How to convert .dsm files to .mp4 format.
Converting Digital Sound Modules directly to MPEG-4 Videos (.dsm to .mp4 conversion) should be possible, even though your options are somewhat limited. It relates to users attempting to encode DSM audio to MP4 video.
Try using media editing software or (online) conversion tools, such as the MediaCell Video Converter or AVCHD Converter, which should allow users to import DSM audio and export it in MP4 format.
A multimedia converter for OSx and Windows
A free software for MP4/3GP file conversions of portable video devices.