feat: implement multi-track waveform selection and editing with undo/redo

Added comprehensive selection and editing capabilities to multi-track editor:
- Visual selection overlay with Shift+drag interaction on waveforms
- Multi-track edit commands (cut, copy, paste, delete, duplicate)
- Full keyboard shortcut support (Ctrl+X/C/V/D, Delete, Ctrl+Z/Y)
- Complete undo/redo integration via command pattern
- Per-track selection state with localStorage persistence
- Audio buffer manipulation utilities (extract, insert, delete, duplicate segments)
- Toast notifications for all edit operations
- Red playhead to distinguish from blue selection overlay

All edit operations are fully undoable and integrated with the existing
history manager system.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

components/editor/AudioEditor.tsx

@@ -14,15 +14,30 @@ import { useToast } from '@/components/ui/Toast';
 import { TrackList } from '@/components/tracks/TrackList';
 import { ImportTrackDialog } from '@/components/tracks/ImportTrackDialog';
 import { formatDuration } from '@/lib/audio/decoder';
+import { useHistory } from '@/lib/hooks/useHistory';
+import {
+  createMultiTrackCutCommand,
+  createMultiTrackCopyCommand,
+  createMultiTrackDeleteCommand,
+  createMultiTrackPasteCommand,
+  createMultiTrackDuplicateCommand,
+} from '@/lib/history/commands/multi-track-edit-command';
+import { extractBufferSegment } from '@/lib/audio/buffer-utils';
 
 export function AudioEditor() {
   const [importDialogOpen, setImportDialogOpen] = React.useState(false);
   const [selectedTrackId, setSelectedTrackId] = React.useState<string | null>(null);
   const [zoom, setZoom] = React.useState(1);
   const [masterVolume, setMasterVolume] = React.useState(0.8);
+  const [clipboard, setClipboard] = React.useState<AudioBuffer | null>(null);
 
   const { addToast } = useToast();
 
+  // Command history for undo/redo
+  const { execute: executeCommand, undo, redo, state: historyState } = useHistory();
+  const canUndo = historyState.canUndo;
+  const canRedo = historyState.canRedo;
+
   // Multi-track hooks
   const {
     tracks,
@@ -135,6 +150,146 @@ export function AudioEditor() {
     updateTrack(selectedTrack.id, { effectChain: updatedChain });
   };
 
