mediaflow_proxy/drm/decrypter.py

import argparse
import struct
import sys

from Crypto.Cipher import AES
from collections import namedtuple
import array

CENCSampleAuxiliaryDataFormat = namedtuple("CENCSampleAuxiliaryDataFormat", ["is_encrypted", "iv", "sub_samples"])


class MP4Atom:
    """
    Represents an MP4 atom, which is a basic unit of data in an MP4 file.
    Each atom contains a header (size and type) and data.
    """

    __slots__ = ("atom_type", "size", "data")

    def __init__(self, atom_type: bytes, size: int, data: memoryview | bytearray):
        """
        Initializes an MP4Atom instance.

        Args:
            atom_type (bytes): The type of the atom.
            size (int): The size of the atom.
            data (memoryview | bytearray): The data contained in the atom.
        """
        self.atom_type = atom_type
        self.size = size
        self.data = data

    def __repr__(self):
        return f"<MP4Atom type={self.atom_type}, size={self.size}>"

    def pack(self):
        """
        Packs the atom into binary data.

        Returns:
            bytes: Packed binary data with size, type, and data.
        """
        return struct.pack(">I", self.size) + self.atom_type + self.data


class MP4Parser:
    """
    Parses MP4 data to extract atoms and their structure.
    """

    def __init__(self, data: memoryview):
        """
        Initializes an MP4Parser instance.

        Args:
            data (memoryview): The binary data of the MP4 file.
        """
        self.data = data
        self.position = 0

    def read_atom(self) -> MP4Atom | None:
        """
        Reads the next atom from the data.

        Returns:
            MP4Atom | None: MP4Atom object or None if no more atoms are available.
        """
        pos = self.position
        if pos + 8 > len(self.data):
            return None

        size, atom_type = struct.unpack_from(">I4s", self.data, pos)
        pos += 8

        if size == 1:
            if pos + 8 > len(self.data):
                return None
            size = struct.unpack_from(">Q", self.data, pos)[0]
            pos += 8

        if size < 8 or pos + size - 8 > len(self.data):
            return None

        atom_data = self.data[pos : pos + size - 8]
        self.position = pos + size - 8
        return MP4Atom(atom_type, size, atom_data)

    def list_atoms(self) -> list[MP4Atom]:
        """
        Lists all atoms in the data.

        Returns:
            list[MP4Atom]: List of MP4Atom objects.
        """
        atoms = []
        original_position = self.position
        self.position = 0
        while self.position + 8 <= len(self.data):
            atom = self.read_atom()
            if not atom:
                break
            atoms.append(atom)
        self.position = original_position
        return atoms

    def _read_atom_at(self, pos: int, end: int) -> MP4Atom | None:
        if pos + 8 > end:
            return None

        size, atom_type = struct.unpack_from(">I4s", self.data, pos)
        pos += 8

        if size == 1:
            if pos + 8 > end:
                return None
            size = struct.unpack_from(">Q", self.data, pos)[0]
            pos += 8

        if size < 8 or pos + size - 8 > end:
            return None

        atom_data = self.data[pos : pos + size - 8]
        return MP4Atom(atom_type, size, atom_data)

    def print_atoms_structure(self, indent: int = 0):
        """
        Prints the structure of all atoms in the data.

        Args:
            indent (int): The indentation level for printing.
        """
        pos = 0
        end = len(self.data)
        while pos + 8 <= end:
            atom = self._read_atom_at(pos, end)
            if not atom:
                break
            self.print_single_atom_structure(atom, pos, indent)
            pos += atom.size

    def print_single_atom_structure(self, atom: MP4Atom, parent_position: int, indent: int):
        """
        Prints the structure of a single atom.

        Args:
            atom (MP4Atom): The atom to print.
            parent_position (int): The position of the parent atom.
            indent (int): The indentation level for printing.
        """
        try:
            atom_type = atom.atom_type.decode("utf-8")
        except UnicodeDecodeError:
            atom_type = repr(atom.atom_type)
        print(" " * indent + f"Type: {atom_type}, Size: {atom.size}")

        child_pos = 0
        child_end = len(atom.data)
        while child_pos + 8 <= child_end:
            child_atom = self._read_atom_at(parent_position + 8 + child_pos, parent_position + 8 + child_end)
            if not child_atom:
                break
            self.print_single_atom_structure(child_atom, parent_position, indent + 2)
            child_pos += child_atom.size


class MP4Decrypter:
    """
    Class to handle the decryption of CENC encrypted MP4 segments.

