screen record frustrations

[alpinestars69]

i like the ability to screen record. it helps to shorten video clips with the parts that you don't want & creates a new clip that is really nice. my issues that happen when i do shorten clips are

the file ext. gets changed to something other then original. ( why would it need to do that why)
the pic thumbnail from original goes away. no more pic. thumbnail
the audio is missing.
when put in a playlist certain new shorter clips will not really play. clip starts long long pause & 2 sec. of play long pause, finally i hit next clip & it plays fine for 3 sec & then goes to next clip.
sometimes the screen recording will not play at all, it loads but nothing.

all i want to know is, if i have a 5 min video that is .mov & i just want 2 min of that video but i still want it to be .mov like the original video just a shorten version with the part i want not the part when the camera is on & the action has not happened yet.

[alpinestars69]

i would love a reply to this question that is helpful in correcting these issues