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Old 02-01-2008, 02:52 PM   #1
emm7th emm7th is offline
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Default Blu-ray Maximum Bitrate Question...

I just have a question... is the bitrate for video directly proportional to the number of pixels in the screen? If yes, then why is BD's video bandwidth limited to 40Mbps while DVD's 9.8Mbps... note: BD's resolution is 6x the DVD's (1920x1080 vs 720x480)... any explanation?
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Old 02-01-2008, 02:55 PM   #2
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Bit rate is the amount of data that can be transfered at any time. Despite what the screen shows, the codec is important in limiting the bitrate. DVDs suffer severely from low bitrate, but Blu-ray has solved this problem.

This is more about data transfer and less about resolution. A codec can compress an image so the data is not as clear as it could be but will fit within a set bitrate.

http://en.wikipedia.org/wiki/Bit_rate#Video_.28MPEG2.29
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Old 02-01-2008, 02:59 PM   #3
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You can have 1080p resolution and a low bit rate.

It all has to do with the encoding process. The higher the bitrate the less entrusive the compression is.


Its a lot like the difference between someone saving a 5MP digital camera picture as a low quality Jpeg vs. an umcompressed Tiff file. Same resolution but much less compression with the Tiff file.

Also Blu-ray can process 48MBps while playing.

HD-DUD has a max of 30MBps. This includes both audio and video data on the same pipeline.
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Old 02-01-2008, 03:03 PM   #4
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Quote:
Originally Posted by emm7th View Post
I just have a question... is the bitrate for video directly proportional to the number of pixels in the screen? If yes, then why is BD's video bandwidth limited to 40Mbps while DVD's 9.8Mbps... note: BD's resolution is 6x the DVD's (1920x1080 vs 720x480)... any explanation?
are you sure it's limited to 40Mbps? The simpsons I think has more than that (42)
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Old 02-01-2008, 03:10 PM   #5
emm7th emm7th is offline
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The specs say that max video bitrate is 40Mbps & max data transfer rate is 54Mbps...
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Old 02-01-2008, 03:14 PM   #6
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Quote:
Originally Posted by emm7th View Post
The specs say that max video bitrate is 40Mbps & max data transfer rate is 54Mbps...
funny thing about it ka here how it goes the spec allows for 40mbs for video and 8 mbs for audio but as seen with pirates of the carriben (2 i think it was or 1) the bitrate went to over 50bmis in a couple scences also bee noted that i think it was the panisonic bd drive for laptop had an update to run the drive at x1.6 speed becuase movies wernt playing right
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Old 02-01-2008, 03:33 PM   #7
Neo65 Neo65 is offline
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Quote:
Originally Posted by emm7th View Post
The specs say that max video bitrate is 40Mbps & max data transfer rate is 54Mbps...
That spec is written mainly to factor in how fast the disk spins and how fast the data can be read from the disk. The jpeg analogy is the simplest way to understand different compression bitrates.

When you save a bitmap/photo under paintbrush or photoshop, you have an option of lower quality(=lower size) or higher (=higher bitrate).

If you take the same photograph and successively save it at lower and lower sizes, you have an idea if any artifacts are introduced into the compressed picture. (There will be). Some pictures will compress well without too many artifacts, others won't. Check the file sizes of each of the different types of pictures to see how they look when you do this.

Another way this works is with mp3s, you can have 64kbps mp3, you can also have 320kbps mp3. What is acceptable is a matter of personal preference, but it also depends on the kind of audio.

Last edited by Neo65; 02-01-2008 at 03:53 PM.
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Old 07-11-2008, 10:34 PM   #8
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Default Audio bitrate cap?

Under profiles 1 through 2, a/v bitrate is 48 Mbps combined audio and video, but video not to exceed 40Mbps.

Question: is the _audio_ bitrate similarly capped under these profiles, or is it technically within the spec to use all the 48Mbps for audio?

Say I just made an eight-channel 96/24 PCM recording. That's 24 bits times 96 kHz times 8 channels = 18.4 Mbps. This OK?

