import os
for d, subd, files in os.walk(os.getcwd()):
    for fil in files:
        print(fil.__str__())
        print("")
        fil.__str__().find("mp4")
        if fil.__str__().find("mp4") == 5:
            print("Пошла жара")
            with open("out.mp4", "ab") as out_file, open(fil.__str__(), "rb") as in_file:
                out_file.write(in_file.read())