diff --git a/frontend/src/App.tsx b/frontend/src/App.tsx
index 5a10ea5..e077cc4 100644
--- a/frontend/src/App.tsx
+++ b/frontend/src/App.tsx
@@ -21,7 +21,7 @@ import { first, map } from 'rxjs/operators';
 const thumbnailWidth = 177;
 const thumbnailHeight = 100;
 
-const initialViewportSeconds = 10;
+const initialViewportCanvasPixels = 100;
 
 const apiURL = process.env.REACT_APP_API_URL || 'http://localhost:8888';
 
@@ -147,7 +147,8 @@ function App(): JSX.Element {
     }
 
     const numFrames = Math.min(
-      mediaSet.audioSampleRate * initialViewportSeconds,
+      Math.round(mediaSet.audioFrames / CanvasLogicalWidth) *
+        initialViewportCanvasPixels,
       mediaSet.audioFrames
     );
 
diff --git a/frontend/src/HudCanvas.tsx b/frontend/src/HudCanvas.tsx
new file mode 100644
index 0000000..d9a1229
--- /dev/null
+++ b/frontend/src/HudCanvas.tsx
@@ -0,0 +1,289 @@
+import { useState, useEffect, useRef, MouseEvent } from 'react';
+import { VideoPosition } from './App';
+
+interface Props {
+  width: number;
+  height: number;
+  zIndex: number;
+  position: VideoPosition;
+  selection: Selection;
+  onSelectionChange: (selection: Selection) => void;
+}
+
+enum Mode {
+  Normal,
+  Selecting,
+  Dragging,
+  ResizingStart,
+  ResizingEnd,
+}
+
+enum HoverState {
+  Normal,
+  OverSelectionStart,
+  OverSelectionEnd,
+  OverSelection,
+}
+
+export interface Selection {
+  start: number;
+  end: number;
+}
+
+const emptySelection: Selection = { start: 0, end: 0 };
+
+export const HudCanvas: React.FC<Props> = ({
+  width,
+  height,
+  zIndex,
+  position,
+  selection,
+  onSelectionChange,
+}: Props) => {
+  // selection and newSelection are in canvas logical pixels:
+  const [newSelection, setNewSelection] = useState({
+    ...emptySelection,
+  });
+  const [mode, setMode] = useState(Mode.Normal);
+  const [hoverState, setHoverState] = useState(HoverState.Normal);
+  const [cursor, setCursor] = useState('auto');
+
+  const canvasRef = useRef<HTMLCanvasElement>(null);
+  const moveOffsetX = useRef(0);
+
+  // side effects
+
+  // handle global mouse up
+  useEffect(() => {
+    window.addEventListener('mouseup', handleMouseUp);
+    return () => {
+      window.removeEventListener('mouseup', handleMouseUp);
+    };
+  }, [mode, newSelection]);
+
+  // draw the overview HUD
+  useEffect(() => {
+    requestAnimationFrame(() => {
+      const canvas = canvasRef.current;
+      if (canvas == null) {
+        console.error('no hud canvas ref available');
+        return;
+      }
+      const ctx = canvas.getContext('2d');
+      if (ctx == null) {
+        console.error('no hud 2d context available');
+        return;
+      }
+      ctx.clearRect(0, 0, canvas.width, canvas.height);
+
+      // draw selection
+
+      let currentSelection: Selection;
+      if (
+        mode == Mode.Selecting ||
+        mode == Mode.Dragging ||
+        mode == Mode.ResizingStart ||
+        mode == Mode.ResizingEnd
+      ) {
+        currentSelection = newSelection;
+      } else {
+        currentSelection = selection;
+      }
+
+      ctx.beginPath();
+      ctx.strokeStyle = 'red';
+      ctx.lineWidth = 4;
+      const alpha = hoverState == HoverState.OverSelection ? '0.15' : '0.13';
+      ctx.fillStyle = `rgba(255, 255, 255, ${alpha})`;
+      ctx.rect(
+        currentSelection.start,
+        2,
+        currentSelection.end - currentSelection.start,
+        canvas.height - 10
+      );
+      ctx.fill();
+      ctx.stroke();
+
+      // draw position marker
+
+      const markerX = canvas.width * (position.percent / 100);
+      ctx.beginPath();
+      ctx.moveTo(markerX, 0);
+      ctx.lineWidth = 4;
+      ctx.lineTo(markerX, canvas.height - 4);
+      ctx.stroke();
+    });
+  }, [selection, newSelection, position]);
+
+  // handlers
+
+  const hoverOffset = 10;
+
+  const isHoveringSelectionStart = (x: number): boolean => {
+    return (
+      x > selection.start - hoverOffset && x < selection.start + hoverOffset
+    );
+  };
+
+  const isHoveringSelectionEnd = (x: number): boolean => {
+    return x > selection.end - hoverOffset && x < selection.end + hoverOffset;
+  };
+
+  const isHoveringSelection = (x: number): boolean => {
+    return x >= selection.start && x <= selection.end;
+  };
+
+  const getCanvasX = (evt: MouseEvent<HTMLCanvasElement>): number => {
+    const rect = evt.currentTarget.getBoundingClientRect();
+    const x = Math.round(((evt.clientX - rect.left) / rect.width) * width);
