Under the hood, it runs a reference design by a company called Hisilicon (specifically the chipset). The firmware isn't magic; it’s a squashfs image packed with a boring, but functional, web server.
Your DVR has forgotten how to be a DVR. It’s suffering from digital amnesia. Dvr-104g-f1 Firmware Download
If you cannot find the exact "F1" revision, look for or Standalone H.264 4CH firmware. The "F1" usually indicates a specific flash memory chip (Spansion vs. Samsung). If you flash the wrong one, the unit will beep at you like a sad robot. If you flash the right one? It roars back to life. Under the hood, it runs a reference design