Security camera footage in discovery loves to arrive as .dav, .264, or a folder with its own crusty player from 2009. Windows won't play it, VLC might not either, and your hearing isn't moving.
DVR makers wrap ordinary video in their own container formats so footage plays in THEIR software. A .dav file is usually Dahua's wrapper, .264 is a raw stream from any of a dozen brands, and the bundled player .exe is often the only thing that officially opens them, if it runs at all on a modern machine.
VLC (free) opens some .dav and .264 files: drag the file onto it and hope. If the DVR export included a player like SmartPlayer or vMEyeSuper, try it on a Windows machine with antivirus warnings acknowledged. If the video plays but scrubbing is broken, that's normal for these wrappers.
If audio matters, listen closely: many DVR exports carry audio tracks that only the original player will decode.
These wrappers can be converted into standard .mp4 files that play anywhere, keep the original timestamps, and scrub properly. We do this routinely, including the stubborn ones that need the vendor codec. Originals are hashed at intake and never touched; you get back watchable video plus the documentation that ties it to the file the State produced.
Hearing on Thursday and the video won't open? That's the use case.
File conversion, $50 with any order