Codec, codec and more codecs!

[gtrasi]

Hi all

I need a refresher on all codec stuff. I know that codec stands for "compression/decomp" and wht it does is reduce the size of mpeg file(video/audio) by compressing it.

But wher does the file format com into picture..lik real video or Divx.
Also wht format is .dat?

And is .avi a file format or a codec or both?

Are all video/audio file in mpeg?

[RJ]

wht it does is reduce the size of mpeg file(video/audio) by compressing it

No. It reduces the size of a video file, no matter whether it is mpeg or not. mpeg itself is a codec, too. Actually, there's 3 different mpegs: mpeg 1, 2 and 4.

But wher does the file format com into picture..lik real video or Divx.

DivX is a video codec. There is also a .divx file type, but that is a container format.

Also wht format is .dat?

VCD. It's actually only an MPEG-1 file with modified header.

And is .avi a file format or a codec or both?

It's no codec, it is a container format. A file type that holds video, audio etc. files in it. That way you have a single file with video and audio, and both are in sync. It is possible to extract (demultiplex) the single audio and video files if you need them.

Are all video/audio file in mpeg?

Well, the .mpeg file is a container file for mpeg video and audio. If you have only the video, there is no need for a container file, but it is possible to just put the video file in that container.
So, an mpeg file can have video only. But usually they'll have audio as well.

RJ

[gtrasi]

Thanks but I hav som more questions...

If mpeg is a codec then it has to compress some data..what format will that data be in?

I used to thnk that all movies to be played on the PC will hav to be mpeg uncomprssed files whch are later comprsessd by codecs such as Divx, .avi etc

But u said that avi is only a format..then if I hav a video in .avi is it uncompressed ...doesnt need a codec to play it?
But earlier, WMP7/8 couldnt play .avi files..used to say need to dwld codec from the net...(so i got Divx player whch played .avi files really well)
Now WMP9/10 does play it though.

[RJ]

If mpeg is a codec then it has to compress some data..what format will that data be in?

Ok, my expression wasn't really accurate, sorry for that. MPEG is a video format, it defines the way a video can be compressed. You can use an MPEG codec to actually encode footage into the MPEG format, and decode them for viewing.
So, when you encode footage using the MPEG-2 codec, the result will be in the MPEG-2 format.

I used to thnk that all movies to be played on the PC will hav to be mpeg uncomprssed files whch are later comprsessd by codecs such as Divx, .avi etc

Then, you used to think wrong. MPEG it not uncompressed at all. It is in fact very highly compressed. It is compressed so much that it is not recommended to do video editing on an MPEG Stream (besides simple cutting, that is).
DivX is MPEG, too. It derived from the MPEG-4 format, which is newer than MPEG-2, and compresses a bit more without loosing quality.

then if I hav a video in .avi is it uncompressed

AVI is only a container format, it holds video and audio. The video and audio inside could be encoded by any codec out there. It can also be uncompressed, but it doesn't have to.

uncompressed ...doesnt need a codec to play it?

Nope. If you didn't compress it, you can't uncompress it.

But earlier, WMP7/8 couldnt play .avi files

That can't be. WMP plays AVI since the first version. What you meant was "couldn't play *some* AVI files".
In fact, you can play any AVI that holds a video you have the codec for.

RJ