fix: transcode video for QMediaPlayer and force xcb platform

Makefile

@@ -84,7 +84,7 @@ sync:
 	@if [ -x $(PY) ]; then $(PY) apply_sync.py --config $(CONFIG) --lag $(LAG); else python3 apply_sync.py --config $(CONFIG) --lag $(LAG); fi
 
 verify:
-	@if [ -x $(PY) ]; then QT_QPA_PLATFORM=xcb QT_STYLE_OVERRIDE=Fusion $(PY) verify_sync.py --config $(CONFIG) --lag $(LAG); else QT_QPA_PLATFORM=xcb QT_STYLE_OVERRIDE=Fusion python3 verify_sync.py --config $(CONFIG) --lag $(LAG); fi
+	@if [ -x $(PY) ]; then QT_QPA_PLATFORM=xcb QT_FFMPEG_DECODING_HW_DEVICE_TYPES=vaapi QT_XCB_GL_INTEGRATION=xcb_egl QT_STYLE_OVERRIDE=Fusion $(PY) verify_sync.py --config $(CONFIG) --lag $(LAG); else QT_QPA_PLATFORM=xcb QT_FFMPEG_DECODING_HW_DEVICE_TYPES=vaapi QT_XCB_GL_INTEGRATION=xcb_egl QT_STYLE_OVERRIDE=Fusion python3 verify_sync.py --config $(CONFIG) --lag $(LAG); fi
 
 ast:
 	@AUDIO_A=$$(python3 -c "import tomllib; c=tomllib.load(open('config.toml','rb')); print(c['extract'].get('file_a',''))" 2>/dev/null); \
@@ -100,7 +100,7 @@ ast:
 	else \
 		echo "=> extracted wavs exist ($$OUT/$${STEM_A}_audio.wav, $$OUT/$${STEM_B}_audio.wav), skipping extract"; \
 	fi
-	@if [ -x $(PY) ]; then QT_STYLE_OVERRIDE=Fusion $(PY) sync_audio_test.py --config $(CONFIG); else QT_STYLE_OVERRIDE=Fusion python3 sync_audio_test.py --config $(CONFIG); fi
+	@if [ -x $(PY) ]; then QT_QPA_PLATFORM=xcb QT_FFMPEG_DECODING_HW_DEVICE_TYPES=vaapi QT_XCB_GL_INTEGRATION=xcb_egl QT_STYLE_OVERRIDE=Fusion $(PY) sync_audio_test.py --config $(CONFIG); else QT_QPA_PLATFORM=xcb QT_FFMPEG_DECODING_HW_DEVICE_TYPES=vaapi QT_XCB_GL_INTEGRATION=xcb_egl QT_STYLE_OVERRIDE=Fusion python3 sync_audio_test.py --config $(CONFIG); fi
 
 clean:
 	rm -rf $(VENV) __pycache__ .pytest_cache

verify_sync.py

@@ -27,6 +27,13 @@ import numpy as np
 
 warnings.filterwarnings("ignore", category=RuntimeWarning, module="pyqtgraph")
 
+# Force X11/xcb on Wayland without EGL — QVideoWidget can't render without it
+for k, v in {"QT_QPA_PLATFORM": "xcb",
+             "QT_STYLE_OVERRIDE": "Fusion",
+             "QT_FFMPEG_DECODING_HW_DEVICE_TYPES": "vaapi",
+             "QT_XCB_GL_INTEGRATION": "xcb_egl"}.items():
+    os.environ.setdefault(k, v)
+
 try:
     import tomllib
 except ModuleNotFoundError:
@@ -108,6 +115,28 @@ def extract_audio_from_mkv(mkv_path: str, stream_index: int, out_wav: str, sr: i
         return False
 
 
+def transcode_to_h264_sdr(src: str, dst: str, duration: float = 0) -> bool:
+    """Transcode video to H.264 SDR MP4 for QMediaPlayer compatibility.
+    If duration > 0, only transcode that many seconds."""
+    cmd = ["ffmpeg", "-y", "-i", src]
+    if duration > 0:
+        cmd += ["-t", f"{duration:.3f}"]
+    cmd += [
+        "-map", "0:v:0",
+        "-an",
+        "-c:v", "libx264", "-preset", "ultrafast", "-crf", "20",
+        "-pix_fmt", "yuv420p",
+        "-vf", "scale=trunc(iw/2)*2:trunc(ih/2)*2",
+        "-movflags", "+faststart",
+        dst,
+    ]
+    try:
+        r = subprocess.run(cmd, capture_output=True, timeout=600)
+        return r.returncode == 0 and os.path.exists(dst)
+    except Exception:
+        return False
+
+
 def apply_lag(a: np.ndarray, b: np.ndarray, lag_samples: int) -> tuple[np.ndarray, np.ndarray]:
     if lag_samples >= 0:
         a_out = a[lag_samples:]
@@ -621,6 +650,15 @@ def main():
             print(f"ERROR: wav B not found: {wav_b}", file=sys.stderr); sys.exit(1)
 
         video_path = video_a
+        # In short mode, use the extracted FFV1 video instead of the original HEVC source
+        if args.mode == "short":
+            stem = os.path.splitext(os.path.basename(video_a))[0]
+            extracted_video = os.path.join(out_dir_extract, f"{stem}_video.mkv")
+            if os.path.exists(extracted_video):
+                video_path = extracted_video
+                print(f"Using extracted video: {video_path}")
+            else:
+                print(f"WARNING: extracted video not found ({extracted_video}), using original", file=sys.stderr)
         temp_dir = None
 
     print(f"Mode:    {args.mode}")
@@ -632,6 +670,31 @@ def main():
     app = QtWidgets.QApplication(sys.argv)
     apply_dark_theme(app)
 
+    # Check if QMediaPlayer supports the video codec; only transcode if needed
+    probe = QtMultimedia.QMediaPlayer()
+    probe.setSource(QtCore.QUrl.fromLocalFile(os.path.abspath(video_path)))
+    support = probe.support()
+    del probe
+
+    if support != QtMultimedia.QMediaPlayer.Support.Supported:
+        if not temp_dir:
+            temp_dir = tempfile.mkdtemp(prefix="verify_sync_")
+        preview_path = os.path.join(temp_dir, "preview.mp4")
+        if not os.path.exists(preview_path):
+            transcode_dur = 30.0 if args.mode == "short" else 0
+            print(f"Codec not supported by QMediaPlayer (support={support.name}), "
+                  f"transcoding to H.264 SDR ({'%.1fs' % transcode_dur if transcode_dur else 'full'})...")
+            if not transcode_to_h264_sdr(video_path, preview_path, transcode_dur):
+                print(f"WARNING: transcode failed, using original video (may show black)", file=sys.stderr)
+            else:
+                video_path = preview_path
+                print(f"Preview ready: {preview_path}")
+        else:
+            video_path = preview_path
+            print(f"Using cached preview: {preview_path}")
+    else:
+        print(f"Codec supported by QMediaPlayer, using directly")
+
     w = VerifyWindow(video_path, wav_a, wav_b, sr=sr, lag_sec=lag_sec,
                      mode=args.mode, out_dir=out_dir, temp_dir=temp_dir,
                      volume=volume)