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import struct
from typing import Optional
import json
def write_wav_text_chunk(in_path: str, out_path: str, text: str,
fourcc: bytes = b'json', encoding: str = 'utf-8') -> None:
"""
Insert (or replace) a custom RIFF chunk in a WAV file to hold an arbitrary string.
- in_path: source WAV path
- out_path: destination WAV path (can be the same as in_path for in-place write)
- text: the string to store (e.g., JSON)
- fourcc: 4-byte chunk ID; default b'json'
- encoding: encoding for the string payload; default 'utf-8'
Notes:
* Keeps all original chunks as-is; if a chunk with the same fourcc exists,
its payload is replaced; otherwise a new chunk is appended at the end.
* Pads the chunk to even length per RIFF rules.
* Supports standard little-endian RIFF/WAVE (not RF64 or RIFX).
"""
data = open(in_path, 'rb').read()
if len(data) < 12 or data[:4] not in (b'RIFF',) or data[8:12] != b'WAVE':
raise ValueError("Not a standard little-endian RIFF/WAVE file (RF64/RIFX not supported).")
if len(fourcc) != 4 or not all(32 <= b <= 126 for b in fourcc):
raise ValueError("fourcc must be 4 printable ASCII bytes (e.g., b'json').")
payload = text.encode(encoding)
# Parse existing chunks
pos = 12 # after 'RIFF' + size (4+4) and 'WAVE' (4)
n = len(data)
chunks = [] # list[(cid: bytes, payload: bytes)]
while pos + 8 <= n:
cid = data[pos:pos+4]
size = struct.unpack_from('<I', data, pos+4)[0]
start, end = pos + 8, pos + 8 + size
if end > n:
raise ValueError("Corrupt WAV: chunk size exceeds file length.")
chunks.append((cid, data[start:end]))
pos = end + (size & 1) # pad to even
# Replace existing or append new
replaced = False
new_chunks = []
for cid, cdata in chunks:
if cid == fourcc and not replaced:
new_chunks.append((cid, payload))
replaced = True
else:
new_chunks.append((cid, cdata))
if not replaced:
new_chunks.append((fourcc, payload)) # append at the end (often after 'data')
# Rebuild RIFF body
out_parts = [b'WAVE']
for cid, cdata in new_chunks:
out_parts.append(cid)
out_parts.append(struct.pack('<I', len(cdata)))
out_parts.append(cdata)
if len(cdata) & 1:
out_parts.append(b'\x00') # pad to even size
body = b''.join(out_parts)
riff = b'RIFF' + struct.pack('<I', len(body)) + body
with open(out_path, 'wb') as f:
f.write(riff)
def read_wav_text_chunk(path: str, fourcc: bytes = b'json', encoding: str = 'utf-8') -> Optional[str]:
"""
Read and return the string stored in a custom RIFF chunk from a WAV file.
Returns None if the chunk isn't present.
- path: WAV file path
- fourcc: 4-byte chunk ID to look for (default b'json')
- encoding: decoding used for the stored bytes (default 'utf-8')
"""
data = open(path, 'rb').read()
if len(data) < 12 or data[:4] not in (b'RIFF',) or data[8:12] != b'WAVE':
raise ValueError("Not a standard little-endian RIFF/WAVE file (RF64/RIFX not supported).")
if len(fourcc) != 4:
raise ValueError("fourcc must be 4 bytes.")
pos = 12
n = len(data)
while pos + 8 <= n:
cid = data[pos:pos+4]
size = struct.unpack_from('<I', data, pos+4)[0]
start, end = pos + 8, pos + 8 + size
if end > n:
raise ValueError("Corrupt WAV: chunk size exceeds file length.")
if cid == fourcc:
raw = data[start:end]
return raw.decode(encoding, errors='strict')
pos = end + (size & 1)
return None
def save_audio_metadata(path, configs):
write_wav_text_chunk(path, path, json.dumps(configs))
def read_audio_metadata(path):
return json.loads(read_wav_text_chunk(path)) |