DV4 videos are recorded by Bosch Security Systems closed-circuit television (CCTV) systems and there seems to be no way how to convert them to other formats, such as MPG, using some kind of 3rd party video conversion software.
The only way would be to use the software for Bosch Security Systems, called Bosch Video-over-IP (BVIP) Lite Suite, which allows users to export their .dv4 files as .mpg files.