+  // Selection handler
+  const handleSelectionChange = (trackId: string, selection: { start: number; end: number } | null) => {
+    updateTrack(trackId, { selection });
+  };
+
+  // Edit handlers
+  const handleCut = React.useCallback(() => {
+    const track = tracks.find((t) => t.selection);
+    if (!track || !track.audioBuffer || !track.selection) return;
+
+    // Extract to clipboard
+    const extracted = extractBufferSegment(
+      track.audioBuffer,
+      track.selection.start,
+      track.selection.end
+    );
+    setClipboard(extracted);
+
+    // Execute cut command
+    const command = createMultiTrackCutCommand(
+      track.id,
+      track.audioBuffer,
+      track.selection,
+      (trackId, buffer, selection) => {
+        updateTrack(trackId, { audioBuffer: buffer, selection });
+      }
+    );
+    executeCommand(command);
+
+    addToast({
+      title: 'Cut',
+      description: 'Selection cut to clipboard',
+      variant: 'success',
+      duration: 2000,
+    });
+  }, [tracks, executeCommand, updateTrack, addToast]);
+
+  const handleCopy = React.useCallback(() => {
+    const track = tracks.find((t) => t.selection);
+    if (!track || !track.audioBuffer || !track.selection) return;
+
+    // Extract to clipboard
+    const extracted = extractBufferSegment(
+      track.audioBuffer,
+      track.selection.start,
+      track.selection.end
+    );
+    setClipboard(extracted);
+
+    // Execute copy command (doesn't modify buffer, just for undo history)
+    const command = createMultiTrackCopyCommand(
+      track.id,
+      track.audioBuffer,
+      track.selection,
+      (trackId, buffer, selection) => {
+        updateTrack(trackId, { audioBuffer: buffer, selection });
+      }
+    );
+    executeCommand(command);
+
+    addToast({
+      title: 'Copy',
+      description: 'Selection copied to clipboard',
+      variant: 'success',
+      duration: 2000,
+    });
+  }, [tracks, executeCommand, updateTrack, addToast]);
+
+  const handlePaste = React.useCallback(() => {
+    if (!clipboard || !selectedTrackId) return;
+
+    const track = tracks.find((t) => t.id === selectedTrackId);
+    if (!track) return;
+
+    // Paste at current time or at end of buffer
+    const pastePosition = currentTime || track.audioBuffer?.duration || 0;
+
+    const command = createMultiTrackPasteCommand(
+      track.id,
+      track.audioBuffer,
+      clipboard,
+      pastePosition,
+      (trackId, buffer, selection) => {
+        updateTrack(trackId, { audioBuffer: buffer, selection });
+      }
+    );
+    executeCommand(command);
+
+    addToast({
+      title: 'Paste',
+      description: 'Clipboard content pasted',
+      variant: 'success',
+      duration: 2000,
+    });
+  }, [clipboard, selectedTrackId, tracks, currentTime, executeCommand, updateTrack, addToast]);
+
+  const handleDelete = React.useCallback(() => {
+    const track = tracks.find((t) => t.selection);
+    if (!track || !track.audioBuffer || !track.selection) return;
+
+    const command = createMultiTrackDeleteCommand(
+      track.id,
+      track.audioBuffer,
+      track.selection,
+      (trackId, buffer, selection) => {
+        updateTrack(trackId, { audioBuffer: buffer, selection });
+      }
+    );
+    executeCommand(command);
+
+    addToast({
+      title: 'Delete',
+      description: 'Selection deleted',
+      variant: 'success',
+      duration: 2000,
+    });
+  }, [tracks, executeCommand, updateTrack, addToast]);
+
+  const handleDuplicate = React.useCallback(() => {
+    const track = tracks.find((t) => t.selection);
+    if (!track || !track.audioBuffer || !track.selection) return;
+
+    const command = createMultiTrackDuplicateCommand(
+      track.id,
+      track.audioBuffer,
+      track.selection,
+      (trackId, buffer, selection) => {
+        updateTrack(trackId, { audioBuffer: buffer, selection });
+      }
+    );
+    executeCommand(command);
+
+    addToast({
+      title: 'Duplicate',
+      description: 'Selection duplicated',
+      variant: 'success',
+      duration: 2000,
+    });
+  }, [tracks, executeCommand, updateTrack, addToast]);
+
   // Zoom controls
   const handleZoomIn = () => {
     setZoom((prev) => Math.min(20, prev + 1));
@@ -265,6 +420,59 @@ export function AudioEditor() {
 
       if (isTyping) return;
 
+      // Ctrl/Cmd+Z: Undo
+      if ((e.ctrlKey || e.metaKey) && e.key === 'z' && !e.shiftKey) {
+        e.preventDefault();
+        if (canUndo) {
+          undo();
+        }
+        return;
+      }
+
+      // Ctrl/Cmd+Shift+Z or Ctrl/Cmd+Y: Redo
+      if (((e.ctrlKey || e.metaKey) && e.key === 'z' && e.shiftKey) || ((e.ctrlKey || e.metaKey) && e.key === 'y')) {
+        e.preventDefault();
+        if (canRedo) {
+          redo();
+        }
+        return;
+      }
+
+      // Ctrl/Cmd+X: Cut
+      if ((e.ctrlKey || e.metaKey) && e.key === 'x') {
+        e.preventDefault();
+        handleCut();
+        return;
+      }
+
+      // Ctrl/Cmd+C: Copy
+      if ((e.ctrlKey || e.metaKey) && e.key === 'c') {
+        e.preventDefault();
+        handleCopy();
+        return;
+      }
+
+      // Ctrl/Cmd+V: Paste
+      if ((e.ctrlKey || e.metaKey) && e.key === 'v') {
+        e.preventDefault();
+        handlePaste();
+        return;
+      }
+
+      // Ctrl/Cmd+D: Duplicate
+      if ((e.ctrlKey || e.metaKey) && e.key === 'd') {
+        e.preventDefault();
+        handleDuplicate();
+        return;
+      }
+
+      // Delete or Backspace: Delete selection
+      if (e.key === 'Delete' || e.key === 'Backspace') {
+        e.preventDefault();
+        handleDelete();
+        return;
+      }
+
       // Escape: Clear selection
       if (e.key === 'Escape') {
         e.preventDefault();
@@ -274,7 +482,7 @@ export function AudioEditor() {
 
