For files without an extension name, or some proprietary format of files that any common software cannot read/write, if you're sure it's a media file, then you can try using MediaInfo to detect its file metadata first. Alternatively, you can also direct use FileAnalysis to analyze its file type, thus determine that what software generated, encapsulated or encrypted this file.

As is known to all, malicious software or trojan virus usually modifies or damages the registry of system, which could lead to Windows errors when opening some files or programs, i.e. file type associations have mistakes. But it can be restored in some ways.