check_playing_file.py

import os
import psutil

class CheckingVOD:
    def __init__(self):
        self.process = self.locate()
        self.refresh()

    def locate(self, name='potplayer'):
        pid = None

        for proc in psutil.process_iter():
            if name in proc.name().lower():
                pid = proc.pid

        if pid is None:
            raise OSError('Process not found')

        return psutil.Process(pid)

    def refresh(self):
        self.file_list = set()
        for item in self.process.open_files():
            self.file_list.add(os.path.basename(item.path))

    def check(self, fpath):
        if fpath in self.file_list:
            return True
        return False

    def check_dir(self, dir_path):
        for _, _, file_list in os.walk(dir_path):
            for file_name in file_list:
                if self.check(file_name):
                    return file_name
        return None

if __name__ == '__main__':
    print(CheckingVOD().check_dir(r'F:/Videos/Drill Team/'))