In theory do I have to stop there? Pretend Blu supported a hypothetical eight-channel one-bit 5.6 MHz codec. That would be 44.8 Mbps all for audio. Would this need a new profile?
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Old 07-11-2008, 10:37 PM   #9
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There will be no new profiles for settop players

Blu-ray has a max of 48mbps combined audio and video, of which 40 can be video, and 20 audio at any one time

You can put any combination of audio or video streams in there you want, so long as it doesn't exceed those limits.
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Old 07-11-2008, 10:39 PM   #10
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Quote:
Originally Posted by WickyWoo View Post
There will be no new profiles for settop players

Blu-ray has a max of 48mbps combined audio and video, of which 40 can be video, and 20 audio at any one time

You can put any combination of audio or video streams in there you want, so long as it doesn't exceed those limits.
20 it is. Thanks Wicky!
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Old 07-12-2008, 03:49 AM   #11
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Quote:
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There will be no new profiles for settop players
What will happen for 3D?
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Old 07-12-2008, 04:12 AM   #12
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3D will not be a "profile"
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Old 07-12-2008, 04:16 AM   #13
dialog_gvf dialog_gvf is offline
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Quote:
Originally Posted by emm7th View Post
I just have a question... is the bitrate for video directly proportional to the number of pixels in the screen? If yes, then why is BD's video bandwidth limited to 40Mbps while DVD's 9.8Mbps... note: BD's resolution is 6x the DVD's (1920x1080 vs 720x480)... any explanation?
It is directly proportional, but it isn't linear.

The average video bitrate of DVDs is somewhere in the 4-5Mbps range, with Superbits being 5-8Mbps. There certainly have been Blu-ray's exceeding 30Mbps average MPEG-2.

But, an entire scene isn't high detail. The codec only needs to worry about representing the high frequency portions, such as texture and edges, with the extra bits available to it.

The newer codecs (AVC and VC-1) are more efficient at representing the same restored picture with less bits than MPEG-2, so of course that needs to be taken into account too.

Gary
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Old 07-12-2008, 04:17 AM   #14
WickyWoo WickyWoo is offline
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9.8mbps was maximum BTW, 9.2 was the most you could hold sustained reliably. 9.8mbps also includes all audio, so the video track was often lower than what was reading
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Old 07-12-2008, 04:21 AM   #15
Deciazulado Deciazulado is offline
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Quote:
Originally Posted by emm7th View Post
I just have a question... is the bitrate for video directly proportional to the number of pixels in the screen? If yes, then why is BD's video bandwidth limited to 40Mbps while DVD's 9.8Mbps... note: BD's resolution is 6x the DVD's (1920x1080 vs 720x480)... any explanation?

Actually I'd say it could be up to 8x because to me most DVDs were mastered in 480i systems looking at interlaced CRTs

One factor to take into account is that DVD uses MPEG-2 while BD can use the more advanced MPEG-4 derivatives, VC-1 and AVC

So 40/9.8 = 4x the data rate, on more efficient codecs.

There's another factor. When you see a film image shrunk into DVD, as you're going from very high resolution to low resolution the chance is there that most parts of the image will be sharp overall. This even affects the depth of field of shots, and everything tends to look in focus as most of the image is reaching the DVD limit at once.

On a larger bigger image transfered from film to BD, there is more chance there will be more areas that could not be filled to the rim with detail and sharpness that reaches the resolution limits of BD. I remember when the first BDs came out, people started noticing focus points on films (shallower depth of field) and would ask why was not all the image in the frame in focus. That principle could account for a More Lossless Packing efficiency on occasion.

Having said that, I still think you should use the highest bitrate you can afford so people get no complaints from BDs thrown into 100" Home Theater screens which one day will be more common or even bigger ones. I remember when a 4:3 25" TV set in the living room was considered huge.. A luxury. Too much. Overpowering. Not necessary for enjoyment. Watch the SuperBowl on a 100" screen.

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Old 07-12-2008, 04:26 AM   #16
Branden Branden is offline
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Quote:
Originally Posted by jorg View Post
funny thing about it ka here how it goes the spec allows for 40mbs for video and 8 mbs for audio but as seen with pirates of the carriben (2 i think it was or 1) the bitrate went to over 50bmis in a couple scences also bee noted that i think it was the panisonic bd drive for laptop had an update to run the drive at x1.6 speed becuase movies wernt playing right

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Old 07-12-2008, 04:40 AM   #17
Simplayer Simplayer is offline
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I remember one of the insiders saying that for short bursts of time video could exceed 40mbps using some sort of buffer.

I'm not sure on the details.
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Old 07-12-2008, 05:46 PM   #18
dialog_gvf dialog_gvf is offline
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Quote:
Originally Posted by Simplayer View Post
I remember one of the insiders saying that for short bursts of time video could exceed 40mbps using some sort of buffer.

I'm not sure on the details.
Yes, it was insider 2themax, and he said they actually use that excess on occasion.

It's a bombshell that didn't go off during the BD/HD DVD war: A professional saying that even going beyond 40Mbps is helpful occasionally. Yet, the HGD DVD propaganda was that 24/26Mbps was excessive.

Gary
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