How Video On Demand Works (long and technical!)
12-01-2005, 10:31
|
#16
|
|
cf.mega poster
Join Date: Jun 2003
Posts: 9,018
|
Re: How Video On Demand Works (long and technical!)
Quote:
|
Originally Posted by ianathuth
Would it be possible to supply the normal digital channels using the same method as VOD but without the pause, rewind, etc. that VOD has? That is just transmitting the live pictures from the selected channel to your TV.
|
Yes, it's known as Broadcast On Demand (BOD). See here for a presentation. (Although that's not about cable, the same principle applies).
"There goes Bod..."
|
|
|
|
12-01-2005, 13:38
|
#17
|
|
Mum 30/09/20 Dad 08/08/24
Join Date: Mar 2004
Location: Galactic Sector ZZ9 Plural Z Alpha, A secret Moonbase (shh don't tell anybody)
Age: 56
Services: 2 x TiVo 360s, SH5. Samsung Galaxy Note 10+ 5G, Ton's of Smart Home stuff, & Cuddy Toy
Posts: 17,257
|
Re: How Video On Demand Works (long and technical!)
Forgive my if I'm being stupid but to rewind/pause VOD doesn't the STB use a hard drive in it recording the last 30 mins or so??
__________________
I'm a Trustee & Secretary for a local charity
STAY AT HOME: I found out that mum will never walk again as the coronavirus attacked her nervous system. She died on September 30th.
|
|
|
|
|
12-01-2005, 14:02
|
#18
|
|
Inactive
Join Date: Jun 2003
Location: South-East-Cambridge
Services: ntl digital basepack
ntl 1M broadband
Posts: 1,068
|
Re: How Video On Demand Works (long and technical!)
Quote:
|
Originally Posted by david.ewles
Forgive my if I'm being stupid but to rewind/pause VOD doesn't the STB use a hard drive in it recording the last 30 mins or so??
|
No, it just requests that video stream is rewound or paused and requests the play is started again from the point when play is pressed in much the same way as a Real Video stream works on the internet.
What you are thinking about is a PVR, which records live TV broadcasts on a hard drive.
|
|
|
|
|
12-01-2005, 15:44
|
#19
|
|
Inactive
Join Date: Jun 2003
Location: Manchester
Posts: 5,638
|
Re: How Video On Demand Works (long and technical!)
I think some freeview boxes record the last 30 mins or seconds (cant remember which) into internal memory - perhaps that's what he's thinking of.
|
|
|
|
|
12-01-2005, 16:43
|
#20
|
|
Inactive
Join Date: Jun 2003
Location: South-East-Cambridge
Services: ntl digital basepack
ntl 1M broadband
Posts: 1,068
|
Re: How Video On Demand Works (long and technical!)
Quote:
|
Originally Posted by etccarmageddon
I think some freeview boxes record the last 30 mins or seconds (cant remember which) into internal memory - perhaps that's what he's thinking of.
|
There are a number of Freeview PVRs available, some with dual-tuners like Sky+, from around £150 that offer "Pause Live TV" as an option. These work by buffering up to 30 minutes of video from the currently viewed channel.
They also offer the recording to hard drive feature of all PVRs. Hopefully, the new NTL PVRs will offer the same features when they are released at the end of the year.
|
|
|
|
|
12-01-2005, 16:53
|
#21
|
|
cf.member
Join Date: Oct 2003
Location: London
Posts: 7
|
Re: How Video On Demand Works (long and technical!)
Quote:
|
Originally Posted by bob_builder
No, it just requests that video stream is rewound or paused and requests the play is started again from the point when play is pressed in much the same way as a Real Video stream works on the internet.
What you are thinking about is a PVR, which records live TV broadcasts on a hard drive.
|
When a movie is loaded on to a VOD server for the first time, "trick-play" files are generated. One is just an MPEG of your movie being played fast-forward at 6-7x speed, and another is an MPEG of your movie going backwards. These files, and the main movie file, are all cross-indexed together with respect to time.
When you REW or FF, the server stops playing out the main movie, and switches to playing out the appropriate trick play file, from the appropriate index point.
This saves a huge amount of CPU load on the server, freeing up more capacity for normal playback: generating the FF/REW image on the fly is a fairly expensive process.
|
|
|
|
|
12-01-2005, 17:20
|
#22
|
|
Inactive
Join Date: Jun 2003
Location: Manchester
Posts: 5,638
|
Re: How Video On Demand Works (long and technical!)
Quote:
|
Originally Posted by bob_builder
There are a number of Freeview PVRs available, some with dual-tuners like Sky+, from around £150 that offer "Pause Live TV" as an option. These work by buffering up to 30 minutes of video from the currently viewed channel.
