Files with the extension DMX belong to the category of project files. What do DMX files contain? Contents of files with the extension DMX are projects created using an application named Source Filmmaker.
Files with the .MP4 extension contain audio and video streams encoded usually in the MPEG-4 format, but they are supported also by many other formats. It is a container – file, and it may also include metadata, subtitles or images, although it is rarely used for this purpose.
After converting the file to the new format, you will be able to use other programs to support it. Keep in mind, however, that the DMX file after converting to MP4 may differ slightly from the original. The most important information should be kept, but if you want the file after conversion from DMX to MP4 to be the same, you have to do this carefully and choose the proper application from the list below.
There is no guarantee, of course, that the conversion will come up to all your expectations, but it will certainly help you. If, after all, the effect of converting DMX to MP4 does not meet your expectations, you can simply try to find on the Internet a different version of your file in DMX format, properly converted to a MP4 file by someone else. If this fails, use the information provided in the further part of the website.
Unfortunately, if after performing the two previously described steps (trying to find your DMX file converted by someone else, and the attempt to convert it to MP4 on your own) you still have a problem with your file, then there are only a few solutions left. You can once again try to find and install an application that can open the DMX file in its original format (without conversion to MP4 file). Such a solution will be difficult to implement, but it certainly will give the best result.