Use 16 bit color for screen recording and that will bring the file size down quite a bit. It also will allow your computer to work more efficiently! But let me explain first what “32-bit color” vs. “16-bit color” (and 24-bit color) really means! Then you may make your decision based upon what’s “really going on” under the hood!
16-bit video usually uses 5 bits (32 brightness levels) for red, 6 bits (64 brightness levels) for green (because our eye is more sensitive to green), and 5 bits again (32 brightness levels) for blue. So, 32 X 64 X 32 equals the famous “65,536 colors” you often hear about. Some Macs use 5 bits for each (for 32 X 32 X 32 = 32768 colors) and then uses 1 bit for an alpha channel. You most likely use the first type, however.
“32-bit color” is actually 24 bit color, plus an extra 8 bits for an “alpha” channel. Thus, 32-bit color is using 8 bits (256 brightness levels) for red, 8 bits (256 brightness levels) for blue and also 8 bits (256 brightness levels) for green’s brightness and 8 bits for the alpha channel, so it is actually 24-bit color with the added 8-bit alpha channel included. I understand that some video card’s transparency effects are dependent upon the 32 bit mode, as those 8 of the 32 bits that are being used to describe an “alpha” channel that describe the card’s levels of transparency. If you are not using transparency effects (and you shouldn’t be during recording, though the effects may be captured, but it is slowing everything down), then using the 32-bits is even more wasteful. You only need to see 256 levels of RGB when doing demanding graphic image manipulation in Photoshop or other image manipulation programs, and you generally do not even need to actually SEE that (only have the math being done at that resolution… big topic there… don’t get me started!) The 5-6-5-0 bit depths at 16-bit color are plenty adequate for general use.
I doubt that did anything but make the waters even more murky, but that is the truest answer I could give to you! 🙂