+    return constrainXToCanvas(x);
+  };
+
+  const constrainXToCanvas = (x: number): number => {
+    if (x < 0) {
+      return 0;
+    }
+    if (x > width) {
+      return width;
+    }
+    return x;
+  };
+
+  const handleMouseDown = (evt: MouseEvent<HTMLCanvasElement>) => {
+    if (mode != Mode.Normal) {
+      return;
+    }
+
+    const x = getCanvasX(evt);
+
+    if (isHoveringSelectionStart(x)) {
+      setMode(Mode.ResizingStart);
+      moveOffsetX.current = x;
+    } else if (isHoveringSelectionEnd(x)) {
+      setMode(Mode.ResizingEnd);
+      moveOffsetX.current = x;
+    } else if (isHoveringSelection(x)) {
+      setMode(Mode.Dragging);
+      setCursor('pointer');
+      moveOffsetX.current = x;
+    } else {
+      setMode(Mode.Selecting);
+      setCursor('col-resize');
+      moveOffsetX.current = x;
+      setNewSelection({ start: x, end: x });
+    }
+  };
+
+  const handleMouseMove = (evt: MouseEvent<HTMLCanvasElement>) => {
+    const x = getCanvasX(evt);
+
+    switch (mode) {
+      case Mode.Normal: {
+        if (isHoveringSelectionStart(x)) {
+          setHoverState(HoverState.OverSelectionStart);
+          setCursor('col-resize');
+        } else if (isHoveringSelectionEnd(x)) {
+          setHoverState(HoverState.OverSelectionEnd);
+          setCursor('col-resize');
+        } else if (isHoveringSelection(x)) {
+          setHoverState(HoverState.OverSelection);
+          setCursor('pointer');
+        } else {
+          setCursor('auto');
+        }
+        break;
+      }
+      case Mode.ResizingStart: {
+        const diff = x - moveOffsetX.current;
+        const start = constrainXToCanvas(selection.start + diff);
+
+        if (start > selection.end) {
+          setNewSelection({ start: selection.end, end: start });
+          break;
+        }
+
+        setNewSelection({ ...newSelection, start: start });
+        break;
+      }
+      case Mode.ResizingEnd: {
+        const diff = x - moveOffsetX.current;
+        const start = constrainXToCanvas(selection.end + diff);
+
+        if (start < selection.start) {
+          setNewSelection({ start: Math.max(0, start), end: selection.start });
+          break;
+        }
+
+        setNewSelection({ ...newSelection, end: start });
+        break;
+      }
+      case Mode.Dragging: {
+        const diff = x - moveOffsetX.current;
+        const selectionWidth = selection.end - selection.start;
+        let start = Math.max(0, selection.start + diff);
+        let end = start + selectionWidth;
+        if (end > width) {
+          end = width;
+          start = end - selectionWidth;
+        }
+
+        setNewSelection({ start: start, end: end });
+        break;
+      }
+      case Mode.Selecting: {
+        if (x < moveOffsetX.current) {
+          setNewSelection({
+            start: x,
+            end: moveOffsetX.current,
+          });
+        } else {
+          setNewSelection({ start: moveOffsetX.current, end: x });
+        }
+        break;
+      }
+    }
+  };
+
+  const handleMouseUp = () => {
+    if (mode == Mode.Normal) {
+      return;
+    }
+
+    setMode(Mode.Normal);
+    setCursor('auto');
+
+    if (newSelection.start == newSelection.end) {
+      setNewSelection({ start: 0, end: 0 });
+      return;
+    }
+
+    onSelectionChange({ ...newSelection });
+  };
+
+  const handleMouseLeave = (_evt: MouseEvent<HTMLCanvasElement>) => {
+    setHoverState(HoverState.Normal);
+  };
+
+  const canvasStyles = {
+    display: 'block',
+    position: 'absolute',
+    width: '100%',
+    height: '100%',
+    zIndex: zIndex,
+    cursor: cursor,
+  } as React.CSSProperties;
+
+  return (
+    <>
+      <canvas
+        ref={canvasRef}
+        width={width}
+        height={height}
+        style={canvasStyles}
+        onMouseDown={handleMouseDown}
+        onMouseMove={handleMouseMove}
+        onMouseLeave={handleMouseLeave}
+      ></canvas>
+    </>
+  );
+};
diff --git a/frontend/src/Overview.tsx b/frontend/src/Overview.tsx
index 61dd332..1239fe8 100644
--- a/frontend/src/Overview.tsx
+++ b/frontend/src/Overview.tsx
@@ -1,7 +1,8 @@
-import { useState, useEffect, useRef, MouseEvent } from 'react';
+import { useState, useEffect, useCallback } from 'react';
 import { MediaSet } from './generated/media_set';
 import { Frames, VideoPosition } from './App';
 import { WaveformCanvas } from './WaveformCanvas';
+import { HudCanvas } from './HudCanvas';
 import { Observable } from 'rxjs';
 