    Attributes:
        key_map (dict[bytes, bytes]): Mapping of track IDs to decryption keys.
        current_key (bytes | None): Current decryption key.
        trun_sample_sizes (array.array): Array of sample sizes from the 'trun' box.
        current_sample_info (list): List of sample information from the 'senc' box.
        encryption_overhead (int): Total size of encryption-related boxes.
    """

    def __init__(self, key_map: dict[bytes, bytes]):
        """
        Initializes the MP4Decrypter with a key map.

        Args:
            key_map (dict[bytes, bytes]): Mapping of track IDs to decryption keys.
        """
        self.key_map = key_map
        self.current_key = None
        self.trun_sample_sizes = array.array("I")
        self.current_sample_info = []
        self.encryption_overhead = 0

    def decrypt_segment(self, combined_segment: bytes) -> bytes:
        """
        Decrypts a combined MP4 segment.

        Args:
            combined_segment (bytes): Combined initialization and media segment.

        Returns:
            bytes: Decrypted segment content.
        """
        data = memoryview(combined_segment)
        parser = MP4Parser(data)
        atoms = parser.list_atoms()

        atom_process_order = [b"moov", b"moof", b"sidx", b"mdat"]

        processed_atoms = {}
        for atom_type in atom_process_order:
            if atom := next((a for a in atoms if a.atom_type == atom_type), None):
                processed_atoms[atom_type] = self._process_atom(atom_type, atom)

        result = bytearray()
        for atom in atoms:
            if atom.atom_type in processed_atoms:
                processed_atom = processed_atoms[atom.atom_type]
                result.extend(processed_atom.pack())
            else:
                result.extend(atom.pack())

        return bytes(result)

    def _process_atom(self, atom_type: bytes, atom: MP4Atom) -> MP4Atom:
        """
        Processes an MP4 atom based on its type.

        Args:
            atom_type (bytes): Type of the atom.
            atom (MP4Atom): The atom to process.

        Returns:
            MP4Atom: Processed atom.
        """
        match atom_type:
            case b"moov":
                return self._process_moov(atom)
            case b"moof":
                return self._process_moof(atom)
            case b"sidx":
                return self._process_sidx(atom)
            case b"mdat":
                return self._decrypt_mdat(atom)
            case _:
                return atom

    def _process_moov(self, moov: MP4Atom) -> MP4Atom:
        """
        Processes the 'moov' (Movie) atom, which contains metadata about the entire presentation.
        This includes information about tracks, media data, and other movie-level metadata.

        Args:
            moov (MP4Atom): The 'moov' atom to process.

        Returns:
            MP4Atom: Processed 'moov' atom with updated track information.
        """
        parser = MP4Parser(moov.data)
        new_moov_data = bytearray()

        for atom in iter(parser.read_atom, None):
            if atom.atom_type == b"trak":
                new_trak = self._process_trak(atom)
                new_moov_data.extend(new_trak.pack())
            elif atom.atom_type != b"pssh":
                # Skip PSSH boxes as they are not needed in the decrypted output
                new_moov_data.extend(atom.pack())

        return MP4Atom(b"moov", len(new_moov_data) + 8, new_moov_data)

    def _process_moof(self, moof: MP4Atom) -> MP4Atom:
        """
        Processes the 'moov' (Movie) atom, which contains metadata about the entire presentation.
        This includes information about tracks, media data, and other movie-level metadata.

        Args:
            moov (MP4Atom): The 'moov' atom to process.

        Returns:
            MP4Atom: Processed 'moov' atom with updated track information.
        """
        parser = MP4Parser(moof.data)
        new_moof_data = bytearray()

        for atom in iter(parser.read_atom, None):
            if atom.atom_type == b"traf":
                new_traf = self._process_traf(atom)
                new_moof_data.extend(new_traf.pack())
            else:
                new_moof_data.extend(atom.pack())

        return MP4Atom(b"moof", len(new_moof_data) + 8, new_moof_data)

    def _process_traf(self, traf: MP4Atom) -> MP4Atom:
        """
        Processes the 'traf' (Track Fragment) atom, which contains information about a track fragment.
        This includes sample information, sample encryption data, and other track-level metadata.

        Args:
            traf (MP4Atom): The 'traf' atom to process.

