Frames per second describes how often the video supplies a new picture. Hertz describes how often the display refreshes. A 120Hz screen does not make a 24 fps film contain 120 original pictures each second; the television must repeat or process the available frames.
Follow the two clocks
The source timeline and display output need a sensible relationship. A 24 fps film can fit evenly into a 120Hz refresh by showing each frame five times. Other combinations may require uneven repetition or a change in output timing, which can be noticeable during slow camera movement.
Understand added motion processing
Some televisions create intermediate images to make movement appear smoother. That is different from showing more original camera frames. Interpolation can change a film’s appearance and produce artefacts around moving objects, so a high refresh specification does not tell you whether processing is enabled or desirable.
Compare motion on familiar material
Use a slow pan for film and fast lateral movement for sport. Check the player’s output timing as well as the television’s motion controls. Change one setting at a time and keep a note of the original. A stable frame rate with modest processing is often easier to evaluate than several automatic modes acting together.