Bluray compression

aliEnRIK

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Im intrigued by what people on this forum believe about the bluray format

The standard format for bluray is H264 MPEG4 - a form of 'compression'

The same H264 standard can take a 20Gb bluray and 'compress' it down to 4Gb still running at 1080P.

When I play a bluray it can jump from next to no bitrate to around 20Mb/s. If video was truly uncompressed it would be constant and equal for EVERY 1080P bluray

If anyone here believes blurays are uncompressed im all ears
 
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Anonymous

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I didnt think anyone has ever said blu-rays were not compressed?! Or am i missing something?

I can imagine a completely uncompressed "RAW" 1080P 2 hour movie would be HUGE!
 

laserman16

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A single layer disc running a 90min film at say an average bitrate of 10MB/s would equate to about 52GB so I can't see how they can be uncompressed.
 

aliEnRIK

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watcher27:

I didnt think anyone has ever said blu-rays were not compressed?! Or am i missing something?

I can imagine a completely uncompressed "RAW" 1080P 2 hour movie would be HUGE!

Some have stated that video over HDMI (Of which ill take bluray as a prime example) as being uncompressed
 
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Anonymous

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You've gotten the wrong end of the stick!

They are talking about the HDMI protocol as a whole. ie, the signal being transmitted through HDMI is uncompressed, but the source may not be! If you get my drift?

So for example i play a compressed video file on my PS3 (DVD encode for example), its being sent as an uncompressed stream from the PS3 to the TV.

With blu-ray its the same. So the compressed blu-ray is uncompressed by the player, and the uncompressed stream sent through HDMI.

Ahh poo, im rubbish at explaining things!

Can someone else explain it better please
emotion-1.gif
 

aliEnRIK

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watcher27:

You've gotten the wrong end of the stick!

They are talking about the HDMI protocol as a whole. ie, the signal being transmitted through HDMI is uncompressed, but the source may not be! If you get my drift?

So for example i play a compressed video file on my PS3 (DVD encode for example), its being sent as an uncompressed stream from the PS3 to the TV.

With blu-ray its the same. So the compressed blu-ray is uncompressed by the player, and the uncompressed stream sent through HDMI.

Ahh poo, im rubbish at explaining things!

Can someone else explain it better please
emotion-1.gif


I understand where your coming from (although obviously HDMI is uncompressed in that form else it would have 2 forms of compression - hardly a great design)

But the same people claim that you cant have a single image displayed using the HDMI protocol without it using 'full bandwidth' all the time. Which is utter rubbish as you can send a single image and tell it to hold that image using the MPEG4 compression technique.

ie - if I held that image for 4 hours it would be almost the same amount of information being sent as a single image over the entire 4 hour period. The file size would be tiny.

if I sent the image continuously with every frame for 4 hours then bandwidth would go through the roof and the file would be infinately larger
 
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Anonymous

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aliEnRIK:watcher27:
You've gotten the wrong end of the stick!

They are talking about the HDMI protocol as a whole. ie, the signal being transmitted through HDMI is uncompressed, but the source may not be! If you get my drift?

So for example i play a compressed video file on my PS3 (DVD encode for example), its being sent as an uncompressed stream from the PS3 to the TV.

With blu-ray its the same. So the compressed blu-ray is uncompressed by the player, and the uncompressed stream sent through HDMI.

Ahh poo, im rubbish at explaining things!

Can someone else explain it better please
emotion-1.gif


I understand where your coming from (although obviously HDMI is uncompressed in that form else it would have 2 forms of compression - hardly a great design)

But the same people claim that you cant have a single image displayed using the HDMI protocol without it using 'full bandwidth' all the time. Which is utter rubbish as you can send a single image and tell it to hold that image using the MPEG4 compression technique.

ie - if I held that image for 4 hours it would be almost the same amount of information being sent as a single image over the entire 4 hour period. The file size would be tiny.

if I sent the image continuously with every frame for 4 hours then bandwidth would go through the roof and the file would be infinately larger

Ahhhh got ya
emotion-1.gif


Not really got that much into the techie side of it, i'll re read your posts and have a look around, then come back with my comments! lol
 

Paul.

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I've never heard bluray video called uncompressed. As you rightly say, h.264 is a standard for video compression (albeit a very good one). The original masters would be shot at significantly higher data rates than can be displayed by bluray, so it must be compressed.
 
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Anonymous

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Paul Hobbs:I've never heard bluray video called uncompressed. As you rightly say, h.264 is a standard for video compression (albeit a very good one). The original masters would be shot at significantly higher data rates than can be displayed by bluray, so it must be compressed.

I agree, 35mm film and super 35, both have higher resolution than 1080p, so it only makes sense that the video information on the blu ray is compressed i.e. Why H264 or similar has to be used. The sound is another matter however.

Also I think this is why the original Avatar blu ray release has very limited extras so the minimum possible compression was carried out to ensure the best possible picture, and why I think they are still working on high / multiple layered blu rays to hold more information.

Roll on 4K2K lol
 
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Anonymous

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Maybe this clarifies.

BD is stored in compressed form on a blu-ray disc

The player reads the disc at upto 54Mbps, decodes the video to uncompressed and outputs it along with the audio (which may still be compressed or uncompressed) over HDMI at a rate of upto 10.2Gbps.

An uncompressed BD would take up around 9,000GB for a 2hour film.
 
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Anonymous

Guest
As for how still images work - both u and Andrew are misunderstanding,

For a still image the graphics cards framebuffer does not change (graphics cards card work on deltas, as to whether or not the framebuffer needs to be updated) - but the framebuffer will be re-sent every frame regardless.

So as far as HDMI is concerned - there is no difference between still images and video, and thats why the test by Digital Foundry on expensive vs cheap HDMI cables is valid.

From an HDMI perspective the throughput on a still-image will be the same as sending video.
 

Cofnchtr

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Hi,

Does a still image not send a constant amount of information in each frame - whereas using a moving image, the amount of information requiring to be sent would (probably) change in every frame?

This would produce peaks and troughs to be sent along the HDMI cable at any given point in time as the amount of information between each frame changes?

If the above seems ignorant - it's because I am!!
emotion-1.gif


Cheers,

Cofnchtr.
 

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