gistfile1.py

    found = -2
    if args.inposition < 0:
        args.inposition %= len([s for s in video.streams if s.fftype == "a"])
        args.inposition += 1
    i = 0
    left = args.inposition
    for stream in video.streams:
        if stream.fftype != "v" and found < -1:
            found = -1
        if left == 0 and found == -1:
            params += ["-map", "1:a:{}".format(args.outposition)]
            found = i
        if stream.fftype == "a":
            left -= 1
        params += ["-map", "0:{}".format(i)]
        i += 1
    if found < 0:
        params += ["-map", "1:a:{}".format(args.outposition)]
        found = i