I am very interested in what you find. I have looked for a way to use my smartphone at the courts, especially to view Youtubes with singe frame. Single frame works great on a laptop but nothing so far for a smartphone. I hope you find some applications that make a smartphone useful on court. Do you use the high speed video mode from the smartphone?
Kinovea does a wonderful job and has lots of capabilities. For stroke analysis my old version of Kinovea has a count down timer. You can set it to be 0 milliseconds at the frame closest to impact. Then all the frame times give the time before impact, as for example, -486 ms before impact. That's 486 milliseconds before impact. Once you learn that count down timer, all videos can easily have a time line.
Video with Kinovea time scale, pause frame to read text, text on pauses. Many other capabilities are available.
Kinovea works very well for videos that you take or videos on your computer. But Youtube is a streaming service and downloading their videos became problematic.
I found a technique where two Youtubes or Vimeos or one of each - total or 5, can be compared on the TT forum. Simply paste them one above the other and follow my directions. If you do not want to post your videos, it will also work on forum 'Conversation'. But you cannot have a Conversation with yourself. You need another forum member to cooperate with you.
For cameras, I still like the Casio Ex FH100 camera, because it has full manual exposure control and a shutter speed down to 40 microseconds. I found two FH100's used, one was $85. Both worked fine. These were designed for high speed video.
