Strange video compression question

Hi, this is regarding using .mpg & .mpeg files in flash MX.

I have used video footage quite a few times, but everytime it seems to have a wierd effect.

I have created a .swf that uses some .mpg footage, offline it shows the file as 450k in size, when I upload it, it changes to 586k in size.

It has increased in size when I have uploaded other files containing video footage to the web also - why is this??

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