Professional Video Analysis Tips
|Back to the main Video Analysis Page||The Rusty used to charge a whopping $20 to his friends on staff for unlimited computerized video movement analysis. This year he's doing it for free. Here's a description of the service he provides and how he does it. Hopefully it will give you an idea of what you can at your mountain.|
Rusty will tape the skier or rider on the slopes, digitize the clips and analyze the clips on his PC with the person being coached. Before the coaching session starts, Rusty will dub a high quality copy of the clips onto a video tape. When the analysis session is being conducted, the images on the PC monitor and the discussion between Rusty and the coachee are added on the video tape.
Here's how it works
In between classes and clinics, Rusty will go out on the slopes with his beat up old analog camera. For a typical person who is preparing for PSIA level 2 certification, Rusty will choose Whitetail's advanced beginner trail Snow Park. There are some man made snow "rollers" on skiers right that provide enough extra pitch to keep traffic light and allow for decent carved turns, plus a flat spot at the bottom of the run for beginner demos. The goal is to get 4-5 clips. After the run is complete, Rusty will send the skier or rider for a free run while he returns to the locker room to prepare for the analysis session.
The first thing Rusty does is pop the battery off the camcorder and put in a recharger. Then he hooks the camera up to AC power and connects the VCR video in cable to the camcorder video out connection. With the VCR set to video in feed, the TV monitor should show the runs taped on the hill. With the camcorder tape rewound to the beginning, Rusty will dub the clips onto a fresh video tape. This can get a little tricky if multiple people were taped in one session. When Rusty gets some more free time, he might get some loop music and mix in whatever ski or board sounds from the hill are available to add to the plain clips, but for now he just records the clips without sound.
Next Rusty rewinds the camcorder again and then hooks up to his computer. Rusty starts up the "record" piece of his analysis software and records each piece of the run on the hill into a separate video clip. Once all the clips are digitized, Rusty will review the clips to prepare notes for the analysis session. The analysis software that Rusty uses shows a frame number for each still frame within a clip. Rusty uses this frame number as a reference point within the clip. In addition to exactly marking specific frames and ranges of frames for analysis, Rusty will count the number of frames in between turns (for skiers this is from the point where the ski pole is vertical during the pole plant until the same point in the next turn in the same direction, for snowboarders things work a little different). Rusty then searches through his reference database for skier who has the same size turns as measured by the frame count (which is part of the filename).
As Rusty is examining the clips, he is searching for four things. First, everybody has something good going on in their skiing. Since most people immediately latch on to the bad things they can see, Rusty takes special care to have an equally long list of good things to point out. Next Rusty will look for symptoms of problems. Then Rusty will identify the root causes of symptoms. Finally, Rusty searches for specific segments of the clips that are particularly helpful for learning movement analysis. In these segments, something interesting must be happening. At the same time, the scene should clearly snow coming off the ski (when it does), the edge angle of the skis in the snow and a good view of all the body parts through the whole turn.
During the introduction to the session, Rusty will set the first clip to play in a loop and "speak the pitch" so some audio explanation of what the tape is about gets recorded. Next Rusty what the goals of the session are and will explain an overview of the good things and opportunities to be reviewed in the session. During the session, both Rusty's and the coachees comments are recorded on tape. Rusty will make extensive use of freeze frame and extreme slow motion to help illustrate the points being covered. For teaching the coachee how to do movement analysis, Rusty will use the scroll bar on the clip to replay a specific section at increasing speeds to help the coachee train their eyes to see things at full speed. During a session, there's a lot of hitting a spot, backing up a few frames, slowing moving forward, then backing up and replaying again and again so that the coachee can see what is going on and why things are happening. Whenever Rusty needs to point out specific things on the screen, he will use the mouse pointer so the area being pointed to is identified on the tape (it takes a bit of practice to not use your finger on the PC monitor). Rusty uses the straight line drawing tool to check shoulder and hand alignment. Rusty will use the angle measuring tool to measure the angle between the feet, hips and chin to quantify good angulation or banking. If turns to one side are better than the other, Rusty will use the split screen feature to compare left turns versus right turns. This is done by displaying the same clip in each of the split windows and using the digital flip capability to make a left turn in one window look like a right turn in the other. Since most skiers make rythmic turns, it's easy to synch up the clips. This makes it very easy to see what's happening in the good turn that needs to happen in the "bad" turn. Finally Rusty will pull up the reference clip to show the coachee how and when to make the different movements that are needed to improve their skiing. 20-30 minutes later
The Rusty has a four foot wide space along a locker room wall, plus the top of a refrigerator to work with. His equipment consists of:
Pentium 2 PC (!) (200MHZ, 4GB of disk space), monitor, and an analog digitizing card
Analog video camera with telephoto lens
(testing a wireless mic)
video mixer box
2 battery chargers
3 power strips
A boatload of audio and video cables
A spare box of video tapes and labels
A computer cable lock that can lock the PC, monitor, VCR and camcorder all into a single piece that is virtually impossible for a single person to just walk away with. However, this stuff is so old nobody would bother to steal it now.
Rusty is experimenting with the V1 Pro software. This software allows him to deliver a 10 minute coaching session over the Internet.
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