There’s little chance you’re gonna get a 5 minute AVI at emailable size that looks good. The best compressors for good quality vs file size are, as you have found, MPEG4 or a QT file with H.264 codec. At good quality it is still going to be a considerable (but not massive) filesize. Have you tried dropping the framrate (30fps to 15fps?) usually this is an accepatble and viewable drop, and can considerably reduce your filesize.
You can encode an AVI using the mpeg4 codec (I’ve not done it on a Mac), but essentially that’s an MPEG4 file. I’m guessing if that was an option, you wouldn’t have had to encode the MPEG4 back to AVI.
Why AVI? If it is for viewing purposes only, surely other formats will be OK? Is it for mass distribution, or for client’s eyes only? If you establish what the target playback device is, you may find that you will have other alternatives.
Email is always problematic when you are sending video, simply due to size. I prefer to ftp files up to my website, and email a link for my clients to view.
Hope this helps!
Enzo Tedeschi
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Editor
Sydney, Australia