check the html source code of the reviewer and what the media buttons do. They send some code to python with pycmd. on the python side in aqt/reviewer.py you have a a linkhandler command that catches those “signals” coming from js, see anki/qt/aqt/reviewer.py at fd013f68d2de8cfc58a6f4ecce4519e6c3acd260 · ankitects/anki · GitHub
To learn about the reviewer webview there’s:
You can now debug the webviews using an external Chrome instance, by setting the env var QTWEBENGINE_REMOTE_DEBUGGING to 8080 prior to starting Anki, then surfing to localhost:8080 in Chrome.
Porting 2.0 Add-ons - Writing Anki Add-ons. this is also in an add-on named AnkiWebView Inspector.
To send the pycmd play in the webview side I guess you have some sort of clickable hyperlink where the target is maybe a js function that emits play: … So when you right click the button you maybe have this link data and - similar to my hyperlink detection in my add hyperlink add-on - you can analyze each link clicked