[guy jones] "thanks this is really good info. To get back to the size of the original, when I say it's 10mb, I mean that's the .MOV file directly from the camera, so shouldn't that be the max size it will ever be?"
Nope. The uncompressed version of that file will be bigger. Uncompressed doesn't mean no additional compression -- it means no compression whatsoever.
There's a lot to video compression, but basically, lossy video compression like H.264 throws away visual information to reduce the file size. It rounds off values. It ignores subtle differences in color. It approximates shapes or movement. It eliminates visual redundancies. Basically, it cheats. What you end up with is not what you started with.
Uncompressed video stores the exact value of every single pixel of every frame of video. It doesn't look for efficiency. It doesn't eliminate redundancy. It doesn't matter what the content is: even a full black field will store RGB [0,0,0] for every single pixel. A full uncompressed black frame will take the same amount of storage that a complicated image would.
So why does the file size grow when you go from compressed video to uncompressed?
Compressed video is just data. It doesn't look like a picture until it is decoded, and once it is decoded, the computer treats it as a series of uncompressed frames again in order to display or process it.
When you save that out as uncompressed, all the decoded pixel values are saved -- not the original data from the compressed frame. This doesn't improve the quality of the compressed original, but it does preserve it, precisely.
Here's a little math. Let's calculate the storage requirements for one second of uncompressed RGB video at 720p60.
The frame size is 1280x720, and each pixel is 24 bits (8 bits each for red, green, and blue values). That means every frame is 1280x720x24 bits, or a little more than 22 million bits, or about 2.6 megabytes. Since a second has 59.94 frames, we can multiply 2.6 MB * 59.94 to get 158 megabytes per second.
Our uncompressed file is 158 MB. It doesn't matter what the content is or how it originated; because we are storing all the RGB values of every single pixel, any picee of content 8-bit 720p60 content, no matter what its origin, must be 158 MB when saved as uncompressed RGB.
Walter Soyka
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