 export interface Selection {
@@ -16,29 +17,12 @@ interface Props {
   offsetPixels: number;
   position: VideoPosition;
   viewport: Frames;
-  onSelectionChange: (selection: Frames) => void;
-}
-
-enum Mode {
-  Normal,
-  Selecting,
-  Dragging,
-  ResizingStart,
-  ResizingEnd,
-}
-
-enum HoverState {
-  Normal,
-  OverSelectionStart,
-  OverSelectionEnd,
-  OverSelection,
+  onSelectionChange: (selection: Selection) => void;
 }
 
 export const CanvasLogicalWidth = 2_000;
 export const CanvasLogicalHeight = 500;
 
-const emptySelection = { start: 0, end: 0 };
-
 export const Overview: React.FC<Props> = ({
   peaks,
   mediaSet,
@@ -48,36 +32,13 @@ export const Overview: React.FC<Props> = ({
   viewport,
   onSelectionChange,
 }: Props) => {
-  const hudCanvasRef = useRef<HTMLCanvasElement>(null);
-  const [mode, setMode] = useState(Mode.Normal);
-  const [hoverState, setHoverState] = useState(HoverState.Normal);
-  const [cursor, setCursor] = useState('auto');
-
-  // selection and newSelection relate to canvas logical pixels:
-  const [selection, setSelection] = useState({ ...emptySelection });
-  const [newSelection, setNewSelection] = useState({
-    ...emptySelection,
-  });
-
-  const moveOffsetX = useRef(0);
+  const [selectedPixels, setSelectedPixels] = useState({ start: 0, end: 0 });
 