        Returns:
            MP4Atom: Processed 'traf' atom with updated sample information.
        """
        parser = MP4Parser(traf.data)
        new_traf_data = bytearray()
        tfhd = None
        sample_count = 0
        sample_info = []

        atoms = parser.list_atoms()

        # calculate encryption_overhead earlier to avoid dependency on trun
        self.encryption_overhead = sum(a.size for a in atoms if a.atom_type in {b"senc", b"saiz", b"saio"})

        for atom in atoms:
            if atom.atom_type == b"tfhd":
                tfhd = atom
                new_traf_data.extend(atom.pack())
            elif atom.atom_type == b"trun":
                sample_count = self._process_trun(atom)
                new_trun = self._modify_trun(atom)
                new_traf_data.extend(new_trun.pack())
            elif atom.atom_type == b"senc":
                # Parse senc but don't include it in the new decrypted traf data and similarly don't include saiz and saio
                sample_info = self._parse_senc(atom, sample_count)
            elif atom.atom_type not in {b"saiz", b"saio"}:
                new_traf_data.extend(atom.pack())

        if tfhd:
            tfhd_track_id = struct.unpack_from(">I", tfhd.data, 4)[0]
            self.current_key = self._get_key_for_track(tfhd_track_id)
            self.current_sample_info = sample_info

        return MP4Atom(b"traf", len(new_traf_data) + 8, new_traf_data)

    def _decrypt_mdat(self, mdat: MP4Atom) -> MP4Atom:
        """
        Decrypts the 'mdat' (Media Data) atom, which contains the actual media data (audio, video, etc.).
        The decryption is performed using the current decryption key and sample information.

        Args:
            mdat (MP4Atom): The 'mdat' atom to decrypt.

        Returns:
            MP4Atom: Decrypted 'mdat' atom with decrypted media data.
        """
        if not self.current_key or not self.current_sample_info:
            return mdat  # Return original mdat if we don't have decryption info

        decrypted_samples = bytearray()
        mdat_data = mdat.data
        position = 0

        for i, info in enumerate(self.current_sample_info):
            if position >= len(mdat_data):
                break  # No more data to process

            sample_size = self.trun_sample_sizes[i] if i < len(self.trun_sample_sizes) else len(mdat_data) - position
            sample = mdat_data[position : position + sample_size]
            position += sample_size
            decrypted_sample = self._process_sample(sample, info, self.current_key)
            decrypted_samples.extend(decrypted_sample)

        return MP4Atom(b"mdat", len(decrypted_samples) + 8, decrypted_samples)

    def _parse_senc(self, senc: MP4Atom, sample_count: int) -> list[CENCSampleAuxiliaryDataFormat]:
        """
        Parses the 'senc' (Sample Encryption) atom, which contains encryption information for samples.
        This includes initialization vectors (IVs) and sub-sample encryption data.

        Args:
            senc (MP4Atom): The 'senc' atom to parse.
            sample_count (int): The number of samples.

        Returns:
            list[CENCSampleAuxiliaryDataFormat]: List of sample auxiliary data formats with encryption information.
        """
        data = memoryview(senc.data)
        version_flags = struct.unpack_from(">I", data, 0)[0]
        version, flags = version_flags >> 24, version_flags & 0xFFFFFF
        position = 4

        if version == 0:
            sample_count = struct.unpack_from(">I", data, position)[0]
            position += 4

        sample_info = []
        for _ in range(sample_count):
            if position + 8 > len(data):
                break

            iv = data[position : position + 8].tobytes()
            position += 8

            sub_samples = []
            if flags & 0x000002 and position + 2 <= len(data):  # Check if subsample information is present
                subsample_count = struct.unpack_from(">H", data, position)[0]
                position += 2

                for _ in range(subsample_count):
                    if position + 6 <= len(data):
                        clear_bytes, encrypted_bytes = struct.unpack_from(">HI", data, position)
                        position += 6
                        sub_samples.append((clear_bytes, encrypted_bytes))
                    else:
                        break

            sample_info.append(CENCSampleAuxiliaryDataFormat(True, iv, sub_samples))

        return sample_info

    def _get_key_for_track(self, track_id: int) -> bytes:
        """
        Retrieves the decryption key for a given track ID from the key map.

        Args:
            track_id (int): The track ID.

