How to stream the lowest possible latency video from a DJI drone

Intro

DJI Fly App is able to stream the video it is getting from a drone via RTMP protocol. We can stream from the app directly onto Youtube, but we can also stream to our PC where we can have more control over the stream.

Prerequisites

You will need:

• a DJI Avata drone and DJI Goggles 2 or similar
• a mobile device with a DJI Fly App (this can only be downloaded from the DJI web site, the app is not present in the Google Play store)
• an OTG USB Cable to plug into the Goggles and another USB-A-to-USB-C cable to plug the USB-A end into the OTG and USB-C end into into the device with the DJI Fly App
• A network-connected PC with the following software:
• VLC
• OBS
• MediaMTX
• Both your PC and your Mobile Device should ideally be on the same WiFi network

Stap 1 - Prepare for getting the video out of the DJI ecosystem

• Connect the Mobile Device with the DJI Fly App to your DJI Goggles, via the OTG USB Cable so you get the drone camera view in the DJI Fly App
• in a DJI Fly App once you are in the drone camera view
  • tap “…” menu in the top-right corner
  • tap “Transmission”
  • tap “Live Streaming Platforms”
  • tap “RTMP”
  • RTMP Address - here you will enter the address of your RTMP Server (later)
  • Stream Key - not necessary for us
  • Resolution - if we want low latency, set it to the lowest resolution - 720P
  • Bitrate - again, we want low latency, so we set this to “Smooth”
• If your googles can connect to the phone by both cable and WiFi, use the cable option for faster video transfer. DJI Goggles 2 support cable connection only

DJI Fly App only allows to stream via RTMP protocol, and the app acts as a client, so we will need to setup an RTMP protocol server. You can actually enter an address of a youtube RTMP protocol server here, for live streaming, but we’re working towards having that video stream on PC for further processing.

Step 2 - setting up the RTMP server on your PC computer machine

This can be done in many ways, even with ffmpeg oneliner, BUT most of these ways introduce unnecessary latency and we don’t like that. We will use the MediaMTX server, available from here:

• https://github.com/bluenviron/mediamtx
• https://github.com/bluenviron/mediamtx/releases/tag/v1.19.2

Download the release zip, extract it, and run the exe file. Now, check your PC’s IP address (Win+R, cmd, ipconfig) Your MediaMX RTMP server works on rtmp://YOUR_IP_HERE:1935, so if your IP is 192.168.1.10 your RTMP server will be at rtmp://192.168.1.10:1935

Step 3 - connecting the DJI Fly App to the server

We go back to the DJI Fly App “Camera View/…/Tranmission/Live Streaming Platforms/RTMP” window, as described in Step 1. We fill in the following options:

• RTMP Address: rtmp://192.168.1.10:1935/live/ (with ending slash)
• Stream Key: drone_video And we tap “Start Livestream” Now we can on our PC open this url in the browser to see the WebRTC stream http://localhost:8889/live/drone_video/

If everything works ok, you should see the feed from the drone in your browser tab.

Step 4 - measure the video latency

To measure the delay from the drone camera to our screen we do the following:

• Open https://www.mstimer.com/ on a half of your screen.
• Open the drone video feed on the other half.
• Point the drone at the mstimer.com website with the milliseconds counting.
• Ensure the picture is clearly visibel in the drone video feed.
• Take a screenshot.
• From a screenshot count the difference in millisecond between the time on mstimer.com website and the time on the drone feed In our case that delay

Addendum

Test https://github.com/genymobile/scrcpy as well.