quality preset

sam-tool-tauri/src-tauri/src/settings.rs

@@ -24,6 +24,11 @@ pub struct Settings {
     /// bulk extract (take every Nth frame in range). 1 = no decimation.
     #[serde(default = "default_frame_skip")]
     pub frame_skip: u64,
+    /// Maximum height (in pixels) of the canvas backing store during preview.
+    /// 0 = no cap beyond native resolution. Common presets: 2160 (4K),
+    /// 1440 (2K), 1080, 720, 480. Smaller → less draw cost.
+    #[serde(default)]
+    pub preview_max_height: u32,
 }
 
 fn default_sam_url() -> String {
@@ -58,6 +63,7 @@ impl Default for Settings {
             cache_capacity: default_cache_capacity(),
             hwaccel: String::new(),
             frame_skip: default_frame_skip(),
+            preview_max_height: 0,
         }
     }
 }

sam-tool-tauri/src/components/shell/SettingsModal.tsx

@@ -301,6 +301,31 @@ export function SettingsModal({ open, onClose, onSaved }: Props) {
               />
             </label>
           </div>
+
+          <div className="settings-row">
+            <label>
+              <div className="settings-label">
+                Preview quality
+                <span className="dim"> · caps backing-store height; doesn't affect extracted frames</span>
+              </div>
+              <select
+                value={settings.preview_max_height}
+                onChange={(e) =>
+                  setSettings({
+                    ...settings,
+                    preview_max_height: Number(e.target.value),
+                  })
+                }
+              >
+                <option value={0}>Original (no cap)</option>
+                <option value={2160}>4K — 2160p</option>
+                <option value={1440}>2K — 1440p</option>
+                <option value={1080}>1080p</option>
+                <option value={720}>720p</option>
+                <option value={480}>480p</option>
+              </select>
+            </label>
+          </div>
         </section>
 
         {error && <div className="picker-error">{error}</div>}

sam-tool-tauri/src/index.css

@@ -1606,6 +1606,15 @@ main {
     0 1px 0 rgba(255, 255, 255, 0.04) inset;
 }
 
+/* ExtractMode: canvas-frame must fill the stage at the video's aspect-ratio.
+   We can't rely on the <canvas>'s intrinsic size anymore (its backing store
+   is JS-controlled and capped), so this rule supplies the real display size.
+   The :not(.zoomable) scope leaves AnnotateMode's zoom layout untouched. */
+.canvas-stage:not(.zoomable) .canvas-frame {
+  height: 100%;
+  max-width: 100%;
+}
+
 .canvas-frame canvas {
   width: 100%;
   height: 100%;

sam-tool-tauri/src/modes/ExtractMode.tsx

@@ -28,6 +28,13 @@ export function ExtractMode({ username, settings }: Props) {
   useEffect(() => {
     frameSkipRef.current = Math.max(1, settings?.frame_skip ?? 1);
   }, [settings?.frame_skip]);
+  // Preview-quality cap (in px height; 0 = original). Read per-draw via ref
+  // so a settings change triggers an immediate redraw of the current frame
+  // without rebuilding the playback effect.
+  const previewMaxHRef = useRef<number>(settings?.preview_max_height ?? 0);
+  useEffect(() => {
+    previewMaxHRef.current = settings?.preview_max_height ?? 0;
+  }, [settings?.preview_max_height]);
   const [video, setVideo] = useState<VideoInfo | null>(null);
   const [frameIdx, setFrameIdx] = useState(0);
   const [playing, setPlaying] = useState(false);
@@ -120,20 +127,27 @@ export function ExtractMode({ username, settings }: Props) {
       const ctx = canvas.getContext("2d");
       if (!ctx) return;
 
-      // Backing store = displayed CSS rect × DPR, capped at video native
-      // resolution (anything above is upsampling for no benefit). Halves
-      // drawImage cost on 4K-into-1080p, which is the common slow-system
-      // case. Coords below are in image-pixel space — the transform handles
-      // the mapping to backing pixels, so overlay.ts is unchanged.
+      // Backing store = displayed CSS rect × DPR, capped at video native and
+      // optionally at the user's Preview-quality preset. Halves drawImage
+      // cost on 4K-into-1080p (the common slow-system case). Coords below
+      // are in image-pixel space — the transform maps to backing pixels so
+      // overlay.ts is unchanged.
       const rect = canvas.getBoundingClientRect();
       const dpr = window.devicePixelRatio || 1;
+      let maxW = video.width;
+      let maxH = video.height;
+      const previewMaxH = previewMaxHRef.current;
+      if (previewMaxH > 0 && previewMaxH < video.height) {
+        maxH = previewMaxH;
+        maxW = Math.round(previewMaxH * (video.width / video.height));
+      }
       const targetW = Math.max(
         1,
-        Math.min(video.width, Math.round(rect.width * dpr))
+        Math.min(maxW, Math.round(rect.width * dpr))
       );
       const targetH = Math.max(
         1,
-        Math.min(video.height, Math.round(rect.height * dpr))
+        Math.min(maxH, Math.round(rect.height * dpr))
       );
       if (canvas.width !== targetW) canvas.width = targetW;
       if (canvas.height !== targetH) canvas.height = targetH;
@@ -249,6 +263,17 @@ export function ExtractMode({ username, settings }: Props) {
 
   useEffect(() => clearBitmapCache, [clearBitmapCache]);
 
+  // Live re-render when the preview-quality cap changes so the user sees the
+  // resolution swap immediately on Settings save instead of having to seek.
+  useEffect(() => {
+    const canvas = canvasRef.current;
+    if (!canvas || !video) return;
+    const idx = frameIdxRef.current;
+    const cached = getCachedBitmap(idx);
+    if (cached) drawBitmap(cached, idx);
+    // If not cached, the next pump invocation picks up the new cap naturally.
+  }, [settings?.preview_max_height, video, drawBitmap, getCachedBitmap]);
+
   // Redraw on canvas resize: backing-store is sized from CSS rect × DPR, so
   // a window resize/maximize would otherwise leave the old backing dimensions
   // until the next decode landed. Cheap — just re-runs drawBitmap on the

sam-tool-tauri/src/types.ts

@@ -97,6 +97,8 @@ export interface Settings {
   hwaccel: string;
   /** Decimation factor for playback advancement + bulk extract. 1 = no decimation. */
   frame_skip: number;
+  /** Cap (height in px) on the canvas backing-store during preview. 0 = original. */
+  preview_max_height: number;
 }
 
 export interface SamModelInfo {