feat: add loud-only extraction mode with agate gating

extract.py

@@ -5,6 +5,10 @@ Extracts the first 1.5 minutes of a video into:
   - an audio-only file (no video)
 Output goes into an 'extracted' folder next to this script.
 Requires: ffmpeg installed and on PATH.
+
+Usage:
+    python extract.py           # normal extraction
+    python extract.py loud      # loud-only mode: gate out quiet audio, keep only transients
 """
 
 import subprocess
@@ -13,6 +17,11 @@ import sys
 import shutil
 import json
 
+# ─── Loud mode (pass "loud" as arg or env) ───
+LOUD_MODE = "loud" in sys.argv
+if LOUD_MODE:
+    sys.argv.remove("loud")
+
 # ─── Input / config (config.toml is base config, fallback to hardcoded) ───
 CONFIG_PATH = os.path.join(os.path.dirname(os.path.abspath(__file__)), "config.toml")
 _cfg_inputs = None
@@ -307,12 +316,14 @@ def _parse_loudnorm_json(stderr: str) -> dict | None:
         return None
 
 def extract_audio_loudnorm(input_file: str, duration: int, start_sec: float,
-                           out_path: str, stem: str, stream_idx: int | None = None) -> None:
+                           out_path: str, stem: str, stream_idx: int | None = None,
+                           loud_gate: bool = False) -> None:
     """Two-pass EBU R128 loudnorm extraction: measure then apply."""
     ss_args = ["-ss", str(start_sec)] if start_sec and start_sec != 0 else []
     map_args = ["-map", f"0:a:{stream_idx}"] if stream_idx is not None else []
     base = ["ffmpeg", "-y", *ss_args, "-i", input_file, "-t", str(duration), "-vn", *map_args]
     measure_af = f"loudnorm=I={TARGET_LUFS}:TP={TARGET_TP}:LRA={TARGET_LRA}:print_format=json"
+    gate_filter = ",agate=threshold=0.02:ratio=20:attack=5:release=50" if loud_gate else ""
 
     # ─── Pass 1: measure ───
     print(f"[loudness] {stem}: pass 1/2 measuring…")
@@ -320,7 +331,10 @@ def extract_audio_loudnorm(input_file: str, duration: int, start_sec: float,
     r = subprocess.run(cmd_measure, capture_output=True, text=True)
     if r.returncode != 0:
         print(f"[loudness] {stem}: pass 1 failed ({r.stderr.strip()[-80:]}), falling back to simple extract", file=sys.stderr)
-        cmd_fallback = base + [*AUDIO_CODEC, out_path]
+        if loud_gate:
+            cmd_fallback = base + ["-af", f"agate=threshold=0.02:ratio=20:attack=5:release=50", *AUDIO_CODEC, out_path]
+        else:
+            cmd_fallback = base + [*AUDIO_CODEC, out_path]
         r2 = subprocess.run(cmd_fallback, capture_output=True, text=True)
         if r2.returncode != 0:
             sys.exit(f"ffmpeg (audio) failed:\n{r2.stderr}")
@@ -329,7 +343,10 @@ def extract_audio_loudnorm(input_file: str, duration: int, start_sec: float,
     measured = _parse_loudnorm_json(r.stderr)
     if measured is None:
         print(f"[loudness] {stem}: could not parse measurement, falling back to simple extract", file=sys.stderr)
-        cmd_fallback = base + [*AUDIO_CODEC, out_path]
+        if loud_gate:
+            cmd_fallback = base + ["-af", f"agate=threshold=0.02:ratio=20:attack=5:release=50", *AUDIO_CODEC, out_path]
+        else:
+            cmd_fallback = base + [*AUDIO_CODEC, out_path]
         r2 = subprocess.run(cmd_fallback, capture_output=True, text=True)
         if r2.returncode != 0:
             sys.exit(f"ffmpeg (audio) failed:\n{r2.stderr}")
@@ -346,7 +363,7 @@ def extract_audio_loudnorm(input_file: str, duration: int, start_sec: float,
     print(f"[loudness] {stem}: pass 2/2 applying loudnorm → {TARGET_LUFS} LUFS…")
     apply_af = (f"loudnorm=I={TARGET_LUFS}:TP={TARGET_TP}:LRA={TARGET_LRA}"
                 f":measured_I={mi}:measured_TP={mtp}:measured_LRA={mlra}"
-                f":measured_thresh={mthresh}:offset={offset}:linear=true")
+                f":measured_thresh={mthresh}:offset={offset}:linear=true{gate_filter}")
     cmd_apply = base + ["-af", apply_af, *AUDIO_CODEC, out_path]
     r = subprocess.run(cmd_apply, capture_output=True, text=True)
     if r.returncode != 0:
@@ -470,20 +487,22 @@ for _file_idx, INPUT_FILE in enumerate(INPUT_FILES):
         print(f"[audio: {stem}] skipped (no stream selected)")
     elif NORMALIZE:
         print(f"[audio: {stem}] extracting stream {audio_stream} with two-pass loudnorm…")
-        extract_audio_loudnorm(INPUT_FILE, DURATION, START_SEC, audio_out, stem, stream_idx=audio_stream)
+        extract_audio_loudnorm(INPUT_FILE, DURATION, START_SEC, audio_out, stem,
+                               stream_idx=audio_stream, loud_gate=LOUD_MODE)
     else:
         map_args = ["-map", f"0:a:{audio_stream}"]
-        cmd_audio = [
-            "ffmpeg",
-            "-y",
-            *ss_args,
-            "-i", INPUT_FILE,
-            "-t", str(DURATION),
-            "-vn",              # no video
-            *map_args,          # selected audio stream
-            *AUDIO_CODEC,       # pcm_f32le 48kHz mono, CPU (no GPU equiv.)
-            audio_out
-        ]
+        if LOUD_MODE:
+            cmd_audio = [
+                "ffmpeg", "-y", *ss_args, "-i", INPUT_FILE, "-t", str(DURATION),
+                "-vn", *map_args, "-af",
+                "agate=threshold=0.02:ratio=20:attack=5:release=50",
+                *AUDIO_CODEC, audio_out
+            ]
+        else:
+            cmd_audio = [
+                "ffmpeg", "-y", *ss_args, "-i", INPUT_FILE, "-t", str(DURATION),
+                "-vn", *map_args, *AUDIO_CODEC, audio_out
+            ]
         print(f"[audio: {stem}] running ffmpeg (no normalization)…")
         r = subprocess.run(cmd_audio, capture_output=True, text=True)
         if r.returncode != 0: