I'm a big fan of H.264 as a download codec. Have you tried that? I usually mix down to 44.1Hz mono on my audio. You can also bump the frame rate down to half of the source frame rate. So, if it's 1080 60i, you can go to 15fps and if you shot 24p, you can go down to 12fps. Also, play with your keyframes. If there is allot of action and movement in the frame your kind of stuck, but if it's fairly static, you can bump your keyframes up . What's your frame size? You can save allot of bandwidth here to.
Daniel Wharmby
OMG Media Group
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Compressionista