I just figured out a way to convert video to m4r iPhone ringtone using Free Video Converter App. Let me share it below:
How to Convert Video to iPhone Ringtone For Free
1. Download and install Video Converter Free App onto your PC.
2. Launch the app. Click the Add Video button in the interface of the app to load video from your computer.
3. Play the video in the preview window. While playing, click the Start to trim and Stop to trim scissors to clip the video length. Learn more about how to trim video length.
Note: You need to set the duration equal to or shorter than 30 seconds for use as your iPhone ringtone.
4. Extend the Profile menu, select General Audio from the category, and then select M4A - MPEG-4 Audio (*.m4a) as the output format.
5. Click the Start Encode button to start to convert the video clip to m4a audio file.
6. Click the Folder button in the interface of the app to locate the generated m4a file in your PC.
7. Rename the file extension from m4a to m4r.
8. Launch iTunes and drag and drop the m4r file into iTunes library. The m4r file will go to the Tones section. You can now sync it to your iPhone and set it as your iPhone ringtone.