I've been noticing that sometimes, the thumbnail preview isn't enough for me to know which sample is in a particular slot. 2 examples are a black logo with an alpha background (all you see is what looks like an empty slot) and where you have two samples that look exactly the same on the first frame but go on to have other variations as the video plays. Being able to see the filename by hovering over the sample window for a couple of seconds would really help in these cases. I'm talking about something like the yellow tooltip notes you sometimes get in other programs.
