With this script you can generate a button on youtube/twitch player that sends the stream/video to streamlink
These instructions are for windows

---SETUP INFO---
First get a copy of streamlink

Create a file called parse.cmd in your streamlink folder and paste these contents in
Modify the video player variable to point to your player of choice

@echo off
set "player=C:\Program Files\MPC-HC\mpc-hc64.exe"
set "str=%~1"
set "str=%str:streamlink://=%"
start "" "%~dp0streamlink.exe" --player "%player%" "%str%" best
exit 0

After that open a command prompt as admin and run these two commands
The highlighted part is the path to your streamlink folder and parse.cmd, change this to yours
reg add "HKCR\streamlink" /v "URL protocol" /t REG_SZ /d "" /f
reg add "HKCR\streamlink\shell\open\command" /ve /t REG_SZ /d "\"C:\Program Files (x86)\Streamlink\bin\parse.cmd\" \"%1\"" /f
After all this is done, you can install this script