River Past Video Slice will automatically retrieve the duration of the input video. The conversion duration is set to the same as the input file duration when the video is opened.
Click on the time line. You will notice the cursor 
and preview window both change accordingly.
Now, click on 
"Set Start Time" button.
Click on the time line again, a little before the end this time.
Click on 
"Set End Time" button.
Move the cursor to the middle of the clip.
Click on 
"Split Video" button.
The above steps trim the beginning and the end of the video, and split the video into two.