     window.addEventListener('keydown', handleKeyDown);
     return () => window.removeEventListener('keydown', handleKeyDown);
-  }, [togglePlayPause]);
+  }, [togglePlayPause, canUndo, canRedo, undo, redo, handleCut, handleCopy, handlePaste, handleDelete, handleDuplicate]);
 
   return (
     <>
@@ -331,6 +539,7 @@ export function AudioEditor() {
               onRemoveTrack={handleRemoveTrack}
               onUpdateTrack={updateTrack}
               onSeek={seek}
+              onSelectionChange={handleSelectionChange}
             />
           </div>
 

components/tracks/Track.tsx

@@ -30,6 +30,7 @@ export interface TrackProps {
   onRemoveEffect?: (effectId: string) => void;
   onUpdateEffect?: (effectId: string, parameters: any) => void;
   onAddEffect?: (effectType: EffectType) => void;
+  onSelectionChange?: (selection: { start: number; end: number } | null) => void;
 }
 
 export function Track({
@@ -52,6 +53,7 @@ export function Track({
   onRemoveEffect,
   onUpdateEffect,
   onAddEffect,
+  onSelectionChange,
 }: TrackProps) {
   const canvasRef = React.useRef<HTMLCanvasElement>(null);
   const containerRef = React.useRef<HTMLDivElement>(null);
@@ -63,6 +65,10 @@ export function Track({
   const [themeKey, setThemeKey] = React.useState(0);
   const inputRef = React.useRef<HTMLInputElement>(null);
 
+  // Selection state
+  const [isSelecting, setIsSelecting] = React.useState(false);
+  const [selectionStart, setSelectionStart] = React.useState<number | null>(null);
+
   const handleNameClick = () => {
     setIsEditingName(true);
     setNameInput(String(track.name || 'Untitled Track'));
@@ -175,27 +181,98 @@ export function Track({
     ctx.lineTo(width, height / 2);
     ctx.stroke();
 
+    // Draw selection overlay
+    if (track.selection && duration > 0) {
+      const selStartX = (track.selection.start / duration) * width;
+      const selEndX = (track.selection.end / duration) * width;
+
+      // Draw selection background
+      ctx.fillStyle = 'rgba(59, 130, 246, 0.2)';
+      ctx.fillRect(selStartX, 0, selEndX - selStartX, height);
+
+      // Draw selection borders
+      ctx.strokeStyle = 'rgba(59, 130, 246, 0.8)';
+      ctx.lineWidth = 2;
+
+      // Start border
+      ctx.beginPath();
+      ctx.moveTo(selStartX, 0);
+      ctx.lineTo(selStartX, height);
+      ctx.stroke();
+
+      // End border
+      ctx.beginPath();
+      ctx.moveTo(selEndX, 0);
+      ctx.lineTo(selEndX, height);
+      ctx.stroke();
+    }
+
     // Draw playhead
     if (duration > 0) {
       const playheadX = (currentTime / duration) * width;
-      ctx.strokeStyle = 'rgba(59, 130, 246, 0.8)';
+      ctx.strokeStyle = 'rgba(239, 68, 68, 0.8)';
       ctx.lineWidth = 2;
       ctx.beginPath();
       ctx.moveTo(playheadX, 0);
       ctx.lineTo(playheadX, height);
       ctx.stroke();
     }
-  }, [track.audioBuffer, track.color, track.collapsed, track.height, zoom, currentTime, duration, themeKey]);
+  }, [track.audioBuffer, track.color, track.collapsed, track.height, zoom, currentTime, duration, themeKey, track.selection]);
 
