wtf how does this work

scripts/extract_ktsl2stbin_opus.py

@@ -0,0 +1,106 @@
+#!/usr/bin/env nix-shell
+#!nix-shell -i python3 -p python3
+import struct
+import sys
+import pathlib
+
+
+def crc32ogg(seq):
+    crc = 0
+    for b in seq:
+        crc ^= b << 24
+        for _ in range(8):
+            crc = (crc << 1) ^ 0x104C11DB7 if crc & 0x80000000 else crc << 1
+    return crc
+
+
+def paginate(sequence: int, content: bytes):
+    # Version, flags, position, serial number, sequence number, checksum, segments, segment table
+    flags = 2 if sequence == 0 else 0
+    page = bytearray(
+        b"OggS"
+        + struct.pack(
+            "<BBQIIIB", 0, flags, 0, 0xACAB1234, sequence, 0, (len(content) // 255) + 1
+        )
+        + (b"\xff" * (len(content) // 255))
+        + bytes([len(content) % 255])
+        + content
+    )
+    struct.pack_into("<I", page, 22, crc32ogg(page))
+    if sequence == 0:
+        print(page)
+    return page
+
+
+def write_opus(ktss: bytes, filename: pathlib.Path):
+    # We only deal with opus
+    if ktss[0x20] != 9:
+        return
+
+    out = filename.open("wb")
+
+    channels = ktss[0x29]
+    (sample_rate, num_samples) = struct.unpack("<II", ktss[0x2C:0x34])
+    (start_offset, data_size) = struct.unpack("<II", ktss[0x40:0x48])
+    # (skip,) = struct.unpack("<I", ktss[0x58:0x5C])
+    skip = 0
+    stream_count = ktss[0x5A]
+    coupled_count = ktss[0x5B]
+    channel_mapping = ktss[0x5C : 0x5C + channels]
+
+    opus_header = (
+        b"OpusHead"
+        + struct.pack(
+            "<BBHIHBBB",
+            1,
+            channels,
+            skip,
+            sample_rate,
+            0,
+            1,
+            stream_count,
+            coupled_count,
+        )
+        + channel_mapping
+    )
+    # Channel mapping is apparently incorrect for 6 channels but I don't care
+    out.write(paginate(0, opus_header))
+
+    comment_header = b"OpusTags\4\0\0\0ktss\0\0\0\0\0\0\0\0"
+    out.write(paginate(1, comment_header))
+
+    # Weird length encoding here, not opus standard
+    sequence = 2
+    offset = start_offset
+    while offset < len(ktss):
+        (packet_len,) = struct.unpack(">I", ktss[offset : offset + 4])
+        out.write(paginate(sequence, ktss[offset + 8 : offset + 8 + packet_len]))
+
+        offset += packet_len + 8
+        sequence += 1
+
+
+# i don't care about efficiency
+data = open(sys.argv[1], "rb").read()
+outdir = pathlib.Path(sys.argv[2])
+
+if data[:4] != b"KTSR":
+    raise Exception("what are you doing")
+
+# there's some more stuff but i don't care, go straight to the entry
+off = 0x40
+idx = 0
+while off < len(data):
+
+    if data[off + 0x40 : off + 0x44] != b"KTSS":
+        raise Exception("oh no offset broken")
+
+    (entry_size,) = struct.unpack("<I", data[off + 4 : off + 8])
+    (size,) = struct.unpack("<I", data[off + 0x44 : off + 0x48])
+
+    ktss = data[off + 0x40 : off + 0x40 + size]
+    write_opus(ktss, outdir / f"{idx}.opus")
+
+    off += entry_size
+    idx += 1
+    print(idx, hex(off))