allow manual playback speed

[magland]

          > Got it. Okay the first link should be working properly now.

First link looks great! A minor wishlist request would be the ability to manually specify the 'video playback' speed (the slowest, 0.1x, maybe still goes too fast for microscopy data) and/or preload future chunks of the video to try to smooth the frame-by-frame rendering (this dataset should have been chunked pretty decently in this regard)

Originally posted by @CodyCBakerPhD in #205 (comment)