-  const handleCanvasClick = (e: React.MouseEvent<HTMLCanvasElement>) => {
-    if (!onSeek || !duration) return;
+  const handleCanvasMouseDown = (e: React.MouseEvent<HTMLCanvasElement>) => {
+    if (!duration) return;
 
     const rect = e.currentTarget.getBoundingClientRect();
     const x = e.clientX - rect.left;
     const clickTime = (x / rect.width) * duration;
+
+    // Shift+drag to create selection
+    if (e.shiftKey) {
+      setIsSelecting(true);
+      setSelectionStart(clickTime);
+      onSelectionChange?.({ start: clickTime, end: clickTime });
+    } else {
+      // Regular click clears selection and seeks
+      onSelectionChange?.(null);
+      if (onSeek) {
         onSeek(clickTime);
+      }
+    }
   };
 
+  const handleCanvasMouseMove = (e: React.MouseEvent<HTMLCanvasElement>) => {
+    if (!isSelecting || selectionStart === null || !duration) return;
+
+    const rect = e.currentTarget.getBoundingClientRect();
+    const x = e.clientX - rect.left;
+    const currentTime = (x / rect.width) * duration;
+
+    // Clamp to valid time range
+    const clampedTime = Math.max(0, Math.min(duration, currentTime));
+
+    // Update selection (ensure start < end)
+    const start = Math.min(selectionStart, clampedTime);
+    const end = Math.max(selectionStart, clampedTime);
+
+    onSelectionChange?.({ start, end });
+  };
+
+  const handleCanvasMouseUp = () => {
+    setIsSelecting(false);
+  };
+
+  // Handle mouse leaving canvas during selection
+  React.useEffect(() => {
+    const handleGlobalMouseUp = () => {
+      if (isSelecting) {
+        setIsSelecting(false);
+      }
+    };
+
+    window.addEventListener('mouseup', handleGlobalMouseUp);
+    return () => window.removeEventListener('mouseup', handleGlobalMouseUp);
+  }, [isSelecting]);
+
   const handleFileChange = async (e: React.ChangeEvent<HTMLInputElement>) => {
     const file = e.target.files?.[0];
     if (!file || !onLoadAudio) return;
@@ -422,8 +499,10 @@ export function Track({
         {track.audioBuffer ? (
           <canvas
             ref={canvasRef}
-            className="absolute inset-0 w-full h-full cursor-pointer"
-            onClick={handleCanvasClick}
+            className="absolute inset-0 w-full h-full cursor-crosshair"
+            onMouseDown={handleCanvasMouseDown}
+            onMouseMove={handleCanvasMouseMove}
+            onMouseUp={handleCanvasMouseUp}
           />
         ) : (
           !track.collapsed && (

components/tracks/TrackList.tsx

@@ -20,6 +20,7 @@ export interface TrackListProps {
   onRemoveTrack: (trackId: string) => void;
   onUpdateTrack: (trackId: string, updates: Partial<TrackType>) => void;
   onSeek?: (time: number) => void;
+  onSelectionChange?: (trackId: string, selection: { start: number; end: number } | null) => void;
 }
 
 export function TrackList({
@@ -34,6 +35,7 @@ export function TrackList({
   onRemoveTrack,
   onUpdateTrack,
   onSeek,
+  onSelectionChange,
 }: TrackListProps) {
   const [importDialogOpen, setImportDialogOpen] = React.useState(false);
 
