Question on bit rate adaptation

Hi,

Can jitsi team explain how bitrate adaption works please?

I observed the following behaviours with one way screen sharing use case.

  1. Sharer A shares his screen with 10 frame per seconds on Mac, and he shares a vi editor (editing source code)

  2. Sharer leverages network link conditioner to set uplink bandwidth

  3. Two participants join the screen sharing from another Linux box, and the downlink bandwidth is about 30Mbps.

  4. When sharer A sets the upload bandwidth as 5 Mbps, and moves his mouse vertically in vi editor, the video on other two participants is very blurry and movement of the mouse is delayed. From the webrtc-internals on sharer chrome, the sending frame rate is 1 frame per second, and the bytesSent_in_bits is about 100K.

  5. When sharer A sets the upload bandwidth as 10Mbps, and moves his mouse vertically in vi editor, the video on other two participants is very clear, and the movement of the mouse is visible immediately. From webrtc-internals on sharer chrome, the sending frame rate is 10 frames per second, and the bytesSent_in_bits is about 2M.

I am curious to know why the difference between 10 Mbps and 5Mbps is so huge. I attached two screen shot of webrtc-internals for reference.

Many thanks,



/Kaiduan