Bandwidth issues

[PrismUser]

Hi! I have just signed up after downloading the Switch Sound Converter. Before I go mad converting every file in sight, I wondered if any savvy users could advise me which format is best for up and down-loading to my own web site (not a blog or Facebook)? I need to create smaller files to the .avi that were shot on a Nikon camera. I also hope this will show an image and not an icon in thumbnail listings (Windows XP)

 

I need small file sizes because bandwidth is an issue, in addition to slllloooowwww modem times! I usually work with speakers OFF so have never taken much notice of sound issues in the past, but notice that not all files are supported on PCs. Is it reasonable to expect all users to be able to view any/all file types? I suppose I am asking is there an "industry norm" most people will be able to access no matter what browser or standard programmes they use? Thanks