Update cut_bs.py such that --frame and --length may be combined

    return fr_cnt

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

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

    # cut until start frame

    fr_cnt = 0

    cut_cnt = 0

    extracted_frames_cnt = 0

    for cur_frame in range(start_frame):

        sync_word = fp.read(2)

        if sync_word == b"":

            return (fr_cnt, cut_cnt)

            return (fr_cnt, extracted_frames_cnt)

        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)

        fr_cnt += 1

        cut_cnt += 1

    if start_with_sid:

        found = False

        while not found:

            sync_word = fp.read(2)

            if sync_word == b"":

                return (fr_cnt, cut_cnt)

                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]

            if n_bits in SID_BITS:

                found = True

                fp_out.write(sync_word)

                fp_out.write(n_bits_bs)

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

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

            else:

                fp.read(n_bits * 2)

                cut_cnt += 1

                fr_cnt += 1

    # transfer remaining frames

    while True:

    # 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!")

        fp_out.write(n_bits_bs)

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

        fr_cnt += 1

    return (fr_cnt, cut_cnt)

        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)

        fr_cnt += 1

    return (fr_cnt, extracted_frames_cnt)

if __name__ == "__main__":

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

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

            if my_args.sid or my_args.frame:

                fr_cnt, cut_cnt = cut_from_start(

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

            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

            )

                if my_args.sid and (fr_cnt == cut_cnt):

                    print("Warning! No SID frame found in bitstream!")

                print(f"Cut {cut_cnt} of {fr_cnt} frames from {my_args.bs_in}")

            elif my_args.length:

                fr_cnt = cut_to_length(fp_in, fp_out, my_args.length)

                if fr_cnt != my_args.length:

                    print(

                        f"Warning! Could not cut to length {my_args.length} as bitstream only contained {fr_cnt} frames!"

                    )

                print(f"Cut {my_args.bs_in} to {fr_cnt} frames")

            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}")