diff --git a/ios/OralTrainer.xcodeproj/project.xcworkspace/xcuserdata/liushuming.xcuserdatad/UserInterfaceState.xcuserstate b/ios/OralTrainer.xcodeproj/project.xcworkspace/xcuserdata/liushuming.xcuserdatad/UserInterfaceState.xcuserstate
index 9f45dcd..8f6a294 100644
Binary files a/ios/OralTrainer.xcodeproj/project.xcworkspace/xcuserdata/liushuming.xcuserdatad/UserInterfaceState.xcuserstate and b/ios/OralTrainer.xcodeproj/project.xcworkspace/xcuserdata/liushuming.xcuserdatad/UserInterfaceState.xcuserstate differ
diff --git a/sentence_api/processing.py b/sentence_api/processing.py
index 4082597..efaa675 100644
--- a/sentence_api/processing.py
+++ b/sentence_api/processing.py
@@ -90,8 +90,20 @@ _IOS_VIDEO_CODECS = {"h264", "hevc"}
 _IOS_AUDIO_CODECS = {"aac", "mp3", "ac3", "eac3", "alac"}
 
 
-def _probe_stream_codecs(filepath: Path) -> Tuple[Optional[str], Optional[str]]:
+def _ffprobe_bin() -> Optional[str]:
     ffprobe = shutil.which("ffprobe")
+    if ffprobe:
+        return ffprobe
+    ffmpeg = shutil.which("ffmpeg")
+    if ffmpeg:
+        candidate = str(Path(ffmpeg).with_name("ffprobe"))
+        if Path(candidate).is_file():
+            return candidate
+    return None
+
+
+def _probe_stream_codecs(filepath: Path) -> Tuple[Optional[str], Optional[str]]:
+    ffprobe = _ffprobe_bin()
     if ffprobe is None:
         return None, None
     completed = subprocess.run(
@@ -142,13 +154,9 @@ def _ensure_ios_compatible_media(filepath: Path) -> None:
         return
     ffmpeg = shutil.which("ffmpeg")
     if ffmpeg is None:
-        logger.warning(
-            "ffmpeg not found; skipping iOS-compatible transcode for %s (%s/%s)",
-            filepath.name,
-            video_codec,
-            audio_codec,
+        raise RuntimeError(
+            f"iOS cannot play {video_codec}/{audio_codec}; ffmpeg is required to transcode {filepath.name}"
         )
-        return
     tmp = filepath.with_suffix(".ios_tmp.mp4")
     command = [
         ffmpeg,
@@ -163,7 +171,7 @@ def _ensure_ios_compatible_media(filepath: Path) -> None:
         "-map",
         "0:a:0?",
         "-vf",
-        "scale='min(1920,iw)':-2",
+        r"scale=w=min(1920\,iw):h=-2",
         "-c:v",
         "libx264",
         "-preset",
@@ -190,20 +198,21 @@ def _ensure_ios_compatible_media(filepath: Path) -> None:
     )
     try:
         completed = subprocess.run(command, capture_output=True, text=True, timeout=7200)
-        if completed.returncode == 0 and tmp.is_file() and tmp.stat().st_size > 0:
-            tmp.replace(filepath)
-            logger.info("iOS-compatible transcode finished: %s", filepath.name)
-            return
-        logger.warning(
-            "iOS-compatible transcode failed for %s: rc=%d stderr=%s",
-            filepath.name,
-            completed.returncode,
-            (completed.stderr or "")[-400:],
-        )
-    except (subprocess.TimeoutExpired, OSError) as exc:
-        logger.warning("iOS-compatible transcode error for %s: %s", filepath.name, exc)
-    finally:
+        if completed.returncode != 0 or not tmp.is_file() or tmp.stat().st_size <= 0:
+            message = (completed.stderr or "").strip() or "unknown ffmpeg error"
+            raise RuntimeError(
+                f"Could not transcode {filepath.name} from {video_codec}/{audio_codec} to H.264/AAC: {message[-2000:]}"
+            )
+        tmp.replace(filepath)
+    except Exception:
         tmp.unlink(missing_ok=True)
+        raise
+    video_codec, audio_codec = _probe_stream_codecs(filepath)
+    if _needs_ios_compatible_transcode(video_codec, audio_codec):
+        raise RuntimeError(
+            f"Transcoded {filepath.name} is still not iOS-compatible ({video_codec}/{audio_codec})"
+        )
+    logger.info("iOS-compatible transcode finished: %s", filepath.name)
 
 
 class VideoProcessor: