fmp4utils.py

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"""Utilities to help convert mp4s to fmp4s."""
 
from __future__ import annotations
 
from collections.abc import Generator
from typing import TYPE_CHECKING
 
from homeassistant.exceptions import HomeAssistantError
 
from .core import Orientation
 
if TYPE_CHECKING:
    from io import BufferedIOBase
 
 
def find_box(
    mp4_bytes: bytes, target_type: bytes, box_start: int = 0
) -> Generator[int]:
    """Find location of first box (or sub box if box_start provided) of given type."""
    if box_start == 0:
        index = 0
        box_end = len(mp4_bytes)
    else:
        box_end = box_start + int.from_bytes(
            mp4_bytes[box_start : box_start + 4], byteorder="big"
        )
        index = box_start + 8
    while 1:
        if index > box_end - 8:  # End of box, not found
            break
        box_header = mp4_bytes[index : index + 8]
        if box_header[4:8] == target_type:
            yield index
        index += int.from_bytes(box_header[0:4], byteorder="big")
 
 
def get_codec_string(mp4_bytes: bytes) -> str:
    """Get RFC 6381 codec string."""
    codecs = []
 
    # Find moov
    moov_location = next(find_box(mp4_bytes, b"moov"))
 
    # Find tracks
    for trak_location in find_box(mp4_bytes, b"trak", moov_location):
        # Drill down to media info
        mdia_location = next(find_box(mp4_bytes, b"mdia", trak_location))
        minf_location = next(find_box(mp4_bytes, b"minf", mdia_location))
        stbl_location = next(find_box(mp4_bytes, b"stbl", minf_location))
        stsd_location = next(find_box(mp4_bytes, b"stsd", stbl_location))
 
        # Get stsd box
        stsd_length = int.from_bytes(
            mp4_bytes[stsd_location : stsd_location + 4], byteorder="big"
        )
        stsd_box = mp4_bytes[stsd_location : stsd_location + stsd_length]
 
        # Base Codec
        codec = stsd_box[20:24].decode("utf-8")
 
        # Handle H264
        if (
            codec in ("avc1", "avc2", "avc3", "avc4")
            and stsd_length > 110
            and stsd_box[106:110] == b"avcC"
        ):
            profile = stsd_box[111:112].hex()
            compatibility = stsd_box[112:113].hex()
            # Cap level at 4.1 for compatibility with some Google Cast devices
            level = hex(min(stsd_box[113], 41))[2:]
            codec += "." + profile + compatibility + level
 
        # Handle H265
        elif (
            codec in ("hev1", "hvc1")
            and stsd_length > 110
            and stsd_box[106:110] == b"hvcC"
        ):
            tmp_byte = int.from_bytes(stsd_box[111:112], byteorder="big")
 
            # Profile Space
            codec += "."
            profile_space_map = {0: "", 1: "A", 2: "B", 3: "C"}
            profile_space = tmp_byte >> 6
            codec += profile_space_map[profile_space]
            general_profile_idc = tmp_byte & 31
            codec += str(general_profile_idc)
 
            # Compatibility
            codec += "."
            general_profile_compatibility = int.from_bytes(
                stsd_box[112:116], byteorder="big"
            )
            reverse = 0
            for i in range(32):
                reverse |= general_profile_compatibility & 1
                if i == 31:
                    break
                reverse <<= 1
                general_profile_compatibility >>= 1
            codec += hex(reverse)[2:]
 
            # Tier Flag
            if (tmp_byte & 32) >> 5 == 0:
                codec += ".L"
            else:
                codec += ".H"
            codec += str(int.from_bytes(stsd_box[122:123], byteorder="big"))
 
            # Constraint String
            has_byte = False
            constraint_string = ""
            for i in range(121, 115, -1):
                gci = int.from_bytes(stsd_box[i : i + 1], byteorder="big")
                if gci or has_byte:
                    constraint_string = "." + hex(gci)[2:] + constraint_string
                    has_byte = True
            codec += constraint_string
 
