07 Oct 2012

This is how to really understand video data rates

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A couple of years ago someone said to me, in all seriousness, “You know those things they used to call “Gigabytes”? Why do they call them “Terabytes” now?”.

My first reaction to this was to wonder how anyone could be so out of touch as to even think about asking a messed-up question like that, but then it occurred to me how easily mistakes like that can happen.

Part of the problem is that storage capacity is doubling every few years, and that while we might notice that the a 2TB drive is the same price as the 1TB drive we bought just over a year ago, what we fail to notice is that if you double capacity every year for several years, you quickly arrive at numbers that are not just a few times bigger, but thousands of times. When you factor in the price per gigabyte, you really do see some extraordinary figures.

Multiplication

For example, I bought a 1GB USB stick in 2002 for around $500. Now, you can buy a 16GB stick for around $8. That’s a thousand times cheaper per gigabyte in just ten years - the same multiplication factor as the difference between a gigabyte and a terabyte.

And it’s a good job that storage is growing like this, because raw video data rates are growing in the same way.

It’s hard to keep an intuitive grasp on data rates when they are just numbers. I prefer to think of them in terms of something I can see and touch. Books, for example. So, uncompressed standard definition video is around 10 copies of Tolstoy’s War and Peace per second - and that’s a large book. High definition video is around 50 copies per second. 4K video is four times this: 200 copies per second. Of course, if you double the framerate - as is likely to happen, to 60 fps. you double the data rate. That makes 400 copies per second, or 1,440,000 books per hour (1.44 “gigabooks” per hour).

4K and beyond

4K video is already here and we’re likely to see 8K video not long after that. Probably at a framerate of 120 fps. 8K video is not twice the data rate of 4K, it’s four times; 16 times the rate of “standard” HD. At 120 FPS that would mean 11,520,000 books per hour - so a 3 hour feature film would be the equivalent of 34,560,000 books. You’d need a really big storage device for those.

How about the US Library of Congress? Unfortunately that only has room for 22,765,967 books.

That’s right. An uncompressed 8K feature film at 120 FPS would need two Libraries of Congress to store that data if you were to print it out in hexadecimal and put it on shelves. It’s hardly surprising when you realise that every frame of an 8K video is effectively a 33 megapixel still photograph.

And to put it another way: within a few years, we’ll be able to store every book that’s ever been written on the hard disk (or SSD) in our laptop, or, more likely, our cellphone.

 


David Shapton

David is the Editor In Chief of RedShark Publications. He's been a professional columnist and author since 1998, when he started writing for the European Music Technology magazine Sound on Sound. David has worked with professional digital audio and video for the last 25 years.

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