diff --git a/media_shrinker.py b/media_shrinker.py
index d72a8d5..d0c333a 100644
--- a/media_shrinker.py
+++ b/media_shrinker.py
@@ -1507,9 +1507,11 @@ def _parse_probe_payload(
         raise MediaShrinkerError(f"{source_path} has no audio stream")
 
     format_section = payload.get("format", {})
-    duration = _first_float(
-        audio_stream.get("duration"), format_section.get("duration")
-    )
+    # Prefer the stream duration, but a stream-level "0"/"0.000000" (reported by
+    # some containers) is unusable and must fall back to the format duration.
+    duration = _first_float(audio_stream.get("duration"))
+    if duration <= 0:
+        duration = _first_float(format_section.get("duration"))
     if duration <= 0:
         raise MediaShrinkerError(f"{source_path} has no usable duration")
 
diff --git a/tests/test_media_shrinker.py b/tests/test_media_shrinker.py
index 0ab2397..7c3dc2c 100644
--- a/tests/test_media_shrinker.py
+++ b/tests/test_media_shrinker.py
@@ -238,6 +238,28 @@ def test_parse_probe_payload_uses_known_source_size_without_stat(self) -> None:
 
         self.assertEqual(probe.size_bytes, 123)
 
+    def test_parse_probe_payload_falls_back_to_format_duration_when_stream_is_zero(
+        self,
+    ) -> None:
+        # Real ffprobe output: some containers report a stream-level
+        # "duration": "0.000000" while the true duration lives in the format
+        # section. The stream's unusable zero must not shadow the format value.
+        payload = {
+            "streams": [
+                {
+                    "codec_type": "audio",
+                    "codec_name": "aac",
+                    "duration": "0.000000",
+                    "bit_rate": "128000",
+                }
+            ],
+            "format": {"duration": "123.5", "size": "456"},
+        }
+
+        probe = media_shrinker._parse_probe_payload(payload, Path("stream.mp4"))
+
+        self.assertEqual(probe.duration_seconds, 123.5)
+
 
 class PlanningTests(unittest.TestCase):
     def test_pcm_wav_uses_lossless_flac_first_and_preserves_container_metadata(