unkown filesize, modrewrite issue

[maikon]

I have an issue that gives with unknown filesize
with rar, rmvb, mp4 and many other file exstensions
the only file exstension that gives eta and filesize is zip.
My sysadmin said this

"This is typically a result of gzip encoding being active in apache. The newer browser releases aren't interpreting it the same way, giving the unknown file size issue. I would suggest you to have a look into [webmasterworld.com...] for mod_rewrite rules to get around the problem."

but the thing is that i dont know what to look on that topic to bypass the issue

i have xcache installed

[maikon]

any help please