diff --git a/apply_sync.py b/apply_sync.py
index e9d2ea2..18aa97e 100644
--- a/apply_sync.py
+++ b/apply_sync.py
@@ -159,11 +159,10 @@ def main():
     # Auto-launch verify_sync in full mode
     verify_script = os.path.join(os.path.dirname(os.path.abspath(__file__)), "verify_sync.py")
     if os.path.exists(verify_script):
-        import subprocess as _sp
         verify_cmd = [sys.executable, verify_script, "--config", args.config or "config.toml",
                       "--lag", f"{args.lag:.6f}", "--mode", "full"]
         print(f"Launching verify: {' '.join(verify_cmd)}")
-        _sp.Popen(verify_cmd)
+        subprocess.Popen(verify_cmd)
 
     sys.exit(0)
 
diff --git a/rename_audio.py b/rename_audio.py
index 00a5420..9c1f205 100644
--- a/rename_audio.py
+++ b/rename_audio.py
@@ -25,7 +25,6 @@ import shutil
 import subprocess
 import sys
 import tempfile
-import numpy as np
 
 try:
     import whisper
@@ -195,41 +194,6 @@ def get_lang_name(code: str) -> str:
     return LANG_NAMES.get(code, code.upper())
 
 
-def apply_metadata(file_path: str, stream_idx: int, lang_code_3: str,
-                   title: str, dry_run: bool = True) -> str:
-    """
-    Apply language metadata to a specific audio stream.
-    Returns the ffmpeg command (for display) or runs it.
-    """
-    # Use 3-letter ISO 639-2/B code for MKV
-    meta_key = f"metadata:s:a:{stream_idx}"
-
-    cmd = [
-        "ffmpeg", "-y",
-        "-i", file_path,
-        "-map", "0",
-        "-c", "copy",
-        f"{meta_key}:language={lang_code_3}",
-        f"{meta_key}:title={title}",
-    ]
-
-    if dry_run:
-        return " ".join(cmd)
-
-    # Write to temp file, then replace
-    base, ext = os.path.splitext(file_path)
-    tmp_out = f"{tmp_out_base}{ext}"
-    cmd.append(tmp_out)
-
-    r = subprocess.run(cmd, capture_output=True, timeout=300)
-    if r.returncode != 0:
-        print(f"  ERROR: ffmpeg metadata failed: {r.stderr.decode()[-200:]}", file=sys.stderr)
-        return ""
-
-    # Replace original
-    shutil.move(tmp_out, file_path)
-    return file_path
-
 
 def main():
     ap = argparse.ArgumentParser(description="Detect audio languages via Whisper and set MKV metadata")
diff --git a/sync_audio.py b/sync_audio.py
index d8179df..96a7168 100644
--- a/sync_audio.py
+++ b/sync_audio.py
@@ -15,7 +15,6 @@ Usage:
 from __future__ import annotations
 import os
 import sys
-import math
 from typing import Tuple, Literal
 
 import numpy as np
@@ -120,24 +119,14 @@ def correlate(
             # fftshift to center 0 lag
             corr_t = torch.roll(corr_t, shifts=N // 2)
             corr = corr_t.cpu().numpy()
-            # keep only valid length n centered
-            start = N // 2 - (len(b) - 1)
-            # Actually after roll, we want slice; simpler: use raw without roll and map lag later
-            # Recompute without roll for correct indexing, keep roll for display but fix lag calc
-            # For lag calc we need not shift: peak at N - lag etc. So we use shifted version + offset mapping
-            # To avoid confusion, return shifted corr and map lag accordingly
-            peak_idx = int(np.argmax(np.abs(corr)))
-            # lag = peak_idx - (len(b)-1) - (N//2 - (len(b)-1))? Let's instead use unshifted for lag and shifted for display
-            # Fallback: compute lag from unshifted
+            # compute lag from unshifted correlation for correct indexing
             corr_raw = torch.fft.irfft(R, n=N).cpu().numpy()
             peak_raw = int(np.argmax(np.abs(corr_raw)))
-            # raw layout: lag 0 at 0, positive lag (b delayed) wraps to end
             if peak_raw > N // 2:
                 lag = peak_raw - N
             else:
                 lag = peak_raw
             peak_val = float(np.abs(corr_raw[peak_raw]))
-            # return shifted display corr + lag
             return lag, peak_val, corr
         except Exception as e:
             print(f"torch cuda failed ({e}), falling back cpu", file=sys.stderr)
@@ -156,10 +145,7 @@ def correlate(
     else:
         lag = peak_raw
     peak_val = float(np.abs(corr_raw[peak_raw]))
-    # shifted for display centered at 0
     corr_shifted = np.fft.fftshift(corr_raw)
-    # but we return raw shifted centered? Provide shifted for plotting
-    # For consistency with torch branch we return shifted display array
     return lag, peak_val, corr_shifted
 
