yt-dlp/yt_dlp/mp4_parser.py

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import struct
from typing import Tuple
from io import BytesIO, RawIOBase
class LengthLimiter(RawIOBase):
def __init__(self, r: RawIOBase, size: int):
self.r = r
self.remaining = size
def read(self, sz: int = None) -> bytes:
if self.remaining == 0:
return b''
if sz in (-1, None):
sz = self.remaining
sz = min(sz, self.remaining)
ret = self.r.read(sz)
if ret:
self.remaining -= len(ret)
return ret
def readall(self) -> bytes:
if self.remaining == 0:
return b''
ret = self.read(self.remaining)
if ret:
self.remaining -= len(ret)
return ret
def readable(self) -> bool:
return bool(self.remaining)
def read_harder(r, size):
retry = 0
buf = b''
while len(buf) < size and retry < 3:
ret = r.read(size - len(buf))
if not ret:
retry += 1
continue
retry = 0
buf += ret
return buf
def pack_be32(value: int) -> bytes:
return struct.pack('>I', value)
def pack_be64(value: int) -> bytes:
return struct.pack('>L', value)
def unpack_be32(value: bytes) -> int:
return struct.unpack('>I', value)[0]
def unpack_ver_flags(value: bytes) -> Tuple[int, int]:
ver, up_flag, down_flag = struct.unpack('>BBH', value)
return ver, (up_flag << 16 | down_flag)
def unpack_be64(value: bytes) -> int:
return struct.unpack('>L', value)[0]
# https://github.com/gpac/mp4box.js/blob/4e1bc23724d2603754971abc00c2bd5aede7be60/src/box.js#L13-L40
MP4_CONTAINER_BOXES = ('moov', 'trak', 'edts', 'mdia', 'minf', 'dinf', 'stbl', 'mvex', 'moof', 'traf', 'vttc', 'tref', 'iref', 'mfra', 'meco', 'hnti', 'hinf', 'strk', 'strd', 'sinf', 'rinf', 'schi', 'trgr', 'udta', 'iprp', 'ipco')
def parse_mp4_boxes(r: RawIOBase):
"""
Parses an ISO BMFF (which MP4 follows) and yields its boxes as a sequence.
This does not interpret content of these boxes.
Sequence details:
('atom', b'blablabla'): A box, with content (not container boxes)
('atom', b''): Possibly container box (must check MP4_CONTAINER_BOXES) or really an empty box
(None, 'atom'): End of a container box
Example: Path:
('test', b'123456') /test
('box1', b'') /box1 (start of container box)
('helo', b'abcdef') /box1/helo
('1984', b'1q84') /box1/1984
('http', b'') /box1/http (start of container box)
('keys', b'2022') /box1/http/keys
(None , 'http') /box1/http (end of container box)
('topp', b'1991') /box1/topp
(None , 'box1') /box1 (end of container box)
"""
while True:
size_b = read_harder(r, 4)
if not size_b:
break
type_b = r.read(4)
# 00 00 00 20 is big-endian
box_size = unpack_be32(size_b)
type_s = type_b.decode()
if type_s in MP4_CONTAINER_BOXES:
yield (type_s, b'')
yield from parse_mp4_boxes(LengthLimiter(r, box_size - 8))
yield (None, type_s)
continue
# subtract by 8
full_body = read_harder(r, box_size - 8)
yield (type_s, full_body)
def write_mp4_boxes(w: RawIOBase, box_iter):
"""
Writes an ISO BMFF file from a given sequence to a given writer.
The iterator to be passed must follow parse_mp4_boxes's protocol.
"""
stack = [
(None, w), # parent box, IO
]
for btype, content in box_iter:
if btype in MP4_CONTAINER_BOXES:
bio = BytesIO()
stack.append((btype, bio))
continue
elif btype is None:
assert stack[-1][0] == content
btype, bio = stack.pop()
content = bio.getvalue()
wt = stack[-1][1]
wt.write(pack_be32(len(content) + 8))
wt.write(btype.encode()[:4])
wt.write(content)