rtc_tools/rtp_generator/configs/vp9.json

{
  "video_streams": [
    {
      "duration_ms": 10000,
      "video_width": 640,
      "video_height": 480,
      "video_fps": 24,
      "rtp" : {
         "payload_name" : "VP9"
      }
    }
  ]
}