        Returns:
            bytes: The decryption key for the specified track ID.
        """
        if len(self.key_map) == 1:
            return next(iter(self.key_map.values()))
        key = self.key_map.get(track_id.pack(4, "big"))
        if not key:
            raise ValueError(f"No key found for track ID {track_id}")
        return key

    @staticmethod
    def _process_sample(
        sample: memoryview, sample_info: CENCSampleAuxiliaryDataFormat, key: bytes
    ) -> memoryview | bytearray | bytes:
        """
        Processes and decrypts a sample using the provided sample information and decryption key.
        This includes handling sub-sample encryption if present.

        Args:
            sample (memoryview): The sample data.
            sample_info (CENCSampleAuxiliaryDataFormat): The sample auxiliary data format with encryption information.
            key (bytes): The decryption key.

        Returns:
            memoryview | bytearray | bytes: The decrypted sample.
        """
        if not sample_info.is_encrypted:
            return sample

        # pad IV to 16 bytes
        iv = sample_info.iv + b"\x00" * (16 - len(sample_info.iv))
        cipher = AES.new(key, AES.MODE_CTR, initial_value=iv, nonce=b"")

        if not sample_info.sub_samples:
            # If there are no sub_samples, decrypt the entire sample
            return cipher.decrypt(sample)

        result = bytearray()
        offset = 0
        for clear_bytes, encrypted_bytes in sample_info.sub_samples:
            result.extend(sample[offset : offset + clear_bytes])
            offset += clear_bytes
            result.extend(cipher.decrypt(sample[offset : offset + encrypted_bytes]))
            offset += encrypted_bytes

        # If there's any remaining data, treat it as encrypted
        if offset < len(sample):
            result.extend(cipher.decrypt(sample[offset:]))

        return result

    def _process_trun(self, trun: MP4Atom) -> int:
        """
        Processes the 'trun' (Track Fragment Run) atom, which contains information about the samples in a track fragment.
        This includes sample sizes, durations, flags, and composition time offsets.

        Args:
            trun (MP4Atom): The 'trun' atom to process.

        Returns:
            int: The number of samples in the 'trun' atom.
        """
        trun_flags, sample_count = struct.unpack_from(">II", trun.data, 0)
        data_offset = 8

        if trun_flags & 0x000001:
            data_offset += 4
        if trun_flags & 0x000004:
            data_offset += 4

        self.trun_sample_sizes = array.array("I")

        for _ in range(sample_count):
            if trun_flags & 0x000100:  # sample-duration-present flag
                data_offset += 4
            if trun_flags & 0x000200:  # sample-size-present flag
                sample_size = struct.unpack_from(">I", trun.data, data_offset)[0]
                self.trun_sample_sizes.append(sample_size)
                data_offset += 4
            else:
                self.trun_sample_sizes.append(0)  # Using 0 instead of None for uniformity in the array
            if trun_flags & 0x000400:  # sample-flags-present flag
                data_offset += 4
            if trun_flags & 0x000800:  # sample-composition-time-offsets-present flag
                data_offset += 4

        return sample_count

    def _modify_trun(self, trun: MP4Atom) -> MP4Atom:
        """
        Modifies the 'trun' (Track Fragment Run) atom to update the data offset.
        This is necessary to account for the encryption overhead.

        Args:
            trun (MP4Atom): The 'trun' atom to modify.

        Returns:
            MP4Atom: Modified 'trun' atom with updated data offset.
        """
        trun_data = bytearray(trun.data)
        current_flags = struct.unpack_from(">I", trun_data, 0)[0] & 0xFFFFFF

        # If the data-offset-present flag is set, update the data offset to account for encryption overhead
        if current_flags & 0x000001:
            current_data_offset = struct.unpack_from(">i", trun_data, 8)[0]
            struct.pack_into(">i", trun_data, 8, current_data_offset - self.encryption_overhead)

        return MP4Atom(b"trun", len(trun_data) + 8, trun_data)

    def _process_sidx(self, sidx: MP4Atom) -> MP4Atom:
        """
        Processes the 'sidx' (Segment Index) atom, which contains indexing information for media segments.
        This includes references to media segments and their durations.

        Args:
            sidx (MP4Atom): The 'sidx' atom to process.

