I don't know what a "synathesia video" is, but I increasingly think instruction videos are *potentially* helpful, both to learners and teachers alike. In fact, I have a goal to make some myself, starting over this year ... but, I have a lot of goals for over the year (read: more goals than I immediately know what to do with)
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I have not been an instruction video fiend over the years, but I have watched several performance videos of other people, and several instruction videos out of curiosity. I have learned something from some angle, or several things, from every one of them - even the ones where I completely do not find myself feeling in-line with the bottom line of the teaching.
It is not beyond my imagination to potentially find a teacher by way of stumbling across an instruction video that I could not ignore. Though it was not through instruction videos precisely, in some ways that is very similar to how I found two individuals who I ended up working with, one of whom I ended up studying with in person. In that respect, from a teacher's point of view, instruction videos can serve as advertisement at the cost of sharing useful information. Along those lines, I have a therapist friend who told me that some therapists are starting to post treatments (for free) online, for similar reasons.
Topic: Piano teaching site - Teaching opportunity