<p>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.</p>

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

CC BY-SA 3.0
2013-04-04T14:58:23.037Z
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
CC BY-SA 3.0
2013-04-04T14:58:36.250Z
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 Babakanian
CC BY-SA 3.0
2013-04-04T14:59:41.833Z
Do you know the name of this compression algorithm that blueray movies use?
Armen Babakanian
CC BY-SA 3.0
2013-04-04T15:00:11.123Z
@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
CC BY-SA 3.0
2013-04-04T15:00:31.437Z
@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
CC BY-SA 3.0
2013-04-08T05:35:54.440Z
@AJHenderson This make a lot more sense than my answer! I am curious to know how the player knows what parts of which frames to combine? Is there info that tells it, or does it just keep adding until a full frame comes along?
OrangeBox
CC BY-SA 3.0
2013-04-08T13:14:38.300Z
@OroangeBox - I'm less sure about that part, particularly since I think it can very by format.  For DVDs for example (if my memory serves), there was a repeating pattern that was setup in the header of I,B and P frames.  Typically the pattern would be about 15 frames in length, but the length and pattern and even number of each type of frame could be altered.  I think it was also able to be pieced together on the fly though if necessary (for example if the header is corrupted) but I'm not sure if that is simply from a guess or if there is an actual deterministic way.
AJ Henderson
CC BY-SA 3.0
2013-04-04T04:40:28.177Z
2013-04-04T04:40:28.177Z
AJ Henderson
<p>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.</p>

<p>Assuming we have a 2 hour blu-ray movie of size 25GB: </p>

<p><code>(25 * 1024) / (2 * 3600) = 3.56 MB/s of data</code></p>

<p>Blu-ray's fps ranges from 25-59 fps: </p>

<p><code>3.56 MB/s / 25 = 145 KB</code></p>

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

<compression><video-quality><storage><bluray>
Bluray I/O speed
Armen Babakanian
# Bluray I/O speed

(Asked by: username_0 on 2013-04-04)

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...

**Tags:** compression, video-quality, storage, bluray


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## 1 answers

### Answer by username_1 on 2013-04-04. Score: 5 | Accepted answer

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.

> **Comments:**
> **username_1**: 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.  
> **username_0**: 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?  
> **username_0**: Do you know the name of this compression algorithm that blueray movies use?  
> **username_1**: @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.  
> **username_1**: @ArmenB - H.264 (MPEG-4 derived) or H.262 (MPEG2 derived) mostly.  VC-1 is the other standard that is required to be supported.  
> **username_2**: @AJHenderson This make a lot more sense than my answer! I am curious to know how the player knows what parts of which frames to combine? Is there info that tells it, or does it just keep adding until a full frame comes along?  
> **username_1**: @OroangeBox - I'm less sure about that part, particularly since I think it can very by format.  For DVDs for example (if my memory serves), there was a repeating pattern that was setup in the header of I,B and P frames.  Typically the pattern would be about 15 frames in length, but the length and pattern and even number of each type of frame could be altered.  I think it was also able to be pieced together on the fly though if necessary (for example if the header is corrupted) but I'm not sure if that is simply from a guess or if there is an actual deterministic way.  

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