VideoReel - Why did short video become long when rendered?

In VideoReel, the length of the output video will depend on the length of the music track you selected/uploaded or the length of the Template, whichever is longer. For instance, if you have selected music that is of 30-second long while the Template runs only for about 10-second long, then the output video will be 30 seconds in length.

The "Loop" (number of times you want to repeat the video) may also affect the video length.