Hd Bandwidth ?

kirk1690 · 06-05-2008, 16:40

just how much extra space does an hd recording take up? ,I was under the impression it was 3 times as much as standard but i recently recorded a 2 hour film and it took up a whopping 11 hours space on the disk.

jem · 06-05-2008, 16:44

Quote:

Originally Posted by kirk1690

just how much extra space does an hd recording take up? ,I was under the impression it was 3 times as much as standard but i recently recorded a 2 hour film and it took up a whopping 11 hours space on the disk.

I guess you are talking about National Treasure or Indiana Jones. I recorded them both, never seen the free space indicator on the V+ say 'Critical' before. I also thought it was between three and four times the space requirements of SD-I wonder how accurate the free space indicator is.

darthlinux · 06-05-2008, 17:01

V+ can handle 80Hrs recording in SD and 20Hrs in HD

JethroUK · 06-05-2008, 17:16

I noticed National Treasure took up a whooopin 9 hours - that makes it about 4 times the space - actually i remember reading somewhere that HD does deliver 4 times as much information - so that would be about right & tallies with darthlinux findings

SMHarman · 06-05-2008, 19:48

Quote:

Originally Posted by JethroUK

I noticed National Treasure took up a whooopin 9 hours - that makes it about 4 times the space - actually i remember reading somewhere that HD does deliver 4 times as much information - so that would be about right & tallies with darthlinux findings

HD
720p = 1280*720 = 921,600 Pixels
1080i = 1920*1080 = 1,382,400 Pixels
SD
720*480 = 345,600 Pixels < for information only - US format
720*576 = 414,720 Pixels

1382400/414720 = 3.333 times more data in an HD image
Transitions, encoding level of action will then also impact the size of the file etc.

kirk1690 · 06-05-2008, 21:06

Quote:

Originally Posted by jem

I guess you are talking about National Treasure or Indiana Jones. I recorded them both, never seen the free space indicator on the V+ say 'Critical' before. I also thought it was between three and four times the space requirements of SD-I wonder how accurate the free space indicator is.

not very accurate I suspect

Losttheplot · 06-05-2008, 21:11

Quote:

Originally Posted by SMHarman

HD
720p = 1280*720 = 921,600 Pixels
1080i = 1920*1080 = 1,382,400 Pixels
SD
720*480 = 345,600 Pixels < for information only - US format
720*576 = 414,720 Pixels

1382400/414720 = 3.333 times more data in an HD image
Transitions, encoding level of action will then also impact the size of the file etc.

Also bear in mind most of the SD is variable bit rate (VBR), whereas the BBC HD will be constant bit rate (CBR) of around 18Mb/s.
I dont know what Virgin use for their HD VOD bitrates, but the SD VOD was done at 2.9Mb/s (CBR) from memory.

SMHarman · 06-05-2008, 23:15

Quote:

Originally Posted by Losttheplot

Also bear in mind most of the SD is variable bit rate (VBR), whereas the BBC HD will be constant bit rate (CBR) of around 18Mb/s.
I dont know what Virgin use for their HD VOD bitrates, but the SD VOD was done at 2.9Mb/s (CBR) from memory.

Thats a lot of Bandwidth for BBC HD when you consider HD DVDs run at a maximum of 30Mbit/s

Losttheplot · 07-05-2008, 07:13

Quote:

Originally Posted by SMHarman

Thats a lot of Bandwidth for BBC HD when you consider HD DVDs run at a maximum of 30Mbit/s

Thats MPEG2 for you, HD requires a lot of bandwidth! As Virgin are encoding a single channel and its MPEG2 HD then theres no room to stat mux, so they have to use CBR.

A single qam64 channel carries just over 38Mb/s so its not that much really, still plenty of room for a few SD channels.

Not sure what level and profile is typically used for HD DVD's - but level 4 for main profile defines a max of 20Mb/s - level 4.1 at main profile allows upto 50Mb/s to be used. Also bear in mind Virgin encode realtime with effectively a single pass best effort encode, DVD's are encoded non-realtime and for difficult scenes the encoding can be tweaked to provide the best results on a scene by scene basis.

SMHarman · 07-05-2008, 14:00

I was also looking at it vis a vis the 4 times the data so compared to an SD channel of 3Mb/s that would be 12Mb/s and they have a spare 6 Mb/s capacity there.

Those numbers are huge. That means I am getting 40*(say mid point of 15) Mb/s of HD content pushed down my cable here. Thats over 600+Mb/s. Then the 100s of SD channels also!

Losttheplot · 07-05-2008, 14:32

Quote:

Originally Posted by SMHarman

I was also looking at it vis a vis the 4 times the data so compared to an SD channel of 3Mb/s that would be 12Mb/s and they have a spare 6 Mb/s capacity there.

Those numbers are huge. That means I am getting 40*(say mid point of 15) Mb/s of HD content pushed down my cable here. Thats over 600+Mb/s. Then the 100s of SD channels also!

12Mb/s HD on MPEG2 would not be particularly good. H.264 HD is reasonable at those rates, but would still demand more for difficult scenes.
Virgin had at least 27 streams of over 38Mb/s each over 3 years ago so the numbers are feasible.