 
@@ -170,9 +156,7 @@ def lag_to_seconds(lag_samples: int, sr: int = 48000) -> float:
 def apply_lag_with_silence(wav: np.ndarray, lag_samples: int) -> np.ndarray:
     """
     Apply lag by padding silence at start (no sound for delay).
-    lag >0: b delayed vs a => pad b at start with lag silence to align to a, or trim a.
-    For mux: if lag>0 (b starts later), we need to delay a by lag or提前 b.
-    This helper pads with zeros (silence) at start; negative lag pads the other direction.
+    lag > 0: b delayed vs a. lag < 0: a delayed vs b.
     Caller decides which file to pad.
     """
     if lag_samples == 0:
@@ -200,7 +184,7 @@ def device_info() -> str:
 
 
 if __name__ == "__main__":
-    import argparse, pathlib
+    import argparse
     ap = argparse.ArgumentParser()
     ap.add_argument("a", help="wav A")
     ap.add_argument("b", help="wav B")
diff --git a/sync_audio_test.py b/sync_audio_test.py
index 4447bdd..7f61ed6 100644
--- a/sync_audio_test.py
+++ b/sync_audio_test.py
@@ -13,7 +13,7 @@ Run: make ast  or  .venv/bin/python sync_audio_test.py --config config.toml
 """
 
 from __future__ import annotations
-import os, sys, math, argparse, pathlib
+import os, sys, math, argparse
 import numpy as np
 
 # allow tomllib (py3.11+) with tomli fallback
@@ -31,12 +31,6 @@ except ImportError as e:
     print(e, file=sys.stderr)
     sys.exit(1)
 
-try:
-    import soundfile as sf
-    HAS_SF = True
-except ImportError:
-    HAS_SF = False
-
 try:
     import sounddevice as sd
     HAS_SD = True
@@ -152,15 +146,9 @@ class SyncWindow(QtWidgets.QMainWindow):
 
         # xcorr display — corr is already fftshifted
         N = len(self.corr)
-        # lags in seconds for display
-        total = len(self.a) + len(self.b) - 1
-        n_pow2 = N
         # shifted lags: -N//2 .. N//2-1
         self.corr_lags = np.arange(N) - N//2
         self.corr_lags_sec = self.corr_lags / sr
-        # find peak index in raw (unshifted) for decimation
-        peak_raw_idx = int(np.argmax(np.abs(self.corr)))  # this is fftshifted, peak near center
-        # for decimation we need the index in the shifted array
 
         central = QtWidgets.QWidget()
         self.setCentralWidget(central)
diff --git a/verify_sync.py b/verify_sync.py
index 5712c6a..611ad8c 100644
--- a/verify_sync.py
+++ b/verify_sync.py
@@ -22,7 +22,7 @@ Usage:
 """
 
 from __future__ import annotations
-import os, sys, math, argparse, subprocess, json, shutil, time, threading, tempfile, warnings
+import os, sys, math, argparse, subprocess, json, shutil, threading, tempfile, warnings
 import numpy as np
 
 warnings.filterwarnings("ignore", category=RuntimeWarning, module="pyqtgraph")
@@ -54,12 +54,6 @@ try:
 except ImportError:
     HAS_SD = False
 
-try:
-    import soundfile as sf
-    HAS_SF = True
-except ImportError:
-    HAS_SF = False
-
 from sync_audio import load_wav
 from waveform_cache import cached_load_wav