@@ -144,6 +146,11 @@ export function TrackList({
               };
               onUpdateTrack(track.id, { effectChain: updatedChain });
             }}
+            onSelectionChange={
+              onSelectionChange
+                ? (selection) => onSelectionChange(track.id, selection)
+                : undefined
+            }
           />
         ))}
       </div>

lib/audio/buffer-utils.ts

@@ -165,3 +165,15 @@ export function concatenateBuffers(
 
   return newBuffer;
 }
+
+/**
+ * Duplicate a segment of audio buffer (extract and insert it after the selection)
+ */
+export function duplicateBufferSegment(
+  buffer: AudioBuffer,
+  startTime: number,
+  endTime: number
+): AudioBuffer {
+  const segment = extractBufferSegment(buffer, startTime, endTime);
+  return insertBufferSegment(buffer, segment, endTime);
+}

lib/audio/track-utils.ts

@@ -37,6 +37,7 @@ export function createTrack(name?: string, color?: TrackColor): Track {
     effectChain: createEffectChain(`${trackName} Effects`),
     collapsed: false,
     selected: false,
+    selection: null,
   };
 }
 

lib/history/commands/multi-track-edit-command.ts

@@ -0,0 +1,190 @@
+/**
+ * Multi-track edit commands for audio operations across tracks
+ */
+
+import { BaseCommand } from '../command';
+import type { Track } from '@/types/track';
+import type { Selection } from '@/types/selection';
+import {
+  extractBufferSegment,
+  deleteBufferSegment,
+  insertBufferSegment,
+  duplicateBufferSegment,
+} from '@/lib/audio/buffer-utils';
+
+export type MultiTrackEditType = 'cut' | 'copy' | 'delete' | 'paste' | 'duplicate';
+
+export interface MultiTrackEditParams {
+  type: MultiTrackEditType;
+  trackId: string;
+  beforeBuffer: AudioBuffer | null;
+  afterBuffer: AudioBuffer | null;
+  selection?: Selection;
+  clipboardData?: AudioBuffer;
+  pastePosition?: number;
+  onApply: (trackId: string, buffer: AudioBuffer | null, selection: Selection | null) => void;
+}
+
+/**
+ * Command for multi-track edit operations
+ */
+export class MultiTrackEditCommand extends BaseCommand {
+  private type: MultiTrackEditType;
+  private trackId: string;
+  private beforeBuffer: AudioBuffer | null;
+  private afterBuffer: AudioBuffer | null;
+  private selection?: Selection;
+  private clipboardData?: AudioBuffer;
+  private pastePosition?: number;
+  private onApply: (trackId: string, buffer: AudioBuffer | null, selection: Selection | null) => void;
+
+  constructor(params: MultiTrackEditParams) {
+    super();
+    this.type = params.type;
+    this.trackId = params.trackId;
+    this.beforeBuffer = params.beforeBuffer;
+    this.afterBuffer = params.afterBuffer;
+    this.selection = params.selection;
+    this.clipboardData = params.clipboardData;
+    this.pastePosition = params.pastePosition;
+    this.onApply = params.onApply;
+  }
+
+  execute(): void {
+    // For copy, don't modify the buffer, just update selection
+    if (this.type === 'copy') {
+      this.onApply(this.trackId, this.beforeBuffer, this.selection || null);
+    } else {
+      this.onApply(this.trackId, this.afterBuffer, null);
+    }
+  }
+
+  undo(): void {
+    this.onApply(this.trackId, this.beforeBuffer, null);
+  }
+
+  getDescription(): string {
+    switch (this.type) {
+      case 'cut':
+        return 'Cut';
+      case 'copy':
+        return 'Copy';
+      case 'delete':
+        return 'Delete';
+      case 'paste':
+        return 'Paste';
+      case 'duplicate':
+        return 'Duplicate';
+      default:
+        return 'Edit';
+    }
+  }
+}
+
+/**
+ * Factory functions to create multi-track edit commands
+ */
+
+export function createMultiTrackCutCommand(
+  trackId: string,
+  buffer: AudioBuffer,
+  selection: Selection,
