fix(silence): keep negative silence_start intervals as split boundaries

media_shrinker.py

@@ -84,8 +84,8 @@
 BITRATE_SAFETY_MARGIN = 0.92
 OPUS_MAX_BITRATE_BPS = 510_000
 OPUS_MIN_REASONABLE_BITRATE_BPS = 16_000
-SILENCE_START_RE = re.compile(r"silence_start:\s*(?P<value>[0-9]+(?:\.[0-9]+)?)")
-SILENCE_END_RE = re.compile(r"silence_end:\s*(?P<value>[0-9]+(?:\.[0-9]+)?)")
+SILENCE_START_RE = re.compile(r"silence_start:\s*(?P<value>-?[0-9]+(?:\.[0-9]+)?)")
+SILENCE_END_RE = re.compile(r"silence_end:\s*(?P<value>-?[0-9]+(?:\.[0-9]+)?)")
 
 
 class MediaShrinkerError(RuntimeError):

tests/test_media_shrinker.py

@@ -915,6 +915,39 @@ def test_parse_silencedetect_intervals_pairs_long_silence_start_and_end(
             ],
         )
 
+    def test_parse_silencedetect_intervals_keeps_negative_start_at_recording_head(
+        self,
+    ) -> None:
+        # ffmpeg back-dates silence_start by the detection window, so a file that
+        # begins in silence reports a slightly negative silence_start. The whole
+        # interval must survive so it can still be used as a split boundary.
+        stderr = """
+        [silencedetect @ 0x1] silence_start: -0.00816327
+        [silencedetect @ 0x1] silence_end: 150.5 | silence_duration: 150.5
+        """
+
+        intervals = parse_silencedetect_intervals(stderr)
+
+        self.assertEqual(
+            intervals,
+            [SilenceInterval(start_seconds=-0.00816327, end_seconds=150.5)],
+        )
+
+    def test_negative_start_silence_still_drives_split_point(self) -> None:
+        # A silence that opens the recording but extends well past the midpoint is
+        # the best split boundary; dropping it forces an unwanted mid-audio cut.
+        intervals = parse_silencedetect_intervals(
+            "[silencedetect @ 0x1] silence_start: -0.008\n"
+            "[silencedetect @ 0x1] silence_end: 150.5 | silence_duration: 150.5\n"
+        )
+        segments = build_segments(
+            duration_seconds=300.0,
+            max_segment_duration_seconds=200.0,
+            silence_intervals=intervals,
+        )
+
+        self.assertEqual(segments[0].duration_seconds, 150.5)
+
 
 class SilenceDetectionTests(unittest.TestCase):
     @patch("media_shrinker.subprocess.run")