What does the Limit YUV for 5D do? And what are the differences between Low, Med and High? And what is the ProResHQ option for. Does it just use Apple ProRes422HQ, or does it use Cineform "innards" and output it ProRes? Thanks.

The Canon 5D records the "Y" channel of 8-bit YUV using the full 0-255 range. In video the normal range is 16-235, allowing for super whites and blacks. When you check the box, the Y is encoded to the smaller range, but at the higher bit resolution (64-940 at 10 bit), so there is no loss or stair stepping in the shading.

The low/med/high is the amount quality in the image, or the amount of compression. "Low" compresses the most, "High" the least. Since CineForm is not a constant bit rate codec, you need to do a conversion of your material at the different settings to see what works for you.

When ProRes is selected as the output, the we just use the standard ProResHQ encoder that ships with FCP.