Step 1 Add files :

Press Add File Button to add source video files.

Step 2. Merge ( Press Merge Button to make futher settings):

Step 2.1 Select Direct Stream Clone as the Merging Mode:

In this condition, Direct Stream Clone mode will merge file with a super high speed and keeps the output video quality the same with the source file's.

Step 2.2 Press OK to further configue output format:

Press Advance Button to further costumize output settings as you like:

Step 2.3 After pressing OK, select an output folder as you like.

Step 3. Merging finished. Open output file.