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How does PVR know when to record? |
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#1 |
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Forum Member
Join Date: Dec 2010
Posts: 11
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How does PVR know when to record?
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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#2 |
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Forum Member
Join Date: Mar 2008
Location: Lincoln (Belmont/Waltham TXs)
Posts: 2,344
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Quote:
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. Chris. |
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#3 |
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Forum Member
Join Date: Jan 2002
Location: Ilkeston
Posts: 18,075
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Quote:
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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#4 |
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Forum Member
Join Date: May 2005
Location: Redditch Worcs
Posts: 17,287
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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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#5 |
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Forum Member
Join Date: Oct 2000
Location: staffs
Posts: 3,808
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Quote:
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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#6 |
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Forum Member
Join Date: Mar 2006
Location: Under your bed...
Posts: 15,706
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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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#7 |
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Forum Member
Join Date: Oct 2003
Location: Devon UK
Posts: 355
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Quote:
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. 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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#8 |
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Forum Member
Join Date: Dec 2010
Posts: 11
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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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#9 |
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Forum Member
Join Date: Oct 2000
Location: staffs
Posts: 3,808
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Quote:
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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#10 |
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Inactive Member
Join Date: Oct 2009
Posts: 3,089
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Quote:
I got sick of failures using the over air signal. Now I go the laborious route of setting the timer, just like VCR. Boo
![]() 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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#11 |
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Forum Member
Join Date: Apr 2005
Location: Surrey, UK
Posts: 1,302
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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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#12 |
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Forum Member
Join Date: Sep 2001
Location: South Coast, UK
Posts: 4,952
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Quote:
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 ![]() 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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#13 |
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Forum Member
Join Date: Dec 2003
Posts: 121
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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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#14 |
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Forum Member
Join Date: Jul 2010
Posts: 24,096
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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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#15 |
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Forum Member
Join Date: Dec 2008
Posts: 4,556
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Quote:
I got sick of failures using the over air signal. Now I go the laborious route of setting the timer, just like VCR. Boo
![]() 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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