Introduction 

This article will go over how to change between various bitrate configurations and their effect on the dataset captured. The higher the bitrate the better the image quality however more memory is required to store said image. 

Requirement

• Maivin 2 
• BSP: Main build 58 

How to change between bitrates

1. The user is able to choose between (Difference detailed below):

   [auto, 5MBPS, 25MBPS, 50 MBPS and 100MBPS]

2. Once the user has selected the desired bit rate ssh into the Maivin.
3. Now update the camera config file as follows:

   sudo vi /etc/default/camera 

4. Navigate all the way down to H264_BITRATE and make the necessary change for e.g. H264_BITRATE = mbps50 
   

   ......
   # Controls the H.264 streaming compression level. The higher the bitrate the
   # better the quality of the image. The actual bitrate remains variable based
   # on the scene but the value sets the cap.
   # Possible values: auto, mbps5, mbps25, mbps50, mbps100
   H264_BITRATE = "DESIRED_BITRATE"
   ......

5. Once the bitrate has been updated, restart the camera service for the changes to take effect 

   sudo systemctl restart camera

6. Now the bitrate of the H264 stream should be updated, and the user should be able to record the dataset using the recorder.

Comparison between different bitrates 

The size of the files at different bit rate were calculated by running camera in H264 mode and each recording was 10s long:

Comparing AUTO with 100MBPS, the tradeoff between quality and size comes out to be about 5.8x.

Furthermore, the reason you don’t see a linear jump in file size between 50MBPS and 100MBPS is because even when set to 100MBPS it is only able to run at a maximum of 62MBPS. After viewing the JPEG and 100MBPS side by side, they seem to be very similar; however, the JPEG does seem to be a touch bit more saturated.

Driving Test Results 

This test was conducted in the Au-Zone office parking lot where the Maivin was mounted on the car about 78.7cm above the ground and driving at car at 5-6Km/h. The car was driven over a manhole cover which had text and drawing on it and the image at different bitrates were compared. 

100 MBPS

5 MBPS

25 MBPS

50 MBPS

AUTO

If the user is not concerned with the file size and would like the best quality image, going with 100 MBPS would be the best option.