DV Info Net - Basics on video codecs and formats

look at video as plain data. Lots of data.
so to store or transport it, you need to compress.
The bad thing with video is it is sequential data. It means that you need to receive in the same order that it has been sent, so timing has its importance.

That is why in modern codecs , you got a clock concept embedded. If you loose some data, you do not really need to know how much you loose, but how long.

Basically some codecs still respect the old concept of pictures and frame and treat each picture or frame separately They are called Intraframe codec. These are codecs for recording or storage, giving nice result but require huge space.
DV, MJPEG, JPEG2000, some type of MPEG2 or MPEG4 are in this league.

The other part of codecs are streaming codecs. They consider video as stream of data.
This include most codec used for transport from the satellite to your TV for example.
They are made to be very resistant to data loss or corruption and highly compressing data.
HDV (a form of MPEG2-TS, TS standing for Transport Stream), Most of MPEG4 codec.
So they usually compress pictures by packets (or group called GOP, for Group Of Picture)
in a packet, you got usually one reference picture that is fully encoded, the other pictures being only expressed by their difference with the reference picture.

The fact is that most current MPEGx codecs are highly configurable so you can turn a transport codec that was designed to send video across the air into a recording codec embedded into a camera.
You just need to tweak some parameters to totally change it.

the main parameters to consider are
Bandwith: the amount of data per second that is delivered.
Picture compression: if it is Intraframe or GOP based, and if GOP based you need to know the GOP structure.(length and type of frames)
a GOP usually starts with a complete picture (the I frame), then is followed by by some other type of frame (B, P), but Wikipedia has a nice page about that.
Group of pictures - Wikipedia, the free encyclopedia
Number of bit used to represent data (usually 8 or 10)
Color reduction : A full signal is defined as 4:4:4 for the three parameter Y:U:V (Y luminance, U V color coding)
Most of codec are going to code 4:2:0 meaning that you got a black/white image at full resolution ,while colors are coded on 1/4 resolution. The eye is weak enough on dealing with color to be fooled by such trick. Professional codec are usually going to 4:2:2.

10 years ago, we got intraframe only codec in 4:2:2 and we were struggling with huge data file and bandwith difficult to handle by our slow processor. Capture has to be done in real time. At this time it was not data transfer , but more acquisition of an analog signal into a digital form.
Then we got DV that makes us jump into digital video, but we also downgraded from 4:2:2 to 4:2:0 (for european) or 4:1:1. Files were still huge, but since it was digital, there was no loss in the transfer, and expensive capture card was reduced to a simple high speed serial port (firewire).
In the same time, VHS was replaced by DVD and Mpeg2 start to rule.
Unfortunately, our processor were far too slow to encode Mpeg2 in realtime, so converting DV to mpeg2 was a very long process.
Today, Mpeg2 still rules for DVD and even Blu-ray, DV is slowly disappearing. Not because it was bad, but simply because it was designed to be stored on tape.
Most camera you can find now are storing video on some form of digital memory like memory cards or hard disk. There is no more capture, but file transfer at very high speed.
today you can transfer one hour of video in 10 minutes.
At the same time we got digital storage, we see Mpeg4 replacing Mpeg2 , DV and HDV (a form of Mpeg2 that was used to extend the life of tape on camera, bringing high resolution.)
Today, most of proprietary codecs developped by big names (Microsoft , Apple, Adobe, Canon, JVC, SONY) are using some type of Mpeg4.