40 minutes in 100 MB as SD will be 42KB/s, which is a very, very low bit-rate, though it is possible, if one looks at some of the TV episode sharing sites. They can get 42 minutes into files with sometimes less than 100MB (91MB), but the quality is terrible, even with a sophisticated codec like H.264.
40 minutes in 100MB as HD will look very, very terrible, even at 250MB.
Can you explain to your client, that such a wish will come at a very hefty price?
You could provide him/her with samples (1 minute video at the same bit-rate as 40 minutes would be at 100MB) via
MPEG Streamclip, as the Export as QuickTime (CMD+E) option gives you the option to set a bit rate, which in reverse will show you the target file size.
For example, I have transcoded an HD (1920 x 1056 pixel) clip via
MPEG Streamclip to four different ones, all using the same small data rate, thus a small clip (equivalent to 40 minutes in 100MB) should come out.
It didn't work with HD, only with SD. The HD clips were all 15 or 17 MB in size, with 1m25s of visual and fast moving content.
It looked horrible.
The source image
HD results and settings
SD results and settings
I applied the same settings in HandBrake, as you can set a target size and also selected the two pass method, but the results were horrible too.
I got a very good result with a target size of 25MB for the 1m25s video, which would be a combined data rate of 300KB/s for video and audio.