Tennis video analysis – a Primer

I received a special gift from my lovely wife during last year’s Christmas.

It is an add-on lens to put on my iPhone to capture more area. It is particularly useful when recording the tennis match from the baseline, because my iPhone doesn’t have a wide angle lens built-in so it doesn’t capture enough area.

To be honest, originally I was just planning to try out the new AI feature offered by SwingVision app. After using it for over 6 weeks and multiple rounds of trial and errors, post game video has become an essential piece of my tennis life. The app itself is still in its infancy stage with all kinds of limitations, however I can see a lot of potential in this area.

Why (analyze your tennis video)

Reviewing and analyzing post game video is a proven method for athlete to improve the game. The famous Tom vs Time video has showed us that, even for legendary football player like Tom Brady, he still need to watch post game video on a daily basis to improve and prepare for his games.

For tennis enthusiasts,we are not professional athletes. We don’t have a team travelling around the world with us. That means very few of us have the resources to record and analyze our game.

Now with the development of the technology, specifically the improvement of cellphone camera, the newly improved SwingVision app, and roughly $60 add-ons (tripod and wide angle lens), we are (starting) to be able to enjoy the privilege of analyzing our own post-game video.

Here are what you can do with the video footage:

  • Objective view of what actually happened, instead of how you felt.
  • Revealing details that usually you are not aware of. For example, footwork and racket contact points.
  • Generate your own highlight reel and show it off in your social media feed

If you are parents or coaches of tennis players/athlete, it will offer additional benefits like providing precious material for off the court coaching.

What it is?

What is the big deal? You might ask this question. Isn’t it just record the game using your iPhone and then watch it later?

Recording the game isn’t hard. It is the post-processing part that turns people away.

For example if you play 90 minutes for a single match, the full video length is 90 minute. It has to be processed because

  • It takes up lots of space in your phone (at least 2gb even if you choose the lowest resolution 720p)
  • Roughly 60-70% of the video content is of no use. This include the warm up, between points time, resting between games etc.

Based on my experience, you can use two methods to process the video captured. Just to be clear, these two are not mutually exclusive so you can do it both.

Manual method

In the iOS environment, we can use the native iMovie app, exporting then trimming out all those non-value added content.

You can even add the score update as text, which will be very beneficial to other audience.

One additional benefit of editing the video manually by yourself is it is basically forcing yourself to do a post-morden analysis. The memory is still fresh. So when you are editing it, it is naturally intuitive to remind yourself on those critical, game changing points. Put them on slow mode, it will usually uncover insights. For example, you thought you lost the point by hitting too hard, but it is actually because the balls bounced a bit high due to the top-spin your opponents .

The only downside is – It is time consuming. For a game of 90 minutes, it will require at least 60min to edit it.

Automatic method

Using the SwingVision app to record the game. And it will be automatically trimmed by its A.I video processing technology.

It will also trim each shot by sho type and spin type, so it is quite effective if there is a skill (eg. backhand slice) you want to focus on improving. It is also providing interactive data point like the screenshots below.

The app actually provided a lot more data points. However these two charts are my favorite. They are intuitive to understand. Green dots are my forehands, and yellows are my backhands. By default it is giving you a snapshot of where are the place I hit the ball (racket contact) and where I dropped my balls (shot placement).

However, it doesn’t really mean anything beyond pretty graph. The analysis doesn’t kick in until we can segment the data out. With a few clicks, a much more insightful charts are showing below, segmenting my stats and my partners’ stats.

When comparing forehand stats, It is becoming apparent that my partner hit his forehand to my backhand(53%) significantly more than I did (20%). That wasn’t something I noticed during the game for sure.

For backhands, I noticed only 45% of my shots were falling behind the service line, while my partner has 64%. This definitely has sparked a recommendation for me, because I need to hit my backhand deeper. With this measurement tool in place, I now know this can be tracked and analyzed on a consistent basis.

How to use it

  1. Always ask permission from your opponent.
  2. Make sure the cellphone has at least 8GB of space.
  3. Install the wide angle lens into the cellphone camera, as well as attach the cellphone to the tripod.
  4. Place the tripod to the very back of the court. Making sure it is stable, as the balls can hit it
  5. Start the recording
  6. Play your normal tennis game, but do not switch sides
  7. Watch and analyze the post game video

What you should know

Following are the limitation of using the app right now for automated tracking. Hopefully it can be addressed in the future.

  • It takes up a lot of space in the phone. (seems to have a new feature in place in the beta version)
  • Can’s switch side when playing a match. This is quite annoying as I will expect the facial recognition technology is quite mature by now.
  • It can only track the game as a “practice” so there is no score tracking yet.
  • The data captured in apple watch doesn’t connect to the video yet if I choose the game type as a “match”. There it will show up as 2 games in my dataset(feed).

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