+  onApply: (trackId: string, buffer: AudioBuffer | null, selection: Selection | null) => void
+): MultiTrackEditCommand {
+  const afterBuffer = deleteBufferSegment(buffer, selection.start, selection.end);
+
+  return new MultiTrackEditCommand({
+    type: 'cut',
+    trackId,
+    beforeBuffer: buffer,
+    afterBuffer,
+    selection,
+    onApply,
+  });
+}
+
+export function createMultiTrackCopyCommand(
+  trackId: string,
+  buffer: AudioBuffer,
+  selection: Selection,
+  onApply: (trackId: string, buffer: AudioBuffer | null, selection: Selection | null) => void
+): MultiTrackEditCommand {
+  // Copy doesn't modify the buffer
+  return new MultiTrackEditCommand({
+    type: 'copy',
+    trackId,
+    beforeBuffer: buffer,
+    afterBuffer: buffer,
+    selection,
+    onApply,
+  });
+}
+
+export function createMultiTrackDeleteCommand(
+  trackId: string,
+  buffer: AudioBuffer,
+  selection: Selection,
+  onApply: (trackId: string, buffer: AudioBuffer | null, selection: Selection | null) => void
+): MultiTrackEditCommand {
+  const afterBuffer = deleteBufferSegment(buffer, selection.start, selection.end);
+
+  return new MultiTrackEditCommand({
+    type: 'delete',
+    trackId,
+    beforeBuffer: buffer,
+    afterBuffer,
+    selection,
+    onApply,
+  });
+}
+
+export function createMultiTrackPasteCommand(
+  trackId: string,
+  buffer: AudioBuffer | null,
+  clipboardData: AudioBuffer,
+  pastePosition: number,
+  onApply: (trackId: string, buffer: AudioBuffer | null, selection: Selection | null) => void
+): MultiTrackEditCommand {
+  const targetBuffer = buffer || createSilentBuffer(clipboardData.sampleRate, clipboardData.numberOfChannels, pastePosition);
+  const afterBuffer = insertBufferSegment(targetBuffer, clipboardData, pastePosition);
+
+  return new MultiTrackEditCommand({
+    type: 'paste',
+    trackId,
+    beforeBuffer: buffer,
+    afterBuffer,
+    clipboardData,
+    pastePosition,
+    onApply,
+  });
+}
+
+export function createMultiTrackDuplicateCommand(
+  trackId: string,
+  buffer: AudioBuffer,
+  selection: Selection,
+  onApply: (trackId: string, buffer: AudioBuffer | null, selection: Selection | null) => void
+): MultiTrackEditCommand {
+  const afterBuffer = duplicateBufferSegment(buffer, selection.start, selection.end);
+
+  return new MultiTrackEditCommand({
+    type: 'duplicate',
+    trackId,
+    beforeBuffer: buffer,
+    afterBuffer,
+    selection,
+    onApply,
+  });
+}
+
+/**
+ * Helper function to create a silent buffer
+ */
+function createSilentBuffer(sampleRate: number, numberOfChannels: number, duration: number): AudioBuffer {
+  const audioContext = new OfflineAudioContext(
+    numberOfChannels,
+    Math.ceil(duration * sampleRate),
+    sampleRate
+  );
+  return audioContext.createBuffer(numberOfChannels, Math.ceil(duration * sampleRate), sampleRate);
+}

lib/hooks/useMultiTrack.ts

@@ -31,6 +31,7 @@ export function useMultiTrack() {
           name: String(t.name || 'Untitled Track'), // Ensure name is always a string
           audioBuffer: null, // Will need to be reloaded
           effectChain: t.effectChain || createEffectChain(`${t.name} Effects`), // Restore effect chain or create new
+          selection: t.selection || null, // Initialize selection
         }));
       }
     } catch (error) {

types/track.ts

@@ -3,6 +3,7 @@
  */
 
 import type { EffectChain } from '@/lib/audio/effects/chain';
+import type { Selection } from './selection';
 
 export interface Track {
   id: string;
@@ -24,6 +25,9 @@ export interface Track {
   // UI state
   collapsed: boolean;
   selected: boolean;
+
+  // Selection (for editing operations)
+  selection: Selection | null;
 }
 
 export interface TrackState {