The file is apparently a recording from a Bosch DIVAR DVR-5000-16A000.
Specification claims that this system records "H.264, 16-channel Video, 4-channel Audio".

The user who uploaded the sample added the following text:
I am having the same issue with *.dxa files to any other format.  This is also a security video and ffmpeg will not convert it.  Can you please let me know what I am doing wrong?  This has always worked great for me on other files...

josh at edmundsonlawfirm.com