NG
That makes total sense. Presumably the Virgin Media DVB-C subsystem has a CAM that can decrypt multiple streams simultaneously (many can) so that recordings can be decrypted from the broadcast encrypted streams whilst live TV is also being decrypted from a different broadcast encrypted stream.
noggin
Founding member
The way that recordings work on Virgin Media boxes is different to the way that Sky do it. My understanding is that whilst the Sky boxes record the encrypted signal as broadcast, the Virgin Media boxes decrypt the signal, but then encrypt it again before saving to disk using a different system and an encryption key that's unique to each box (which is why you can't swap drives between boxes, they wouldn't be able to decrypt a recording made on a different box).
As there is no connection between the encryption system used to broadcast the channels and the system used to save recordings then technically there is no requirement to still be subscribed to a channel to play back a recording. For many years this is how it worked and you could continue to watch recordings from channels that you no longer subscribed to.
At some point Sky decided they didn't like this and required Virgin Media to change they system so that it behaved in the same way as the Sky boxes. This is the point where it went wrong as Virgin Media implemented the new system badly.
The way it works now is that there are restrictions placed on the channels from Sky, but not other broadcasters. The Sky channels are flagged so that the boxes know which channels to apply the restrictions to. When you go to play back a recording the box checks to see if the recording came from a channel that Sky own and if it does then it will only let you play the recording if you still subscribe to the channel. Unlike the Sky boxes there is no technical reason for this restriction, it's a contractual requirement imposed by Sky.
If a recording is from a non Sky channel then the check to see if you're still subscribed isn't done, so you should still be able to play back recordings from non Sky channels that you no longer subscribe to.
The problem is that in order for this check to work the channel still needs to be broadcasting on the system. Shortly after introducing this system a channel closed down and lots of people on various forums complained that they couldn't watch recordings from that channel any more. Because it was no longer broadcasting the check to see if it was flagged as a Sky channel couldn't be done, so the box refused to play back the recording.
As a result, when a channel on Virgin Media closes down it isn't completely removed from the system. The broadcast stops, but the channel remains in the channel tables as a hidden channel for awhile so that any recordings can still be watched. After some time (normally a few months, but it can vary) the channel is completely removed and recordings can no longer be played back.
This can cause a lot of problems, not only when people try to watch old recordings from channels that no longer exist, but also when changes are made to which regional version of a channel is broadcast, or where a channel has gone HD only with the SD version closing. Whilst viewers can still receive the channel, if it's not the exact same version (with the same ID) that the recording was made from then the recordings can't be played back.
As there is no connection between the encryption system used to broadcast the channels and the system used to save recordings then technically there is no requirement to still be subscribed to a channel to play back a recording. For many years this is how it worked and you could continue to watch recordings from channels that you no longer subscribed to.
At some point Sky decided they didn't like this and required Virgin Media to change they system so that it behaved in the same way as the Sky boxes. This is the point where it went wrong as Virgin Media implemented the new system badly.
The way it works now is that there are restrictions placed on the channels from Sky, but not other broadcasters. The Sky channels are flagged so that the boxes know which channels to apply the restrictions to. When you go to play back a recording the box checks to see if the recording came from a channel that Sky own and if it does then it will only let you play the recording if you still subscribe to the channel. Unlike the Sky boxes there is no technical reason for this restriction, it's a contractual requirement imposed by Sky.
If a recording is from a non Sky channel then the check to see if you're still subscribed isn't done, so you should still be able to play back recordings from non Sky channels that you no longer subscribe to.
The problem is that in order for this check to work the channel still needs to be broadcasting on the system. Shortly after introducing this system a channel closed down and lots of people on various forums complained that they couldn't watch recordings from that channel any more. Because it was no longer broadcasting the check to see if it was flagged as a Sky channel couldn't be done, so the box refused to play back the recording.
As a result, when a channel on Virgin Media closes down it isn't completely removed from the system. The broadcast stops, but the channel remains in the channel tables as a hidden channel for awhile so that any recordings can still be watched. After some time (normally a few months, but it can vary) the channel is completely removed and recordings can no longer be played back.
This can cause a lot of problems, not only when people try to watch old recordings from channels that no longer exist, but also when changes are made to which regional version of a channel is broadcast, or where a channel has gone HD only with the SD version closing. Whilst viewers can still receive the channel, if it's not the exact same version (with the same ID) that the recording was made from then the recordings can't be played back.
That makes total sense. Presumably the Virgin Media DVB-C subsystem has a CAM that can decrypt multiple streams simultaneously (many can) so that recordings can be decrypted from the broadcast encrypted streams whilst live TV is also being decrypted from a different broadcast encrypted stream.