I have a split screen near the end of the video I would like to stretch left side across the whole screen, while its playing ,how do I do it
You need to use the Size/Position/Rotate (SPR) filter and keyframe the size at the beginning to be half the screen and at the end to be the whole screen.
I just happened to have the screen opened to that…
Add Size, Position, Rotate to your clip, and adjust the size, position, etc…
Now make it Keyframed by clicking the stopwatch icon
You get this Keyframe display, with one Keyframe set…
Move your Playhead.
Click the stopwatch icon to set a new Keyframe.
…and now at the new Keyframe, drag your image to its final size and position.
A smooth expansion.
(If you already knew the basics, please excuse the “patronizing”; someone else will get here on a search, and they won’t know yet.)