====== req_vid ======
**C → S → C {type: 'req_vid', from:..., maxBitrate:..., maxFramerate:..., scaleDown:...}**

req_vid – ask other end of call to change its transmitted video stream's bandwidth or quality.

===== Arguments =====
  * from - address of client sending the command
  * maxBitrate - (optional) maximum video bandwidth, in kbps
  * maxFramerate - (optional) maximum frames per second
  * scaleDown - (optional) video frame size downscale factor