is your solution but interfaced (chained) with live MIDI stream input
via virtual keyboard taps (I am just working on)
Synthesia supports virtual keyboard taps while MIDI is played back
but generally fails to process polyphony multitaps correctly (have a try yourself)
If bugs with synthesia are solved correctly I go to Piano2MIDI or Sound2MIDI ...
I have been using this extension called "Youtube Playback Speed Control" for a long time to speed up YouTube videos, but it can be used to slow them down too.
From the description:
Youtube playback speed increase or decrease is just a mouse click ...
A small web-app that may be useful when analyzing or practicing with YouTube videos and offline media files (I am its author):
It has A-B repeat, fast/slow motion and loop bookmarking facilities.
Some more features:
The A-B loop window can be adjusted using a double-handled slider, ← & → on the keyboard, or, more ...
I'd probably recommend starting with the built-in YouTube controls. But for the sake of completeness here's another workflow that makes use of 3rd party software called a "phrase trainer" or "slow downer". Here's a list of them.
Typically, you'd download or otherwise record the audio from the video so that you have it locally. There are a ...
There are at least two options:
Option 1: You can slow down the video by changing the Playback Speed setting
Browser instructions (this link for further alternatives)
Click on the Settings menu icon.
Select Playback speed
Select the speed you want
Option 2: Go frame by frame
You can progress frame by frame using the ,
(backward) and . (forward) keys. (...