There are a few keyboard shortcuts you can use in the Web App.
You can start and stop the video by pressing the spacebar.
While entering a comment, you can submit your comment by pressing Enter and the video will automatically resume.
J for backwards play, K for pause, L to playback single speed, double speed, quadruple speed.
If you want to jump ahead frame by frame while the clip is paused, you can use the left and right arrow keys.
If you are viewing a clip that has multiple version, press S and it will split the screen so you can compare versions.
Press I to show the metadata information.
Hold R during playback to define a cycle range to repeat.