Here's a marked up example of a dumbbell power snatch:
At different points in the lift the video is paused or put in slow motion to show good spinal alignment, good vertical lift and leaning the body backwards, but bad position of the dumbbell, not getting the body low enough to receive the weight, and not having the arm fully extended on the catch.
This split screen video shows good and poor form of a lunge for comparison:
In the left frame, note how the left knee collapses inward on landing. The torso rounds forward, and the medicine ball is never lifted fully overhead as on the right.
While these examples are finished edits, the video can be annotated and the playback speed manipulated on the spot. This gives immediate feedback for optimal learning and the opportunity to practice better technique.
The other app to help with your training is an interval timer, complete with bells and whistles:
No more will a forgetful trainer make you repeat an exercise! The interval name, time remaining in the interval, intervals left, etc. are shown, and there are audible tones to begin and end each interval. Remember, it's not the trainer making you work so hard, it's the app.
Besides these, normal communication and productively apps make it easy for me to base my training business outdoors. Here's my office at the Steven Rice Fitness International Headquarters in Mitchell Park Palo Alto: