Ok probably a lot of people know this but I have seen to many jumpy pause then slow motion clips today.
SO here is how to keep slow motion or fast motion going without holding down the Trigger forever.
It is very simple.
1.Press left or right TRIGGER to the speed you want it to go. (DEPENDS ON CONTROLLER LAYOUT DEFAULT IS RIGHT TRIGGER)
2.Press BACK or START button.
3.Let go of the TRIGGER.
4.Press BACK or START again.
NOTE: If you pressed START when you have done the steps above hit A to play the clip It should be in whichever speed you wanted.
I am sorry if there are easier ways to do this because I have not found them.
ALSO I did find this out myself when the game first came out though I have not posted it. I am sure others have found this so I do not take credit for first find of course lol.

I hope it helps.

ANOTHER TIP: If you want smooth slow motion but not constant in theater mode change your layout to digital your left trigger will then control slow motion and right will be fast motion. ALSO BADBOT Layout is helpful too it makes Dpad control motion by decreasing/increasing your playback speed by .2x.