Clean up cut_bs.py

SID_BITS = {35, 48, 104}

SYNC_WORDS = {b"!k", b" k"}

def cut_from_start(fp, fp_out, start_frame=0, length=-1, start_with_sid=False):

    # cut until start frame

    fr_cnt = 0

    extracted_frames_cnt = 0

    for cur_frame in range(start_frame):

def get_next_frame(fp):

    eof = False

    n_bits = 0

    data = None

    sync_word = fp.read(2)

    if sync_word == b"":

            return (fr_cnt, extracted_frames_cnt)

        eof = True

        return (sync_word, n_bits, data, eof)

    if sync_word not in SYNC_WORDS:

        raise ValueError("Bad Sync word!")

    n_bits = struct.unpack("h", fp.read(2))[0]

        fp.read(n_bits * 2)

    data = fp.read(n_bits * 2)

    return (sync_word, n_bits, data, eof)

def write_frame(fp_out, sync_word, n_bits, data):

    fp_out.write(sync_word)

    fp_out.write(struct.pack("h", n_bits))

    fp_out.write(data)

def cut_from_start(fp, fp_out, start_frame=0, length=-1, start_with_sid=False):

    fr_cnt = 0

    extracted_frames_cnt = 0

    eof = False

    # cut until start frame

    while fr_cnt < start_frame and not eof:

        (sync_word, n_bits, data, eof) = get_next_frame(fp)

        if not eof:

            fr_cnt += 1

    # cut until SID frame

    if start_with_sid:

        found = False

        while not found:

            sync_word = fp.read(2)

            if sync_word == b"":

                return (fr_cnt, extracted_frames_cnt)

            if sync_word not in SYNC_WORDS:

                raise ValueError("Bad Sync word!")

            n_bits_bs = fp.read(2)

            n_bits = struct.unpack("h", n_bits_bs)[0]

        while not found and not eof:

            (sync_word, n_bits, data, eof) = get_next_frame(fp)

            if not eof:

                fr_cnt += 1

                if n_bits in SID_BITS:

                    found = True

                fp.seek(-4,1) # Found SID frame, go back

            else:

                fp.read(n_bits * 2)

                fr_cnt += 1

                    fp.seek(-(4 + n_bits * 2), 1)  # Found SID, rewind

    # transfer frames

    eof = False

    while length != 0:

        sync_word = fp.read(2)

        if sync_word == b"":

            eof = True

            break

        if sync_word not in SYNC_WORDS:

            raise ValueError("Bad Sync word!")

        n_bits_bs = fp.read(2)

        n_bits = struct.unpack("h", n_bits_bs)[0]

        fp_out.write(sync_word)

        fp_out.write(n_bits_bs)

        fp_out.write(fp.read(n_bits * 2))

    while length != 0 and not eof:

        (sync_word, n_bits, data, eof) = get_next_frame(fp)

        if not eof:

            write_frame(fp_out, sync_word, n_bits, data)

            fr_cnt += 1

            extracted_frames_cnt += 1

            length -= 1

    # count remaining frames, if any

    while not eof:

        sync_word = fp.read(2)

        if sync_word == b"":

            eof = True

            break

        if sync_word not in SYNC_WORDS:

            raise ValueError("Bad Sync word!")

        n_bits_bs = fp.read(2)

        n_bits = struct.unpack("h", n_bits_bs)[0]

        fp.read(n_bits * 2)

        (sync_word, n_bits, data, eof) = get_next_frame(fp)

        if not eof:

            fr_cnt += 1

    return (fr_cnt, extracted_frames_cnt)

    if not os.path.exists(os.path.realpath(my_args.bs_in)):

        print(f"\nInput file {my_args.bs_in} does not exist!")

        sys.exit(-1)

    if not os.path.exists(os.path.realpath(my_args.bs_out)):

        print(f"\nOutput file {my_args.bs_out} does not exist, creating it!")

    else:

        print(f"\nOutput file {my_args.bs_out} does exist, overwriting it!")

    if os.path.exists(os.path.realpath(my_args.bs_out)):

        print(f"\nOutput file {my_args.bs_out} exists, overwriting it!")

    with open(my_args.bs_in, "rb") as fp_in:

        with open(my_args.bs_out, "wb") as fp_out:

            fr_cnt, extracted_frames_cnt = cut_from_start(

                fp_in, fp_out, start_frame=my_args.frame, length=my_args.length, start_with_sid=my_args.sid

                fp_in,

                fp_out,

                start_frame=my_args.frame,

                length=my_args.length,

                start_with_sid=my_args.sid,

            )

            if extracted_frames_cnt == 0:

                print(f"\nExtracted 0 frames!")

                sys.exit(-1)

            if (my_args.length != -1 and extracted_frames_cnt != my_args.length):

                print(f"Warning! Requested {my_args.length}, only {extracted_frames_cnt} obtained!")

            print(f"Extracted {extracted_frames_cnt} out of {fr_cnt} frames from {my_args.bs_in}")

            if my_args.length != -1 and extracted_frames_cnt != my_args.length:

                print(

                    f"Warning! Requested {my_args.length}, only {extracted_frames_cnt} obtained!"

                )

            print(

                f"Extracted {extracted_frames_cnt} out of {fr_cnt} frames from {my_args.bs_in}"

            )