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124 lines
3.3 KiB
Python
124 lines
3.3 KiB
Python
"""Split AV1 low-overhead OBU streams into temporal units."""
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from __future__ import annotations
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OBU_SEQUENCE_HEADER = 1
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OBU_TEMPORAL_DELIMITER = 2
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def _leb128(data: bytes, i: int) -> tuple[int, int] | None:
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n = len(data)
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result = 0
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shift = 0
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while i < n:
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byte = data[i]
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i += 1
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result |= (byte & 0x7F) << shift
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if (byte & 0x80) == 0:
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return result, i
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shift += 7
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if shift > 56:
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return None
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return None
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def parse_obus(data: bytes) -> list[tuple[int, int, int]]:
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"""Return (type, start, end) for each complete OBU. Empty if malformed."""
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out: list[tuple[int, int, int]] = []
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i = 0
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n = len(data)
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while i < n:
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start = i
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hdr = data[i]
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i += 1
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if hdr & 0x80:
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return []
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obu_type = (hdr >> 3) & 0x0F
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has_ext = (hdr & 0x04) != 0
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has_size = (hdr & 0x02) != 0
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if has_ext:
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if i >= n:
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return []
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i += 1
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if has_size:
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leb = _leb128(data, i)
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if leb is None:
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return []
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size, i = leb
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end = i + size
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if end > n:
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return []
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i = end
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else:
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i = n
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out.append((obu_type, start, i))
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return out
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def is_keyframe(tu: bytes) -> bool:
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return any(t == OBU_SEQUENCE_HEADER for t, _s, _e in parse_obus(tu))
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class Av1TuSplitter:
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"""Feed obu-stream bytes; yield complete temporal units."""
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def __init__(self) -> None:
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self._buf = bytearray()
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def push(self, data: bytes) -> list[bytes]:
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if data:
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self._buf.extend(data)
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out: list[bytes] = []
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buf = self._buf
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while True:
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n = len(buf)
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if n < 1:
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break
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i = 0
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tu_end = -1
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saw_coded = False
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ok = True
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while i < n:
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start = i
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hdr = buf[i]
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i += 1
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if hdr & 0x80:
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ok = False
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break
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obu_type = (hdr >> 3) & 0x0F
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has_ext = (hdr & 0x04) != 0
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has_size = (hdr & 0x02) != 0
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if has_ext:
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if i >= n:
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ok = False
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break
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i += 1
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if has_size:
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leb = _leb128(bytes(buf), i)
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if leb is None:
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ok = False
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break
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size, i = leb
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if i + size > n:
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ok = False
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break
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i = i + size
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else:
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ok = False
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break
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if obu_type == OBU_TEMPORAL_DELIMITER and saw_coded:
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tu_end = start
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break
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if obu_type != OBU_TEMPORAL_DELIMITER:
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saw_coded = True
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if not ok:
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if n > 2_000_000:
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del buf[: n - 16]
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break
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if tu_end < 0:
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break
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tu = bytes(buf[:tu_end])
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if tu:
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out.append(tu)
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del buf[:tu_end]
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return out
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