalities (in simple terms!) please.


The EPG (Electronic Programme Guide) is what makes a PVR really work, it's basically a database of programming including start/stop times, synopsis etc when resides on the PVR's internal memory or cached to the hard drive and is updated over the air in real time. The TIVO, SKY+, V+, Freeview and Freesat PVR's all rely on an EPG (each specific to the product) to make them work were as "dumber" recorders may only have access to a now&next data stream limiting their use except of manual recording based on the timer.
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Old 23-12-2010, 16:32
grahamlthompson
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All the freesat channels transmit what's on now and what's coming up next along with the pictures (Now/Next). The hdr wakes up 15 mins before the recording is due and watches for the now/next to change to the programme you wan't to record. The same thing happens at the end of the programme. As already said to work properly the broadcaster has to send the right codes.

To watch it in action bring up the schedule list a few minutes before a recording is due to start, you can see the recording start with the picture in the background. ITV for instance usually send the start as the opening credits start and the end after the ads at the end of the programme.
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Old 23-12-2010, 16:34
gagde
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It uses a system called "Accurate Record". The signal is sent over the air by the broadcaster, similar to PDC (which was used for analogue VCRs). As I understand it, sometimes the broadcaster fails to send the "start" command, and then everyone's recording fails!

Chris.
Very true out off all makes off boxes i have had whether its skys/virgins or even vcrs the humax foxsat is probably the best one out of the lot even though we have virgin as well the foxsat has been used the most for recording its taken some hammer over the last few days recording 4 or 5 programmins a day and hasn't let us down yet the v+ a couple of fails.
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Old 23-12-2010, 16:39
LightningIguana
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I got sick of failures using the over air signal. Now I go the laborious route of setting the timer, just like VCR. Boo
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Old 23-12-2010, 16:41
Frank1
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As a relative newcomer to hard drive recording, I'm interested to know how the Foxsat PVR knows when to start and stop recording.

It's clearly not triggered by a clock, because if the programme is delayed, the machine still captures it all, starting and stopping correctly.

So is there some sort of signal broadcast at the beginning and end of every programme, which tells the machine when to start and stop?

I'd love to know the technicalities (in simple terms!) please.
No-one has thrown this in so I will.

Each programme change is an "event". There is a "Running Status Flag" which is part of the data associated with the programme stream. This changes when the event starts and stops.
Frank
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Old 23-12-2010, 16:49
Penners
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Well, thanks very much to you all for that very comprehensive explanation. My curiosity is well satisfied!

Have a great Christmas everyone!
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Old 23-12-2010, 16:56
gagde
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Well, thanks very much to you all for that very comprehensive explanation. My curiosity is well satisfied!

Have a great Christmas everyone!
And you happy recording.
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Old 23-12-2010, 17:52
Jepson
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I got sick of failures using the over air signal. Now I go the laborious route of setting the timer, just like VCR. Boo
Failures are mainly down to the broadcasters not transmitting the appropriate signals (or just not bothering to transmit the programme*), rather than the PVR itself.

You'd probably be better off still using the EPG but using 'padding' instead of accurate recording.




* For some reason I had the recent BBC series 'Single Father' set to record the later repeat (I think I missed setting the first episode at the 21:00 transmission so set series record on the later).

They didn't transmit the final programme in the later slot despite it being set up as a separate series.
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Old 23-12-2010, 21:22
Bob_Cat
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There are three levels of signalling:
EIT schedule - this is what forms the Electronic Programme Guide and has all the events. Traditionally (in freeview) the guide is broadcast in multiple loops, the more current events are looped quicker and later events are looped at slower rates. In the case of freesat the entire EPG is broadcast very quickly and is downloaded by the STB occasionally to update it's internal copy (typically when you select the EPG or over night).
EIT present-following - this is broadcast along with the channels and sends the current and next events for every channel and is frequently cycled. In the case of freesat more than just present and following is sent. (also known as Now/Next)
Running Status - This tells the recorder when an event starts, the device knows when the event ends because the next event starts. (also known as Accurate Record Trigger).

Some products keep these three elements separate and often the info-plate, which is shown when you press "i" while watching TV, will just show the EIT present-following and nothing more. More modern set-top boxes and recorders can keep the entire schedule in memory and products like the Foxsat update the schedule database with the PF data rather than keep the data separate.

Bob
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Old 24-12-2010, 08:49
Automan
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There are three levels of signalling:
EIT schedule - this is what forms the Electronic Programme Guide and has all the events. Traditionally (in freeview) the guide is broadcast in multiple loops, the more current events are looped quicker and later events are looped at slower rates. In the case of freesat the entire EPG is broadcast very quickly and is downloaded by the STB occasionally to update it's internal copy (typically when you select the EPG or over night).
EIT present-following - this is broadcast along with the channels and sends the current and next events for every channel and is frequently cycled. In the case of freesat more than just present and following is sent. (also known as Now/Next)
Running Status - This tells the recorder when an event starts, the device knows when the event ends because the next event starts. (also known as Accurate Record Trigger).

Some products keep these three elements separate and often the info-plate, which is shown when you press "i" while watching TV, will just show the EIT present-following and nothing more. More modern set-top boxes and recorders can keep the entire schedule in memory and products like the Foxsat update the schedule database with the PF data rather than keep the data separate.

Bob
Cool detail

It is a shame they did not include a program end signal rather than having to wait for the next program to start.

Plus of course ITV seem to forget to correct this data when they break programs up into two parts and show them on seperate days.

e.g. A Touch Of Frost and Midsummer Murders.

Automan.
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Old 31-12-2010, 19:15
Ardee
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Well, I must say that the system is a lot cruder than I expected. PDC was far more sophisticated.

Since we are stuck with it, I suppose what is needed now is a requirement for broadcasters to explain each and every event failure to to the regulator, along with fines for poor performance.
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Old 02-01-2011, 13:49
spiney2
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event information - specific to the Freeview system only - is sent in the "misc info" field of the mpeg2 muxed streams. As is the epg. However, now/next is a standard feature on DVB/t terrestrial digital

It;s this that caused so many problems on the Vestel PVRs (and again last night ,although thankfully, for 1 night only!).
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Old 02-01-2011, 15:15
Flyer 10
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I got sick of failures using the over air signal. Now I go the laborious route of setting the timer, just like VCR. Boo
I missed more programs due to them overrunning when I did that, stuff like F1 or football means you miss the ET or delayed race if you do a manual timer.

Of course if its on ITV, you lose the recording either way as your time will be wrong and they never update the EPG so you have to record what on after to be sure.
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