Firmware

DH_IPC-HX5X3X-Rhea_Eng_P_Stream3_V2.622.0000000.31.R.180813.bin

Dahua firmware released Aug 13, 2018. May work with 309 devices, including IPC-EB5531, IPC-EB5531-AS, IPC-EB5531-M.

Download

Permanent copy on the Internet Archive (item page)

Hardware IDs this firmware's installer accepts (309 devices).

Where these IDs come from

Install: the installer's device list (board families), 5 IDs, vendor General (not counted: a more specific list exists)
check.img: the device's own hardware check list, 309 IDs

Read from inside the firmware (dahua package (zip variant)).

Flash layout: 16 partitions, 10 written by this firmware

From the firmware's partition table (partitionV2.txt).

Partition	Start	End	Size	Image	Filesystem	Built
MinBoot	0x0	0x40000	256.0 KB	dhboot-min.bin.img	—	2018-08-13
U-Boot	0x80000	0xc0000	256.0 KB	dhboot.bin.img	—	2018-08-13
hwid	0xc0000	0xe0000	128.0 KB	not written	—	—
partition(ro)	0xe0000	0xf0000	64.0 KB	partition-x.cramfs.img	cramfs	2018-08-13
user(ro)	0xf0000	0x1000000	15.1 MB	user-x.squashfs.img	squashfs	2018-08-13
half-boot	0x1000000	0x1040000	256.0 KB	dhboot-min-halfstart.bin.img	—	2018-08-13
Kernel	0x1040000	0x1200000	1.8 MB	kernel.img	—	2018-08-13
web(ro)	0x1200000	0x1880000	6.5 MB	web-x.squashfs.img	squashfs	2018-08-13
product(ro)	0x1880000	0x18a0000	128.0 KB	pd-x.squashfs.img	squashfs	2018-08-13
custom(ro)	0x18a0000	0x1970000	832.0 KB	custom-x.squashfs.img	squashfs	2018-08-13
data	0x1970000	0x1a70000	1.0 MB	not written	jffs2	—
updateflag	0x1a70000	0x1aa0000	192.0 KB	not written	—	—
config	0x1aa0000	0x1b10000	448.0 KB	not written	jffs2	—
backup	0x1b10000	0x1b80000	448.0 KB	not written	jffs2	—
romfs(ro)	0x1b80000	0x1fd0000	4.3 MB	romfs-x.squashfs.img	squashfs	2018-08-13
dgs	0x1fd0000	0x2000000	192.0 KB	not written	—	—

Other files for much of the same hardware, from any vendor.