Validate frame-accurate seeking with python-mpv (build order step 1)

Confirms single-frame stepping is reliable: monotonic frame counter across steps, and the synthetic clip's 1-frame flash event lands on exactly one frame with clean neighbors. Also documents/works around three environment quirks hit along the way: locally-built libmpv not in ldconfig's cache, QApplication resetting LC_NUMERIC and breaking libmpv's locale requirement, and the playback-restart event not firing reliably after frame-step (switched to polling estimated_frame_number).
2026-07-26 00:37:42 +02:00
parent 7584970498
commit 91390f751d
5 changed files with 220 additions and 0 deletions
@@ -0,0 +1,34 @@
+import locale
+locale.setlocale(locale.LC_NUMERIC, "C")
+import mpv
+import time
+from pathlib import Path
+
+CLIP = str(Path(__file__).resolve().parent.parent / "test_media" / "sync_test_INSYNC.mp4")
+
+m = mpv.MPV(hr_seek="yes", hr_seek_framedrop="no", keep_open="yes", pause=True, vo="null")
+
+events_seen = []
+@m.event_callback('playback-restart', 'seek', 'file-loaded')
+def cb(evt):
+    events_seen.append(str(evt))
+
+m.play(CLIP)
+m.wait_for_property("duration", timeout=10)
+m.pause = True
+print("loaded, duration=", m.duration, "fps=", m.container_fps)
+
+m.seek(4.9, reference="absolute", precision="exact")
+time.sleep(0.5)
+print("after seek: time_pos=", m.time_pos, "frame=", m.estimated_frame_number)
+
+for i in range(5):
+    before = m.time_pos
+    try:
+        with m.prepare_and_wait_for_event('playback-restart', timeout=2.0):
+            m.command('frame-step')
+        print(f"step {i}: OK via event, time_pos={m.time_pos} frame={m.estimated_frame_number}")
+    except TimeoutError:
+        print(f"step {i}: TIMEOUT waiting for playback-restart, time_pos={m.time_pos} frame={m.estimated_frame_number} (before={before})")
+
+m.terminate()
@@ -0,0 +1,62 @@
+"""Standalone validation harness for build-order step 1: confirm python-mpv
+gives frame-accurate seeking before any of the rest of the UI is built.
+
+Steps frame-by-frame across the known flash event in the synthetic test clip
+(white flash at t=5.000s, frame 150 @ 30fps) and dumps a screenshot + reported
+position/frame-number per step, so the results can be inspected directly
+instead of trusted on faith.
+"""
+import sys
+import time
+from pathlib import Path
+
+from PyQt6.QtWidgets import QApplication
+
+sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
+from player_widget import PlayerWidget
+
+CLIP = str(Path(__file__).resolve().parent.parent / "test_media" / "sync_test_INSYNC.mp4")
+OUT_DIR = Path(__file__).resolve().parent.parent / "test_media" / "seek_validation"
+
+
+def main():
+    OUT_DIR.mkdir(exist_ok=True)
+    app = QApplication(sys.argv)
+
+    w = PlayerWidget()
+    w.resize(640, 480)
+    w.show()
+    app.processEvents()
+
+    w.load(CLIP)
+    app.processEvents()
+    print(f"fps reported by mpv: {w.fps()}")
+
+    # Land a few frames before the flash (frame 150 == t=5.000s), then
+    # single-step across it.
+    w.seek(4.900)
+    app.processEvents()
+    time.sleep(0.2)
+    app.processEvents()
+
+    results = []
+    for i in range(8):
+        pos = w.get_position()
+        frame = w.get_estimated_frame()
+        shot = OUT_DIR / f"step_{i:02d}_frame{frame}.png"
+        w.screenshot(str(shot))
+        results.append((i, pos, frame, shot.name))
+        print(f"step {i}: time_pos={pos:.4f}s estimated_frame={frame} -> {shot.name}")
+        w.step_frame(1)
+        app.processEvents()
+
+    w.shutdown()
+
+    print("\nExpected: flash frame is frame index 150 (t=5.000-5.033s).")
+    print("Check the dumped PNGs in test_media/seek_validation/ to confirm")
+    print("exactly one frame is white/bright and it lines up with the")
+    print("reported frame number close to 150.")
+
+
+if __name__ == "__main__":
+    main()