.DAT is not a format. It's a generic file extension that can mean anything at all that just stands for DATA. You have to understand the arrangement, or format if you will, of the bytes in the file. You need the documentation on the format of the file whatever device you have wrote. Without that, you're just guessing at what each byte means and have no way of converting it to any other format with any meaning.
You might want to try MediaInfo
] to see if you can get any information about what the actual format might be.
Truthfully, you should just use a conversion tool for this as converting the audio and video streams and keeping them in sync is not a trivial task.