How to edit a Mini 0805 DVR firmware and have a custom video bitrate


A Mini 0805 dash cam is based on am Ambarella A7 processor and there is  the tool to easily modify firmware an have a custom bit rate settings. So you can modify it to suite your needs.

A bitrate edit is possible withthe  bitrate edit tool called  An Ambarella cross platform firmware editor. After opening the firmware file you are presented with a bitrate  table.

2016-05-10 18_48_30-Bitrate Editor 1.0.1

Columns :

  1. Bitrate – an average recording bitrate
  2. Range[min] – a minimal bitrate
  3. Range[max] –  a maximum bitrate
  4. Type – “3” stands for a variable bitrate. It means that a recording bitrate varies between min and max settings according to frames complexity and maintain selected average bitrate. It’s default, because allow to reduce a file size, and main a good quality.
    “1” – constant bitrate. The recording bitrate is constant. This option can be usefully if think that an Ambarella don’t optimally selects a current bitrate value for a variable bitrate.

This bitrate table have 159 rows, but not all of them are effective. After some playing with the bitrate table and the bitrate view program I have connected rows numbers with actual resolution quality settings from 0805 menu. Numbers from table represents rows numbers from bitrate table.

These are the bitrate values I’m using now.

2016-04-09 12_42_30-Bitrate Editor 1.0.3

I have only changed  values for 2560×1080 resolution.

The super fine quality have constant  24 Mbps rate and I’m using it daily, because my trips usually are short, so I do not have need to save micro SD card’s space.

The fine quality inherited default super fine(18 Mbps variable) bitrate for 2560×1080 resolution. The normal quality has 10 Mbps variable settings.

I do not say that these settings are optimal for 0805 camera. This is just demonstration for ability have custom bitrate.

I hope this information would be useful for you. And for ending this is instruction for updating camera with custom bitrate settings.

Basic bitrate edit flow:

  1. For hack you need Mini 0805 firmware file. I  recommend to download it from here. Alternatively you can backup existing firmware.
  2. Download firmware editor.
  3. Start editor and select to open Ambarella A7 firmware file.
    2016-05-10 18_22_23-Ambarella Firmware Toolbox 1.3.2
    2016-05-10 18_11_55-Load A7 firmware
    2016-05-10 18_12_05-Ambarella Firmware Toolbox 1.3.2
  4. Extract files from partition
    2016-05-10 18_40_59-Ambarella Firmware Toolbox 1.3.2
  5. Start bitrate editor
    2016-05-10 18_34_21-Ambarella Firmware Toolbox 1.3.2
  6. Select and open PRI.a7h file
    2016-05-10 18_36_34-Bitrate Editor 1.0.12016-05-10 18_39_13-Open
    You will see the bitrate table, that you can modify.
    2016-05-10 18_48_30-Bitrate Editor 1.0.1
  7. Change as you wish and apply changes
    2016-05-10 18_56_08-Bitrate Editor 1.0.1
  8. Update firmware
    2016-05-10 18_58_06-Ambarella Firmware Toolbox 1.3.2
  9. Firmware edit tool now will build new firmware and place it in directory of original firmware. New firmware file will be named “a7firmware.bin”
  10. Rename file to “firmware.bin”  and put it to the root directory of 0805 micro SD card.
  11. Turn on camera, it will ask to update firmware, agree. After update remove “firmware.bin”

Change a device firmware at your own risk.