They also offer the recording to hard drive feature of all PVRs. Hopefully, the new NTL PVRs will offer the same features when they are released at the end of the year.
|
no, I've actually seen a freeview box in a shop which isnt a PVR but which has a short 'pause' facility via a small in built buffer (unless it was labelled incorrectly in the shop!). perhaps that's what this bloke was thinking of.
|
|
|
|
|
12-01-2005, 17:38
|
#23
|
|
Inactive
Join Date: Jun 2003
Location: Glastonbury!
Services: Telewest DTV & 4Meg BB (Bath), NTL DTV and 2Meg BB (Poole)
Posts: 1,350
|
Re: How Video On Demand Works (long and technical!)
Quote:
|
Originally Posted by wir3d
When a movie is loaded on to a VOD server for the first time, "trick-play" files are generated. One is just an MPEG of your movie being played fast-forward at 6-7x speed, and another is an MPEG of your movie going backwards. These files, and the main movie file, are all cross-indexed together with respect to time.
When you REW or FF, the server stops playing out the main movie, and switches to playing out the appropriate trick play file, from the appropriate index point.
This saves a huge amount of CPU load on the server, freeing up more capacity for normal playback: generating the FF/REW image on the fly is a fairly expensive process.
|
I was told about this after I posted the big long thing above. Decided not to include it as I couldn't think of a way to put it consisely, but you've done a grand job there 
|
|
|
|
|
12-01-2005, 18:33
|
#24
|
|
Inactive
Join Date: Jun 2003
Location: South-East-Cambridge
Services: ntl digital basepack
ntl 1M broadband
Posts: 1,068
|
Re: How Video On Demand Works (long and technical!)
Quote:
|
Originally Posted by etccarmageddon
no, I've actually seen a freeview box in a shop which isnt a PVR but which has a short 'pause' facility via a small in built buffer (unless it was labelled incorrectly in the shop!). perhaps that's what this bloke was thinking of.
|
Ah! I have not seen those myself, but I guess the technology is the same as the PVR just using a memory buffer rather than a hard drive. However, you would need a lot of memory to store 30 minutes of video so I guess it would be a smaller buffer period.
|
|
|
|
|
12-01-2005, 20:34
|
#25
|
|
Inactive
Join Date: Jun 2003
Services: xl phone & xl tv 2mb broadband £34.95pence
Posts: 1,229
|
Re: How Video On Demand Works (long and technical!)
when is it being rolled out in bromley ? 
how will we know we have got it ?
will it rearange my channel list ?
|
|
|
|
|
12-01-2005, 20:37
|
#26
|
|
Inactive
Join Date: Jun 2003
Location: Glastonbury!
Services: Telewest DTV & 4Meg BB (Bath), NTL DTV and 2Meg BB (Poole)
Posts: 1,350
|
Re: How Video On Demand Works (long and technical!)
Don't know
Everything will be blue (again)
No
|
|
|
|
|
12-01-2005, 20:55
|
#27
|
|
Inactive
Join Date: Jun 2003
Services: xl phone & xl tv 2mb broadband £34.95pence
Posts: 1,229
|
Re: How Video On Demand Works (long and technical!)
why that little smile at the end ?
im feeling nervous now
|
|
|
|
|
12-01-2005, 21:15
|
#28
|
|
Inactive
Join Date: Jun 2003
Location: Renfrewshire, Orig-NTL
Posts: 59
|
Re: How Video On Demand Works (long and technical!)
Quote:
|
Originally Posted by bob_builder
Ah! I have not seen those myself, but I guess the technology is the same as the PVR just using a memory buffer rather than a hard drive. However, you would need a lot of memory to store 30 minutes of video so I guess it would be a smaller buffer period.
|
The Fusion FRT101 has a 30 seconds channel buffer for rewinding live TV.
Thanks for the post Tristan, I had always wondered where all this bandwidth was coming from, obviously localistation is the key. Cunning
|
|
|
|
|
13-01-2005, 20:03
|
#29
|
|
I try to help.
Join Date: Aug 2003
Location: Hove
Age: 37
Services: Virgin Media VIP - 2 x V6, M350 & phone
Posts: 288
|
Re: How Video On Demand Works (long and technical!)
Quote:
|
Originally Posted by paul11974
why that little smile at the end ?
im feeling nervous now
|
He's just a friendly guy 
|
|
|
|
|
14-01-2005, 13:00
|
#30
|
|
Inactive
Join Date: Jun 2003
Location: Derby / Stafford
Age: 38
Posts: 154
|
Re: How Video On Demand Works (long and technical!)
great post tristan. cheers 
Any news on content for launch?
|
|
|
|
Posting Rules
|
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts
HTML code is Off
|
|
|
All times are GMT +1. The time now is 14:26.
|
Join CF
You are here: 
