The steps to cut the music in the video into MP3 are as follows:

1. Download and open the Format Factory software on your computer, and click MP3 in the upper left corner.

2. Click the Add File button in the upper right corner.

3. Select the video you want from the computer folder and click Open below.

4. Click the OK button in the upper right corner.

5. Click Start above to start extracting the music from the video file.

6. Click the output folder in the upper left corner to save. At this point, the music in the video was successfully cut into MP3 and saved.