        Returns:
            MP4Atom: Processed 'sidx' atom with updated segment references.
        """
        sidx_data = bytearray(sidx.data)

        current_size = struct.unpack_from(">I", sidx_data, 32)[0]
        reference_type = current_size >> 31
        current_referenced_size = current_size & 0x7FFFFFFF

        # Remove encryption overhead from referenced size
        new_referenced_size = current_referenced_size - self.encryption_overhead
        new_size = (reference_type << 31) | new_referenced_size
        struct.pack_into(">I", sidx_data, 32, new_size)

        return MP4Atom(b"sidx", len(sidx_data) + 8, sidx_data)

    def _process_trak(self, trak: MP4Atom) -> MP4Atom:
        """
        Processes the 'trak' (Track) atom, which contains information about a single track in the movie.
        This includes track header, media information, and other track-level metadata.

        Args:
            trak (MP4Atom): The 'trak' atom to process.

        Returns:
            MP4Atom: Processed 'trak' atom with updated track information.
        """
        parser = MP4Parser(trak.data)
        new_trak_data = bytearray()

        for atom in iter(parser.read_atom, None):
            if atom.atom_type == b"mdia":
                new_mdia = self._process_mdia(atom)
                new_trak_data.extend(new_mdia.pack())
            else:
                new_trak_data.extend(atom.pack())

        return MP4Atom(b"trak", len(new_trak_data) + 8, new_trak_data)

    def _process_mdia(self, mdia: MP4Atom) -> MP4Atom:
        """
        Processes the 'mdia' (Media) atom, which contains media information for a track.
        This includes media header, handler reference, and media information container.

        Args:
            mdia (MP4Atom): The 'mdia' atom to process.

        Returns:
            MP4Atom: Processed 'mdia' atom with updated media information.
        """
        parser = MP4Parser(mdia.data)
        new_mdia_data = bytearray()

        for atom in iter(parser.read_atom, None):
            if atom.atom_type == b"minf":
                new_minf = self._process_minf(atom)
                new_mdia_data.extend(new_minf.pack())
            else:
                new_mdia_data.extend(atom.pack())

        return MP4Atom(b"mdia", len(new_mdia_data) + 8, new_mdia_data)

    def _process_minf(self, minf: MP4Atom) -> MP4Atom:
        """
        Processes the 'minf' (Media Information) atom, which contains information about the media data in a track.
        This includes data information, sample table, and other media-level metadata.

        Args:
            minf (MP4Atom): The 'minf' atom to process.

        Returns:
            MP4Atom: Processed 'minf' atom with updated media information.
        """
        parser = MP4Parser(minf.data)
        new_minf_data = bytearray()

        for atom in iter(parser.read_atom, None):
            if atom.atom_type == b"stbl":
                new_stbl = self._process_stbl(atom)
                new_minf_data.extend(new_stbl.pack())
            else:
                new_minf_data.extend(atom.pack())

        return MP4Atom(b"minf", len(new_minf_data) + 8, new_minf_data)

    def _process_stbl(self, stbl: MP4Atom) -> MP4Atom:
        """
        Processes the 'stbl' (Sample Table) atom, which contains information about the samples in a track.
        This includes sample descriptions, sample sizes, sample times, and other sample-level metadata.

        Args:
            stbl (MP4Atom): The 'stbl' atom to process.

        Returns:
            MP4Atom: Processed 'stbl' atom with updated sample information.
        """
        parser = MP4Parser(stbl.data)
        new_stbl_data = bytearray()

        for atom in iter(parser.read_atom, None):
            if atom.atom_type == b"stsd":
                new_stsd = self._process_stsd(atom)
                new_stbl_data.extend(new_stsd.pack())
            else:
                new_stbl_data.extend(atom.pack())

        return MP4Atom(b"stbl", len(new_stbl_data) + 8, new_stbl_data)

    def _process_stsd(self, stsd: MP4Atom) -> MP4Atom:
        """
        Processes the 'stsd' (Sample Description) atom, which contains descriptions of the sample entries in a track.
        This includes codec information, sample entry details, and other sample description metadata.

        Args:
            stsd (MP4Atom): The 'stsd' atom to process.

        Returns:
            MP4Atom: Processed 'stsd' atom with updated sample descriptions.
        """
        parser = MP4Parser(stsd.data)
        entry_count = struct.unpack_from(">I", parser.data, 4)[0]
        new_stsd_data = bytearray(stsd.data[:8])

        parser.position = 8  # Move past version_flags and entry_count

        for _ in range(entry_count):
            sample_entry = parser.read_atom()
            if not sample_entry:
                break

            processed_entry = self._process_sample_entry(sample_entry)
            new_stsd_data.extend(processed_entry.pack())

        return MP4Atom(b"stsd", len(new_stsd_data) + 8, new_stsd_data)

    def _process_sample_entry(self, entry: MP4Atom) -> MP4Atom:
        """
        Processes a sample entry atom, which contains information about a specific type of sample.
        This includes codec-specific information and other sample entry details.

