The final size of your output file will be determined by the length of the source file and your output settings. To reduce the file size, load the file into the product, then click on the Target button, and choose a lower resolution like SD under Video.
If you wish to have an even smaller output size, click the Edit button and select Small Size on the pop-up window or Custom to customize it.
Note: If you set the output parameters to low it will reduce the output quality.