   // side effects
 
-  // handle global mouse up.
+  // convert viewport from frames to canvas pixels.
   useEffect(() => {
-    window.addEventListener('mouseup', handleMouseUp);
-    return () => {
-      window.removeEventListener('mouseup', handleMouseUp);
-    };
-  }, [mode, newSelection]);
-
-  // set selection state on viewport change
-  useEffect(() => {
-    if (mediaSet == null) {
-      return;
-    }
-
-    setSelection({
+    setSelectedPixels({
       start: Math.round(
         (viewport.start / mediaSet.audioFrames) * CanvasLogicalWidth
       ),
@@ -85,235 +46,20 @@ export const Overview: React.FC<Props> = ({
         (viewport.end / mediaSet.audioFrames) * CanvasLogicalWidth
       ),
     });
-  }, [mediaSet, viewport]);
-
-  // load peaks on mediaset change
-  useEffect(() => {
-    (async function () {
-      if (mediaSet == null) {
-        return;
-      }
-      const canvas = hudCanvasRef.current;
-      if (canvas == null) {
-        console.error('no hud canvas ref available');
-        return;
-      }
-      const ctx = canvas.getContext('2d');
-      if (ctx == null) {
-        console.error('no hud 2d context available');
-        return;
-      }
-    })();
-  }, [mediaSet]);
-
-  // draw the overview HUD
-  useEffect(() => {
-    requestAnimationFrame(() => {
-      const canvas = hudCanvasRef.current;
-      if (canvas == null) {
-        console.error('no hud canvas ref available');
-        return;
-      }
-      const ctx = canvas.getContext('2d');
-      if (ctx == null) {
-        console.error('no hud 2d context available');
-        return;
-      }
-      ctx.clearRect(0, 0, canvas.width, canvas.height);
-
-      // draw selection
-
-      let currentSelection: Selection;
-      if (
-        mode == Mode.Selecting ||
-        mode == Mode.Dragging ||
-        mode == Mode.ResizingStart ||
-        mode == Mode.ResizingEnd
-      ) {
-        currentSelection = newSelection;
-      } else {
-        currentSelection = selection;
-      }
-
-      ctx.beginPath();
-      ctx.strokeStyle = 'red';
-      ctx.lineWidth = 4;
-      const alpha = hoverState == HoverState.OverSelection ? '0.15' : '0.13';
-      ctx.fillStyle = `rgba(255, 255, 255, ${alpha})`;
-      ctx.rect(
-        currentSelection.start,
-        2,
-        currentSelection.end - currentSelection.start,
-        canvas.height - 10
-      );
-      ctx.fill();
-      ctx.stroke();
-
-      // draw position marker
-
-      const markerX = canvas.width * (position.percent / 100);
-      ctx.beginPath();
-      ctx.moveTo(markerX, 0);
-      ctx.lineWidth = 4;
-      ctx.lineTo(markerX, canvas.height - 4);
-      ctx.stroke();
-    });
-  }, [mediaSet, selection, newSelection, position]);
+  }, [viewport, mediaSet]);
 
