Avi in smaller size

[bloodsachok]

Im having this problem.
I hv this batch of avi(Jap anime) which have the same amount of time around 20mins.
Can someone explain to me why they are of different sizes??
They are all encoded with divx fast motion.
They ranged from 100mb to 190mb.
I have searched the forums and guides but none concerning avi size.
Also, which codec can be used to make avi in small size and in good quality.
Also, why do converting avi to mpg makes the video darker?
Is mpg/mpeg smaller in file size than avi which have the same amount of time?
I know there are a lot of questions here but i need to know.
Reply the link/links if there is a guide on this.
Or just answer here..
Im quite sure other reader would like to know too.
Thanks to anyone who bothered to read this and help me.

[Krispy Kritter]

File size can vary by codec used, resolution, bit rate, or audio type.

There isn't any one codec that is better than the others. Most of the avi codecs are very similar. The latest would be xvid.

mpg files are always larger, much larger than avi

[Abond]

filesize=runingtime x bitrate
If runing time is equal and the filesize is different, this is due to differences in bitrate.
Saying this you can imagine that an avi and a mpeg which have the same runing time can differ in filesize due to the differences in the bitrate. If the bitrate and runing time is equal then the file size is the same. So mpeg can be bigger, equal or smaller in size than an avi with the same runing time.

[ZippyP.]

File size can vary by codec used, resolution, bit rate, or audio type.

There isn't any one codec that is better than the others. Most of the avi codecs are very similar. The latest would be xvid.

mpg files are always larger, much larger than avi

Just a few misconceptions in the above.

To reiterate what Abond said, the only thing that sets the file size is the running time and the bitrate. If the running time is the same and the sizes are different, then the bitrates must be different.

Some video codecs are better at keeping quality at reduced bitrates, meaning that the sizes can be smaller. Mpeg for instance needs a much higher bitrate than Divx or Xvid to keep similar quality. That does not mean that an mpeg cannot be smaller, it can, it just won't look as good.

An avi can be made using a wide variety of codecs - DV,Divx, huffyuv, etc. Codecs found in avi files being shared on the web are usually pretty similar as they are going for max compression and quality is secondary.

[bloodsachok]

Thanks u guys..
That really help me to understand a lot better.
Just wondered why i nvr came across similar topic.
Im gonna look ard on editing mainly the bitrates.
Maybe post another forum.. hehe..
Thanks u all.