Fix audio discontinuity by using output seeking

transcoder/tests/hls_validation/test_audio_boundaries.py

@@ -3,7 +3,9 @@ from __future__ import annotations
 from .hls_utils import fetch_text, parse_media_playlist, probe_segment_timeline
 
 
-def test_audio_segment_100_boundary_is_continuous(master_context: dict, test_config, byte_cache) -> None:
+def test_audio_segment_100_boundary_is_continuous(
+    master_context: dict, test_config, byte_cache
+) -> None:
     if not master_context["audios"]:
         return
 
@@ -48,4 +50,57 @@ def test_audio_segment_100_boundary_is_continuous(master_context: dict, test_con
                     f" delta={delta:.6f}s"
                 )
 
-    assert not failures, "audio discontinuity around lazy head boundary: " + ", ".join(failures)
+    assert not failures, "audio discontinuity around lazy head boundary: " + ", ".join(
+        failures
+    )
+
+
+def test_audio_pts_never_resets_across_lazy_windows(
+    master_context: dict, test_config, byte_cache
+) -> None:
+    if not master_context["audios"]:
+        return
+
+    failures: list[str] = []
+    max_allowed_backward_jump_seconds = 0.25
+
+    for audio in master_context["audios"]:
+        text = fetch_text(
+            audio.url,
+            timeout_seconds=test_config.timeout_seconds,
+            headers=test_config.headers,
+        )
+        playlist = parse_media_playlist(text, audio.url, master_context["client_id"])
+        if not playlist.segment_urls:
+            continue
+
+        total_extinf = 0.0
+        # sample enough segments to cross several lazy windows
+        sample_count = min(len(playlist.segment_urls), 340)
+        for idx in range(sample_count):
+            timeline = probe_segment_timeline(
+                segment_url=playlist.segment_urls[idx],
+                map_url=playlist.map_url,
+                timeout_seconds=test_config.timeout_seconds,
+                byte_cache=byte_cache,
+                headers=test_config.headers,
+            )
+            expected = total_extinf
+            drift = timeline.start - expected
+
+            if drift < -max_allowed_backward_jump_seconds:
+                failures.append(
+                    f"{audio.attrs.get('GROUP-ID', audio.url)} seg={idx}"
+                    f" expected_start~{expected:.3f}s actual={timeline.start:.3f}s"
+                    f" backward_jump={-drift:.3f}s"
+                )
+                break
+
+            if idx < len(playlist.segment_durations):
+                dur = playlist.segment_durations[idx]
+                if dur > 0:
+                    total_extinf += dur
+
+    assert not failures, (
+        "audio timeline reset detected across lazy windows: " + ", ".join(failures)
+    )