Drones and Dashcam Viewer

Using Dashcam Viewer with your DJI Drone Videos

Update May 20, 2018: The SRT-reading capability of Dashcam Viewer has been removed. Instead we will incorporate it into a new, Dashcam-Viewer-like, product specifically for drones called DroneViewer. DroneViewer will be released soon. In the mean time, you can continue to use v2.7.8 of Dashcam Viewer to process video with SRT data.

As you might guess, the video and GPS systems on commercial drones (UAVs) are very similar to the systems found on your everyday dashboard camera. Both record video and have GPS receivers that capture time, position, and speed. So it wasn’t much of a stretch to add drone support to Dashcam Viewer, at least for some of the more common drone models on the market.

The combination of Dashcam Viewer and drones makes for a powerful duo. With Dashcam Viewer you can see exactly where your drone was on a Google Map at the time of video capture. You can GeoTag key points in your video to mark their positions on the Map and return to those points at any time. The GeoTags also display the line-of-sight (LOS) distance from the tag to the current drone position. This can be used to show your distance from the operator, as shown below:

GeoTags, shown in the Map and in GeoTags list on right, show key points of interest and distances to the UAV. The graph in the bottom-right shows the UAV speed versus time. The lower-left Dashboard display shows the speed distance, heading, position, and number of GNSS satellites in view. The LOS distance of the drone from the operator was 1.2 miles at this point in the video.

You can then export your GeoTags to an Excel file for review and analysis. Below are two more examples showing Dashcam Viewer used for post-flight examination of drone video.

Dashcam Viewer after loading a movie and SRT file from a DJI Mavic Pro. Geotags were used to mark the position of two offshore oil platforms that didn’t appear on the Google Map.

Dashcam Viewer being used to survey an oil field for leaks. The video was captured using a GoPro Hero 3 Pro mounted to a DJI Phantom 2. The GPS data was recorded using a FlyTrex Core 2.

Currently Dashcam Viewer can accept GPS data from drone footage in two forms: SRT file and FlyTrex Core 2 file. Both these methods apply to certain DJI drones and are described below.

Importing drone flight data from a DJI SRT file

If your DJI drone is controlled by the DJI Go 4 App (used to fly the Mavic Pro, Phantom 4, and Inspire), then you can easily import your flight trajectory into Dashcam Viewer via the SRT file. Before your flight, be sure you turn on the Video Caption option in the Go App camera settings.

Turn on “Video Caption” in your DJI Go App settings to have your UAV create SRT files alongside your movie files

This will make the drone create an SRT file for each movie. The SRT file contains the flight trajectory information. Make sure the SRT file is in the same directory as your movie and has the same root name. Drag one of your movies into the Dashcam Viewer window or select Open Movie File from the File menu. Dashcam Viewer will process the data just like it does with a dash cam and you’ll see your drones flight path and current position as the movie plays. The speed and number of satellites in view are also shown in the Graphs.

A few caveats when working with SRT files:

  • If you rename the movie, be sure to rename the SRT file as well or else Dashcam Viewer will not be able to find it.
  • The speed of the drone is computed based on waypoints. While it’s great that DJI conveniently logs the drone’s flight data into an SRT file, the speed of the drone is not recorded to the file and the latitude and longitude are not stored in high precision. Dashcam Viewer uses the time-stamped lat/lon values to estimate the speed. The lack of precision means the drone speed and direction can be inaccurate and appear to vary wildly. Dashcam Viewer applies a smoothing function to dampen the speed variations. While this helps, it’s not a perfect solution. Ideally, DJI would modify their SRT file data to include native drone speed and higher-precision latitude and longitude. (There are other ways to extract the flight data to higher-precision but they are not as convenient as the SRT file method).
  • High resolution videos (>1080p) or high frame rate videos (>30 fps) may stutter when played in Dashcam Viewer.

Importing drone flight data from a FlyTrex Core 2 CSV file

FlyTrex provides simple add-on logger that records your drone’s flight data to a microSD card. The Core 2 is compatible with many drones but I have only tested this method with the DJI Phantom 2.

  • After your flight, upload your FlyTrex Core 2 data file to the FlyTrex website. Click on the arrow at the top right of the mission and select Export Mission.
  • Choose the Download CSV option to export your flight data.
  • Find the CSV file and drop it in the same folder as your flight movie. Rename the CSV file so it has the same base name as the movie file. For example, if your movie is called oil_pipeline.mov name the CSV file oil_pipeline.csv.
  • When you load the movie into Dashcam Viewer the GPS flight data will be loaded as well. Unlike the SRT method, you will need to adjust the synchronization of the GPS log to the video. This is due to the difference in time between when the video recording started and when the GPS log started. To override Dashcam Viewer’s automatic syncing feature, go into the Preferences and de-select the Always Auto-Fix Time Offset checkbox.

  • Close the Preferences window and click on the Graph window. Now you can use the ‘m’ and ‘/’ keys to make coarse adjustments in the time-cursor position. Each click moves the cursor forward or  back 10 seconds relative to the video. Use the ‘,’ or ‘.’ keys for fine (1-second) adjustments. Look for key points in the movie, such as take-off or landing, to insure good synchronization.

  • When you are happy with the synchronization, click the Save Settings button, which looks like a disk icon.

  • The icon will turn green to indicate the settings, including the synchronization, have been saved. A settings file will be created in the same directory as the movie file. This file is automatically loaded every time you load this movie. If you’re not happy with the synchronization, click the disk icon again to delete the settings file. Then you can try again.

And finally here’s an example of what you can do with drone video in Dashcam Viewer.