Nikon D3300 Reference Manual page 185

3
Select Choose start/end point.
Press the P button, then highlight
Choose start/end point and press 2.
4
Choose the current frame as the new
start or end point.
To create a copy that begins from the
current frame, highlight Start point
and press J. The frames before the
current frame will be removed when
you save the copy.
To create a copy that ends at the current frame, highlight End
point and press J. The frames after the current frame will be
removed when you save the copy.
P button
Start point
End point
Recording and Viewing Movies 165