To improve videos for showing strokes -
1) Move the camera closer so that your feet and tip of your racket are always just within the frame (about 5% extra at top, bottom, sides).
Always include the ball impact.
2) Shoot your video in bright direct sunlight. Your smartphone camera has an AUTO exposure control and that probably will select a fast shutter speed in bright sunlight. The faster the shutter speed the less motion blur.
3) The motion of the serve is too fast to show at 30 fps or 60 fps. You need high speed video to see what is really happening. Search - Youtube + Sampras + serve + high speed video
There are lots of quality high speed videos of serves.
4) With high speed video you can see the fastest parts of the service motion adequately.
This and other 240 fps videos of serves on my Vimeo.
Stop-action single-frame is not that good on Vimeo or Youtube. The best that can be done viewing on site is to click the play-pause button as fast as possible. (If anyone downloads and views with Quicktime please let us know how the video works for stop action using the Quicktime forward & backward arrows.)
Notice: the straight arm at impact, the angle between the straight arm and the racket, the near straight line between his two shoulders and arm. Most importantly, you can see the largest contributor to racket head speed at impact - internal shoulder rotation
(ISR) (misnamed in usage 'pronation'). ISR can be seen by the very rapid rotation of the elbow bones, the rotation lasts only about 0.03 seconds. There are many discussions on this forum on internal shoulder rotation. Search this forum - serve + internal shoulder rotation + Toly