I use is CMV+ app. Cost $3.99.
Make sure to use app to record video at 240fps or better. Video from the side. Has very accurate stop watch in app.
Start at release. End at plate.
Take mound distance minus stride length. That is close to release to plate distance. Adjust back as needed.
Formula I use:
DistanceTime then ️ .682 = Avg velocity over the distance.
Then to get release velocity:
Distance2 then 5.5 (the factor for drag on a baseball) and add to avg speed and you will have speed at release.
So last pitch my 12 year old threw sat from 50 feet. Releases at 46 ft. His time from release to plate was .480 sec.
46.480=95.833 then 95.833 ️ .682= 65.35 avg mph for the distance.
462=23 feet. 235.5=4.18 mph add to avg.
4.18 + 65.35= 69.53 mph at release. Do the same but subtract 4.18 from avg to get speed at the plate.
I'll clean up an example if people want it.