Whats the SoC?

Some of the more modern SoC's can do recovery via USB boot.
If not, you'll need an SPI flasher or similar to rewrite the uboot directly onto the flash, eg with a BusPirate or dedicated device.

I downloaded the rar file, unpacked and took a cursory look at the bin file.

Looks like its possibly encrypted or compressed post header, as I don't see many FF's or 00 strings in the file after the initial header.
strings also doesn't show any readable text, which ties in with it being compressed or encrypted.

A scan with binwalk ( http://binwalk.googlecode.com ) to see if it finds any recognizable FS or compression in there shows nothing.

I'm guessing its probably encrypted with some custom method.

You'd need more firmware files to look at in order to proceed.

Updated forum software to 2.0.14, changed default template to the traditional default, as I need to work on the old template to make it compatible.

Added some boards for the XiaoMi camera range, as I have some, and will probably fiddle with them!

Basic's -

root / ismart12

3rd Party Hacks -
https://github.com/samtap/fang-hacks

SDK (340mb)
1.5 version https://pan.baidu.com/share/link?uk=3981671631&shareid=2974078675#list/path=%2F

Full older version, including docs (3.4G)
https://pan.baidu.com/share/link?uk=1779995674&shareid=2611018017#list/path=%2F%5BSONIX%5D%2FSN986x_SBE&parentPath=%2F%5BSONIX%5D

Not an error,  you're in the bootloader - u-boot.
You need to boot past that into the OS.

First off, you'll need to see what it is internally.

I'd start off with trying to find more info.
Common tools I would use for this are

head  filename.ov | hexdump -C
file filename.ov
strings filename.ov

OSX, Linux have those built in. Windows 10 now has bash/ Ubuntu if you enable it so will have after a bit of work. 
Otherwise a linux live ISO will be fine too.

For dev work, you really want a Mac or Linux box (I'm biased after using Windows for many years and hating it, hehe)

As an example -

head configs.zip | hexdump -C
00000000  50 4b 03 04 0a 00 00 00  00 00 30 0f 91 4a 00 00  |PK........0..J..|
00000010  00 00 00 00 00 00 00 00  00 00 08 00 10 00 63 6f  |..............co|
00000020  6e 66 69 67 73 2f 55 58  0c 00 d6 b0 f3 58 8c b0  |nfigs/UX.....X..|
00000030  f3 58 f5 01 14 00 50 4b  03 04 14 00 08 00 08 00  |.X....PK........|
00000040  56 0f 91 4a 00 00 00 00  00 00 00 00 00 00 00 00  |V..J............|
00000050  11 00 10 00 63 6f 6e 66  69 67 73 2f 2e 44 53 5f  |....configs/.DS_|
00000060  53 74 6f 72 65 55 58 0c  00 d3 b0 f3 58 d3 b0 f3  |StoreUX.....X...|
00000070  58 f5 01 14 00 ed 98 c1  6a c2 40 10 86 ff 89 39  |X.......j.@....9|
00000080  04 0a 65 8f 3d ee 13 48  b5 82 7a 5b 42 7c 82 be  |..e.=..H..z[B|..|
00000090  40 69 3d 0a 1e a4 f7 9c  7c ae 3e 9a 1b e6 b7 0a  |@i=.....|.>.....|
000000a0  31 62 4f 96 f6 ff 60 f8  20 99 99 24 97 dd 9d 00  |1bO...`. ..$....|


You'll see that my file starts with PK, so mine is a zip file (as phil katz invented zip, so zip files use his PK header, more history on that here  - https://en.wikipedia.org/wiki/Phil_Katz).

file will also tell me that though -
 
file configs.zip
configs.zip: Zip archive data, at least v1.0 to extract

For your OV file, you'll need to look at the header, and see if its a standard format, or its a custom format.
Its more likely to be a custom format.  Typically those will have a header with where bits are in the file, and filesize, and maybe crc's.
If you're really unlucky, its also sha1 or similar encryption on the file data.

I've written about decoding custom format files before on here, look through some of my posts on that, or on my http://www.computersolutions.cn/blog under firmware ( http://www.computersolutions.cn/blog/?s=firmware )

If you post the output from  head yourovfile.ov | hexdump -C here I can take a cursory look and tell you which its likely to be.

Not really (opennvr firmware)

What you'll need to do is get hold of the SDK for the chipset, so that you can compile a kernel and app's.
Once you have that, then you can start building firmware and flash.

Issues are that not all hardware is identical, so you will have different NAND types, flash sizes, gpio usage etc.
Not insurmountable, but you'll generally want to pick the same hardware to develop, and port to.

The SDK for the HI3615C is here - http://pan.baidu.com/s/1o8TWZ0Y----

Let me know if you have problems downloading, I can put elsewhere.

Generally speaking, you'll want to open up whatever hardware you have.  Add serial headers, and connect up serial for minimal debugging, and for more serious stuff JTAG.  Boot up the hardware, and see what it tells you.  Hopefully you'll be able to see a boot log and bootloader, and communicate with it.

Developing with just serial is viable though if the hardware isn't too locked.
i.e. hopefully the device will have an accessible bootloader, then you can flash kernels and filesystems without too many headaches.

The flash will generally contain a bootloader (don't overwrite this, otherwise you'll need to use an SPI flasher or similar to rewrite).
The bootloader will load a kernel from the flash into ram, then execute it.
The kernel will then mount a filesystem from flash, and run the OS + programs.

A BSP or SDK allows you to build a kernel and programs (BSP = board support package.  SDK = software development kit).

Thats a brief overview.