        # Handle Audio
        elif codec == "mp4a":
            oti = None
            dsi = None
 
            # Parse ES Descriptors
            oti_loc = stsd_box.find(b"\x04\x80\x80\x80")
            if oti_loc > 0:
                oti = stsd_box[oti_loc + 5 : oti_loc + 6].hex()
                codec += f".{oti}"
 
            dsi_loc = stsd_box.find(b"\x05\x80\x80\x80")
            if dsi_loc > 0:
                dsi_length = int.from_bytes(
                    stsd_box[dsi_loc + 4 : dsi_loc + 5], byteorder="big"
                )
                dsi_data = stsd_box[dsi_loc + 5 : dsi_loc + 5 + dsi_length]
                dsi0 = int.from_bytes(dsi_data[0:1], byteorder="big")
                dsi = (dsi0 & 248) >> 3
                if dsi == 31 and len(dsi_data) >= 2:
                    dsi1 = int.from_bytes(dsi_data[1:2], byteorder="big")
                    dsi = 32 + ((dsi0 & 7) << 3) + ((dsi1 & 224) >> 5)
                codec += f".{dsi}"
 
        codecs.append(codec)
 
    return ",".join(codecs)
 
 
def find_moov(mp4_io: BufferedIOBase) -> int:
    """Find location of moov atom in a BufferedIOBase mp4."""
    index = 0
    # Ruff doesn't understand this loop - the exception is always raised at the end
    while 1:  # noqa: RET503
        mp4_io.seek(index)
        box_header = mp4_io.read(8)
        if len(box_header) != 8 or box_header[0:4] == b"\x00\x00\x00\x00":
            raise HomeAssistantError("moov atom not found")
        if box_header[4:8] == b"moov":
            return index
        index += int.from_bytes(box_header[0:4], byteorder="big")
 
 
def read_init(bytes_io: BufferedIOBase) -> bytes:
    """Read the init from a mp4 file."""
    moov_loc = find_moov(bytes_io)
    bytes_io.seek(moov_loc)
    moov_len = int.from_bytes(bytes_io.read(4), byteorder="big")
    bytes_io.seek(0)
    return bytes_io.read(moov_loc + moov_len)
 
 
ZERO32 = b"\x00\x00\x00\x00"
ONE32 = b"\x00\x01\x00\x00"
NEGONE32 = b"\xff\xff\x00\x00"
XYW_ROW = ZERO32 + ZERO32 + b"\x40\x00\x00\x00"
ROTATE_RIGHT = (ZERO32 + ONE32 + ZERO32) + (NEGONE32 + ZERO32 + ZERO32)
ROTATE_LEFT = (ZERO32 + NEGONE32 + ZERO32) + (ONE32 + ZERO32 + ZERO32)
ROTATE_180 = (NEGONE32 + ZERO32 + ZERO32) + (ZERO32 + NEGONE32 + ZERO32)
MIRROR = (NEGONE32 + ZERO32 + ZERO32) + (ZERO32 + ONE32 + ZERO32)
FLIP = (ONE32 + ZERO32 + ZERO32) + (ZERO32 + NEGONE32 + ZERO32)
# The two below do not seem to get applied properly
ROTATE_LEFT_FLIP = (ZERO32 + NEGONE32 + ZERO32) + (NEGONE32 + ZERO32 + ZERO32)
ROTATE_RIGHT_FLIP = (ZERO32 + ONE32 + ZERO32) + (ONE32 + ZERO32 + ZERO32)
 
TRANSFORM_MATRIX_TOP = (
    # The index into this tuple corresponds to the EXIF orientation tag
    # Only index values of 2 through 8 are used
    # The first two entries are just to keep everything aligned
    b"",  # 0
    b"",  # 1
    MIRROR,  # 2
    ROTATE_180,  # 3
    FLIP,  # 4
    ROTATE_LEFT_FLIP,  # 5
    ROTATE_LEFT,  # 6
    ROTATE_RIGHT_FLIP,  # 7
    ROTATE_RIGHT,  # 8
)
 
 
def transform_init(init: bytes, orientation: Orientation) -> bytes:
    """Change the transformation matrix in the header."""
    if orientation == Orientation.NO_TRANSFORM:
        return init
    # Find moov
    moov_location = next(find_box(init, b"moov"))
    mvhd_location = next(find_box(init, b"trak", moov_location))
    tkhd_location = next(find_box(init, b"tkhd", mvhd_location))
    tkhd_length = int.from_bytes(
        init[tkhd_location : tkhd_location + 4], byteorder="big"
    )
    return (
        init[: tkhd_location + tkhd_length - 44]
        + TRANSFORM_MATRIX_TOP[orientation]
        + XYW_ROW
        + init[tkhd_location + tkhd_length - 8 :]
    )