Comparing videos to ATP serves is the best information. For most accurate comparisons, the camera angles should be as close as possible to your camera angles.
Very few Youtube videos that were recorded with the camera on the ground so you will waste a lot of time finding ATP serves to compare when using a towel as a tripod. One of my cheap tripods cost about $20. A tall tripod was about $40. (Polaroid)
It is easier to first find an ATP Youtube taken with a ground level camera
mounted on a tripod - then duplicate the ATP serve video that you found.. Also, with camera looking along the ball's trajectory and showing the bounce. Then you can find very similar camera angles in ATP serves - because it is a very popular camera arrangement. This is particularly important to get the racket drop and show the orientation of the upper arm are out from the body to the side.
Videos from higher angles that show the ball bounce are my favorite for comparisons.
Best is an elevated camera from behind - camera looks right along the ball's trajectory and sees the bounce.
See ball spin and bounce.
But at the court you need a step ladder.
Hand held cameras work OK but you want to stay in one place and not be walking. A camera mounted on the fence does not work to cover the bounce as you need a steeper down angle to get the bounce with a close up as the ball flies away curving down.
Instead of camera looking along the ball's trajectory have it looking along the hand's path at the time of impact. That shows the hand path, and racket path with ISR at the time of impact and gives an indication of the angle of those paths to the ball's trajectory. Of course, the best camera for these paths is the camera overhead shot.
Only the high level serve technique with ISR will display this signature. See 1:05.
You need a recording frame rate of about 240 fps for tennis strokes and a very fast shutter speed to minimize motion blur. Most high speed cameras have automatic exposure control and it is difficult to know the shutter speed. Shutter speed is minimized in bright sunlight, so if you have too much motion blur video in bright sunlight. I still recommend the Casio cameras with high speed video modes. They are low resolution but have shutter speed down to 25 microseconds with full manual control. I bought a Casio Ex-FH100 used for $85.
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