ff2mpv.py

#!/usr/bin/env python3
import sys, struct, json
from subprocess import Popen, DEVNULL

def main():
    message = get_message()
    url = message.get('url')
    args = ['mpv', '--no-terminal', '--', url]
    Popen(args, stdin=DEVNULL, stdout=DEVNULL, stderr=DEVNULL)
    # Need to respond something to avoid "Error: An unexpected error occurred"
    # in Browser Console.
    send_message('ok')


# https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Native_messaging#App_side
def get_message():
    raw_length = sys.stdin.buffer.read(4)
    if not raw_length:
        return {}
    length = struct.unpack('@I', raw_length)[0]
    message = sys.stdin.buffer.read(length).decode('utf-8')
    return json.loads(message)


def send_message(message):
    content = json.dumps(message).encode('utf-8')
    length = struct.pack('@I', len(content))
    sys.stdout.buffer.write(length)
    sys.stdout.buffer.write(content)
    sys.stdout.buffer.flush()


if __name__ == '__main__':
    main()