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73import shutil
import subprocess
import tempfile
from pathlib import Path
import ffmpeg
import soundfile as sf
def check_ffmpeg() -> None:
if not shutil.which("ffmpeg"):
raise RuntimeError("ffmpeg not found on $PATH")
def build_m4b(
wav_paths: list[Path],
titles: list[str],
output: Path,
*,
book_title: str = "Audiobook",
bitrate: str = "48k",
) -> None:
"""Merge per-chapter WAVs into a single M4B with chapter markers."""
output.parent.mkdir(parents=True, exist_ok=True)
# Build chapter timestamps
cursor = 0
spans: list[tuple[str, int, int]] = []
for wp, t in zip(wav_paths, titles):
dur = int(sf.info(str(wp)).duration * 1000)
spans.append((t, cursor, cursor + dur))
cursor += dur
# Write FFMETADATA1 chapter file
meta = tempfile.NamedTemporaryFile("w", suffix=".txt", delete=False)
meta.write(f";FFMETADATA1\ntitle={book_title}\n\n")
for t, s, e in spans:
meta.write(f"[CHAPTER]\nTIMEBASE=1/1000\nSTART={s}\nEND={e}\ntitle={t}\n\n")
meta.close()
# Write concat file list
concat = tempfile.NamedTemporaryFile("w", suffix=".txt", delete=False)
for wp in wav_paths:
concat.write(f"file '{wp.resolve()}'\n")
concat.close()
try:
stream = ffmpeg.input(concat.name, f="concat", safe=0).audio
stream = stream.filter("loudnorm", I=-16, TP=-1.5, LRA=11)
codec = (
"libfdk_aac"
if "libfdk_aac" in subprocess.getoutput("ffmpeg -encoders")
else "aac"
)
(
ffmpeg.output(
stream,
str(output),
map_metadata=1,
acodec=codec,
audio_bitrate=bitrate,
movflags="+faststart",
)
.global_args("-i", meta.name)
.overwrite_output()
.run(capture_stdout=True, capture_stderr=True)
)
finally:
Path(meta.name).unlink(missing_ok=True)
Path(concat.name).unlink(missing_ok=True)