        Args:
            entry (MP4Atom): The sample entry atom to process.

        Returns:
            MP4Atom: Processed sample entry atom with updated information.
        """
        # Determine the size of fixed fields based on sample entry type
        if entry.atom_type in {b"mp4a", b"enca"}:
            fixed_size = 28  # 8 bytes for size, type and reserved, 20 bytes for fixed fields in Audio Sample Entry.
        elif entry.atom_type in {b"mp4v", b"encv", b"avc1", b"hev1", b"hvc1"}:
            fixed_size = 78  # 8 bytes for size, type and reserved, 70 bytes for fixed fields in Video Sample Entry.
        else:
            fixed_size = 16  # 8 bytes for size, type and reserved, 8 bytes for fixed fields in other Sample Entries.

        new_entry_data = bytearray(entry.data[:fixed_size])
        parser = MP4Parser(entry.data[fixed_size:])
        codec_format = None

        for atom in iter(parser.read_atom, None):
            if atom.atom_type in {b"sinf", b"schi", b"tenc", b"schm"}:
                if atom.atom_type == b"sinf":
                    codec_format = self._extract_codec_format(atom)
                continue  # Skip encryption-related atoms
            new_entry_data.extend(atom.pack())

        # Replace the atom type with the extracted codec format
        new_type = codec_format if codec_format else entry.atom_type
        return MP4Atom(new_type, len(new_entry_data) + 8, new_entry_data)

    def _extract_codec_format(self, sinf: MP4Atom) -> bytes | None:
        """
        Extracts the codec format from the 'sinf' (Protection Scheme Information) atom.
        This includes information about the original format of the protected content.

        Args:
            sinf (MP4Atom): The 'sinf' atom to extract from.

        Returns:
            bytes | None: The codec format or None if not found.
        """
        parser = MP4Parser(sinf.data)
        for atom in iter(parser.read_atom, None):
            if atom.atom_type == b"frma":
                return atom.data
        return None


def decrypt_segment(init_segment: bytes, segment_content: bytes, key_id: str, key: str) -> bytes:
    """
    Decrypts a CENC encrypted MP4 segment.

    Args:
        init_segment (bytes): Initialization segment data.
        segment_content (bytes): Encrypted segment content.
        key_id (str): Key ID in hexadecimal format.
        key (str): Key in hexadecimal format.
    """
    key_map = {bytes.fromhex(key_id): bytes.fromhex(key)}
    decrypter = MP4Decrypter(key_map)
    decrypted_content = decrypter.decrypt_segment(init_segment + segment_content)
    return decrypted_content


def cli():
    """
    Command line interface for decrypting a CENC encrypted MP4 segment.
    """
    init_segment = b""

    if args.init and args.segment:
        with open(args.init, "rb") as f:
            init_segment = f.read()
        with open(args.segment, "rb") as f:
            segment_content = f.read()
    elif args.combined_segment:
        with open(args.combined_segment, "rb") as f:
            segment_content = f.read()
    else:
        print("Usage: python mp4decrypt.py --help")
        sys.exit(1)

    try:
        decrypted_segment = decrypt_segment(init_segment, segment_content, args.key_id, args.key)
        print(f"Decrypted content size is {len(decrypted_segment)} bytes")
        with open(args.output, "wb") as f:
            f.write(decrypted_segment)
        print(f"Decrypted segment written to {args.output}")
    except Exception as e:
        print(f"Error: {e}")
        sys.exit(1)


if __name__ == "__main__":
    arg_parser = argparse.ArgumentParser(description="Decrypts a MP4 init and media segment using CENC encryption.")
    arg_parser.add_argument("--init", help="Path to the init segment file", required=False)
    arg_parser.add_argument("--segment", help="Path to the media segment file", required=False)
    arg_parser.add_argument(
        "--combined_segment", help="Path to the combined init and media segment file", required=False
    )
    arg_parser.add_argument("--key_id", help="Key ID in hexadecimal format", required=True)
    arg_parser.add_argument("--key", help="Key in hexadecimal format", required=True)
    arg_parser.add_argument("--output", help="Path to the output file", required=True)
    args = arg_parser.parse_args()
    cli()