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I don't know if this is the correct place to ask this type of question, but here is it. I wanted to find a ball park size of each blu-ray frame size in bytes. This is my calculation which cannot be correct.

Assuming we have a 2 hour blu-ray movie of size 25GB:

(25 * 1024) / (2 * 3600) = 3.56 MB/s of data

Blu-ray's fps ranges from 25-59 fps:

3.56 MB/s / 25 = 145 KB

That is around 145 KB for each 1910 x 1080 pixel picture?! I don't know what I'm doing wrong here...

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1 Answer 1

up vote 5 down vote accepted

What you are missing is that not every frame is stored as a picture. A large number of frames are stored simply by keeping track of what changed from the previous picture. If you think about most video, not a whole lot is actually changing since the majority of the scene stays the same or moves in a similar pattern. By describing only the changes, the amount of space required can be reduced drastically.

This is why the actual data "per frame" can be so low since only a fraction of the frames are actually full frames.

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That's part of what variable bit rate (VBR) compression is about. When there is almost no action, extremely little information is used, during high action sequences with fast cuts, substantially more bit rate is required. There is also an art in compression to determining how often different types of frames should be included. The frames can either be full images, differences or differences with corrections. –  AJ Henderson Apr 4 '13 at 14:58
    
really? So each frame would be a diff of the previous frame? How does it know when a scene completely changed so it would not use the diff to create the next frame. Does this mean a fast paced action scene of 5 minutes with potentially take more space than the 20 min dialogue scene in hunger? –  Armen B. Apr 4 '13 at 14:58
    
Do you know the name of this compression algorithm that blueray movies use? –  Armen B. Apr 4 '13 at 14:59
    
@ArmenB - yes, that is exactly what it means, but it could be even more substantial. It's entirely possible to see differences in required bitrate that can be 7 or 8 times more/less information. –  AJ Henderson Apr 4 '13 at 15:00
    
@ArmenB - H.264 (MPEG-4 derived) or H.262 (MPEG2 derived) mostly. VC-1 is the other standard that is required to be supported. –  AJ Henderson Apr 4 '13 at 15:00

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