   // handlers
 
-  const hoverOffset = 10;
-
-  const isHoveringSelectionStart = (x: number): boolean => {
-    return (
-      x > selection.start - hoverOffset && x < selection.start + hoverOffset
-    );
-  };
-
-  const isHoveringSelectionEnd = (x: number): boolean => {
-    return x > selection.end - hoverOffset && x < selection.end + hoverOffset;
-  };
-
-  const isHoveringSelection = (x: number): boolean => {
-    return x >= selection.start && x <= selection.end;
-  };
-
-  const getCanvasX = (evt: MouseEvent<HTMLCanvasElement>): number => {
-    const rect = evt.currentTarget.getBoundingClientRect();
-    const x = Math.round(
-      ((evt.clientX - rect.left) / rect.width) * CanvasLogicalWidth
-    );
-    return constrainXToCanvas(x);
-  };
-
-  const constrainXToCanvas = (x: number): number => {
-    if (x < 0) {
-      return 0;
-    }
-    if (x > CanvasLogicalWidth) {
-      return CanvasLogicalWidth;
-    }
-    return x;
-  };
-
-  const handleMouseDown = (evt: MouseEvent<HTMLCanvasElement>) => {
-    if (mode != Mode.Normal) {
-      return;
-    }
-
-    const x = getCanvasX(evt);
-
-    if (isHoveringSelectionStart(x)) {
-      setMode(Mode.ResizingStart);
-      moveOffsetX.current = x;
-      return;
-    } else if (isHoveringSelectionEnd(x)) {
-      setMode(Mode.ResizingEnd);
-      moveOffsetX.current = x;
-      return;
-    } else if (isHoveringSelection(x)) {
-      setMode(Mode.Dragging);
-      setCursor('pointer');
-      moveOffsetX.current = x;
-      return;
-    }
-
-    setMode(Mode.Selecting);
-    setCursor('col-resize');
-    moveOffsetX.current = x;
-    setNewSelection({ start: x, end: x });
-  };
-
-  const handleMouseMove = (evt: MouseEvent<HTMLCanvasElement>) => {
-    const x = getCanvasX(evt);
-
-    switch (mode) {
-      case Mode.Normal: {
-        if (isHoveringSelectionStart(x)) {
-          setHoverState(HoverState.OverSelectionStart);
-          setCursor('col-resize');
-        } else if (isHoveringSelectionEnd(x)) {
-          setHoverState(HoverState.OverSelectionEnd);
-          setCursor('col-resize');
-        } else if (isHoveringSelection(x)) {
-          setHoverState(HoverState.OverSelection);
-          setCursor('pointer');
-        } else {
-          setCursor('auto');
-        }
-        break;
-      }
-      case Mode.ResizingStart: {
-        const diff = x - moveOffsetX.current;
-        const start = constrainXToCanvas(selection.start + diff);
-
-        if (start > selection.end) {
-          setNewSelection({ start: selection.end, end: start });
-          break;
-        }
-
-        setNewSelection({ ...newSelection, start: start });
-        break;
-      }
-      case Mode.ResizingEnd: {
-        const diff = x - moveOffsetX.current;
-        const start = constrainXToCanvas(selection.end + diff);
-
-        if (start < selection.start) {
-          setNewSelection({ start: Math.max(0, start), end: selection.start });
-          break;
-        }
-
-        setNewSelection({ ...newSelection, end: start });
-        break;
-      }
-      case Mode.Dragging: {
-        const diff = x - moveOffsetX.current;
-        const width = selection.end - selection.start;
-        let start = Math.max(0, selection.start + diff);
-        let end = start + width;
-        if (end > CanvasLogicalWidth) {
-          end = CanvasLogicalWidth;
-          start = end - width;
-        }
-
-        setNewSelection({ start: start, end: end });
-        break;
-      }
-      case Mode.Selecting: {
-        if (x < moveOffsetX.current) {
-          setNewSelection({
-            start: x,
-            end: moveOffsetX.current,
-          });
-        } else {
-          setNewSelection({ start: moveOffsetX.current, end: x });
-        }
-        break;
-      }
-    }
-  };
-
-  const handleMouseUp = () => {
-    if (mode == Mode.Normal) {
-      return;
-    }
-
-    setMode(Mode.Normal);
-    setCursor('auto');
-
-    const start = Math.round(
-      (newSelection.start / CanvasLogicalWidth) * mediaSet.audioFrames
-    );
-    const end = Math.round(
-      (newSelection.end / CanvasLogicalWidth) * mediaSet.audioFrames
-    );
-    onSelectionChange({ start, end });
-  };
-
-  const handleMouseLeave = (_evt: MouseEvent<HTMLCanvasElement>) => {
-    setHoverState(HoverState.Normal);
-  };
+  // convert selection change from canvas pixels to frames, and trigger callback.
+  const handleSelectionChange = useCallback(
+    ({ start, end }: Selection) => {
+      onSelectionChange({
+        start: Math.round((start / CanvasLogicalWidth) * mediaSet.audioFrames),
+        end: Math.round((end / CanvasLogicalWidth) * mediaSet.audioFrames),
+      });
+    },
+    [mediaSet]
+  );
 
   // render component
 
@@ -324,15 +70,6 @@ export const Overview: React.FC<Props> = ({
     height: `${height}px`,
   } as React.CSSProperties;
 
-  const hudCanvasStyles = {
-    position: 'absolute',
-    width: '100%',
-    height: '100%',
-    display: 'block',
-    zIndex: 2,
-    cursor: cursor,
-  } as React.CSSProperties;
-
   return (
     <>
       <div style={containerStyles}>
@@ -346,15 +83,14 @@ export const Overview: React.FC<Props> = ({
           zIndex={1}
           alpha={1}
         ></WaveformCanvas>
-        <canvas
-          ref={hudCanvasRef}
+        <HudCanvas
           width={CanvasLogicalWidth}
           height={CanvasLogicalHeight}
-          style={hudCanvasStyles}
-          onMouseDown={handleMouseDown}
-          onMouseMove={handleMouseMove}
-          onMouseLeave={handleMouseLeave}
-        ></canvas>
+          zIndex={1}
+          position={position}
+          selection={selectedPixels}
+          onSelectionChange={handleSelectionChange}
+        />
       </div>
     </>
   );