Can I reduce space required when using Record Slideshow?

Hello.

I tried to play a bit with Record Slideshow functionality and it works well.

However, there is one big problem from my point of view in my case: presentation with 17 slides weights only 4.3MB without sound. When I add sound with Record Slideshow, file grows to 66MB as I speak for 32 minutes overs those 17 slides. Exporting to QuickTime movie is even more heavy as I end up with a file of 232MB!

Is there a way to force Keynote to lower audio quality? My audio MIDI input for the microphone is set to 16 bits (the lowest possible)... so I don't know where else to look in order to end up with a smaller file than 66MB as Keynote don't look to offer options in that respect...

Thanks for your input.

T