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Compressing Conversations

He was touting the merits of compression,. Compression was important, he would say, because it gave the ability to take something big, and break it down into much smaller parts, and then throw away what wasn’t needed or could be rebuilt later. He compared it to a large balloon that you wanted to store in a matchbox. If the balloon was full of air, it would never fit, but if you let out all the air and folded it up, there was no problem. You could store the balloon in a small space until you wanted to take it out and blow it up again.

‘…And so when the world of digital video caught on to the idea, everything started to change. The professionals started using DIGI-BETA instead of regular Beta SP and on the consumer market there was this great little thing called ‘DV’ - which is actually it’s own CoDec, with a particular frame- size, frame-rate and so on. The reason it took off so well was because you got the real world, squished it with a five to one compression, and stored it on these tiny little tapes called mini- DV.

‘Then there was the whole call to actually be able to edit delivery formats, like Mpeg2, and H.264 came along SLRs started shooting in it ….’ 

Shaun kept forward in the darkness. He was holding Lauren’s hand, and she was holding Giovanni’s. They had also tied themselves loosely together with a piece of string that Shaun had conveniently packed in anticipation of this moment. The cave dark was eerie, and it was only David’s endless rabble which kept them moving in the right direction.

Shaun kept close enough that he could still see the lights of the bug, but  did not help with what was immediately in front of them. They felt their way along blindly as if reading giant Braille. Ahead, David was still talking.

‘… you see with a regular acquisition format, you can access every frame of video so you can edit it, but with a delivery format, you don’t have that option. They use temporal compression, or compression over time.’

‘As opposed to spatial compression?’ the other voice cut in. Giovanni and Lauren were shocked to realize that the earlier version of Shaun had been following every word David was saying. They certainly had not.

‘That’s right! Spatial compression takes similar pixels, and actually just calls them the same thing. So, instead of having five shades of red, it only shows one. You lose some picture quality, of course, but the saving on your data-rate is massive. The advantage of adding temporal compression, is that the codec takes a frame, say frame one, and then takes another frame, say frame twelve, and fully compresses them. Then it looks at all the frames in the middle, and only compresses the changes. Anything that stays the same, it just repeats.’

‘That’s clever!’ Shaun said impressed.

‘It is, but it gets much better. There’s a new experimental type of compression that looks and not only says, ‘What’s repeated here?’ but also, ‘What could possibly be repeated if I spun it around a bit?’ So like it might take a fraction of a wall from one building, then look at the rest of the picture, and find, if it spins that fraction of the wall in a few different ways, that there are two hundred and thirty other places that little wall also fits! It files that were like 20 Meg, and compresses them to like 2 kilobytes!’

Shaun was no computer expert, but his did know his bits from his bytes. He knew that it took one thousand and twenty-four kilobytes to make a megabyte, and if what David was saying was true then this compression was reducing information to one ten-thousandth its size! You didn’t have to be a genius to appreciate that. Luckily, Shaun was a genius.

‘I was, after I left Newcom, playing with the same compression for video, and then in three-dimensional space. I was getting some pretty exciting results, but processing time became the real issue. I managed to compress a three-dimensional scan of a ball data that was fourteen meg, down to three nibbles!’

Lauren almost laughed.

‘What the hell is a nibble?’ Shaun asked. 

‘Well, there’s eight bits to a byte right?’ 


‘Well a nibble is half a byte. Four bits!’

‘So why not say ‘a byte and a half’ instead of three nibbles?’ 

‘Not as funny.’

‘I see,’ Shaun said, smiling.


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