Why is my slow motion clip playing back at full speed?
Slow motion clips (those shot at 120fps and 240fps) have 4 to 8 times the number of frames as a normal clip shot at 30 frames per second (fps). This allows you to play back the clip in slow motion and not duplicate any frames for the sake of the slow motion.
When you first import a slow motion clip, LumaClip will play the clip at 100% speed (@ 30fps) and will use only the frames necessary to do so. However, all of your original 240 or 120 frames are maintained in order to allow you to adjust the speed slower without duplicating frames.
For example, if you import a 240fps slow motion clip it will initially play back 30 of those 240 frames per second in order to play at 100% speed. However, when you open the LumaClip speed control you will notice that there is an indicator on the slider that marks the slowest speed you can choose without duplicating any frames. If you shot at 240, the slowest optimum speed is 1/8 (assuming your final export will be 30fps).
You can choose any speed above 1/8 and not have to duplicate frames. But keep in mind that if you shoot at 240fps and export at 60fps, then 1/4 speed is the slowest you can go before duplicating frames for the sake of the slow motion.