Automatic Video Synchronization

Benedikt, January 29 2021

For athletes and coaches, one of the most intuitive feedback tools is video analysis. Good videos show all details of an athlete's movement and help to raise his self-awareness. The feedback is visual and we are used to this as it's the same we see with our eyes.

However, video analysis is subjective and there are things like speed changes, friction forces, that a video cannot capture. Other information sources are needed. Wearable sensors are a natural choice. But they only provide abstract and difficult-to-interpret curves. Without any (visual) context it's very difficult to get the meaning of these curves.

Picture of filming athletes for a synchronized video.

Overlay data on videos

The solution to this problem is to overlay these "sensor curves" onto the videos. For many years there exist tools that allow you to do this. But these tool require that data manually aligned with videos, often based on specific synchronization movements. This is very work-intensive and impractical.

The solution

With our solution, data is instantly synchronized with videos and no synchronization movements are required. You can synchronize videos from any camera that has an audio/microphone input. This could be a handheld camera or even a GoPro with a microphone adapter.

Our video sync unit connected to a GoPro camera.
Our video sync unit connected to a standard handheld video camera.

How does it work?

The use of our video synchronization is extremely easy and straightforward:

  1. Switch on the sync unit.
  2. Leave it outside for about 20 minutes to guarantee perfect time synchronization.
  3. Use a standard audio cable to connect your video camera to the sync unit.
  4. Record your videos as you normally do. Take as many videos as you want.
  5. After the training, upload the sensor data from the athlete's to your cloud.
  6. Upload the videos and assign which video belongs to which athlete.
  7. Analyze your videos, the data is automatically overlaid.
Collage of the video synchronization. Left the webapp for uploading the video and right the video player with integrated data overlay.
Left: the webapp interface for adding a single video to a measurement. Only a title and the video-file need to be specified. Click on "Add Segment" and the video is uploaded and automatically synchronized with the data.
Right: the video player with the center of mass speed overlay. The graph is synchronized and plays with the video. Clicking anywhere on the curve moves the video to the same time. Videos can be played in slow motion and frame-by-frame.

When you take your videos you can put the sync unit into a pocket of your jacket. You can use multiple video cameras, all you need is one sync unit per camera. Each camera is completely independent and free to move around. There is no contact to the athlete sensors needed, the synchronization happens via the GPS-time. The videos can be of any length but should be at least 8 seconds long.

How are our customers using this tool?

Our interactive video analysis is mostly used for providing technical feedback to the athlete. The combination of objective data with visual images allows athletes to understand how their motion is affecting their performance. This raises their motion awareness. Athletes are able to faster and better process and anderstand coaching feedback and can therefore improve their performance much faster compared to regular video feedback and analysis.

Some teams go even one step further and have developed a dedicated coaching language based on our video analysis tools and color codes. They have now an incredibly efficient "coded" verbal feedback they are using during competitions where in a single word coaches can convey very complex concepts to athletes and athletes immediately understand what they should do.