Depending on the specific brand or board model, you can often find the necessary files here:
If your device is a Zosi or Zosi-compatible model, they provide several rootfs-hi3520d upgrade files, such as for the ZR04GM or ZR04GA . Download Firmware DVR 5004XVR HI3520D Backup rar
Sites like GSM-Forum or specialized CCTV forums often host .rar or .bin backup files uploaded by community members. 3. How to Update via USB Depending on the specific brand or board model,