Add video speed control and improve playback smoothness

Added a speed control dropdown in the timeline toolbar that lets users change video playback speed between 0.5x to 2x. The dropdown shows the current speed and offers preset options.

Made video playback smoother by:
- Using better timing for speed changes
- Improving video synchronization
- Reducing playback stutters
- Making speed changes more responsive

The speed control is now easily accessible while editing and works smoothly with all video clips.

apps/web/src/components/editor/timeline.tsx

@@ -28,6 +28,13 @@ import { usePlaybackStore } from "@/stores/playback-store";
 import { processMediaFiles } from "@/lib/media-processing";
 import { toast } from "sonner";
 import { useState, useRef, useEffect } from "react";
+import {
+  Select,
+  SelectContent,
+  SelectItem,
+  SelectTrigger,
+  SelectValue,
+} from "../ui/select";
 
 export function Timeline() {
   // Timeline shows all tracks (video, audio, effects) and their clips.
@@ -36,7 +43,7 @@ export function Timeline() {
   const { tracks, addTrack, addClipToTrack, removeTrack, toggleTrackMute, removeClipFromTrack, moveClipToTrack, getTotalDuration } =
     useTimelineStore();
   const { mediaItems, addMediaItem } = useMediaStore();
-  const { currentTime, duration, seek, setDuration, isPlaying, play, pause, toggle } = usePlaybackStore();
+  const { currentTime, duration, seek, setDuration, isPlaying, play, pause, toggle, setSpeed, speed } = usePlaybackStore();
   const [isDragOver, setIsDragOver] = useState(false);
   const [isProcessing, setIsProcessing] = useState(false);
   const [zoomLevel, setZoomLevel] = useState(1);
@@ -331,6 +338,29 @@ export function Timeline() {
             </TooltipTrigger>
             <TooltipContent>Delete clip (Delete)</TooltipContent>
           </Tooltip>
+
+          <div className="w-px h-6 bg-border mx-1" />
+
+          {/* Speed Control */}
+          <Tooltip>
+            <TooltipTrigger asChild>
+              <Select
+                value={speed.toFixed(1)}
+                onValueChange={(value) => setSpeed(parseFloat(value))}
+              >
+                <SelectTrigger className="w-[90px] h-8">
+                  <SelectValue placeholder="1.0x" />
+                </SelectTrigger>
+                <SelectContent>
+                  <SelectItem value="0.5">0.5x</SelectItem>
+                  <SelectItem value="1.0">1.0x</SelectItem>
+                  <SelectItem value="1.5">1.5x</SelectItem>
+                  <SelectItem value="2.0">2.0x</SelectItem>
+                </SelectContent>
+              </Select>
+            </TooltipTrigger>
+            <TooltipContent>Playback Speed</TooltipContent>
+          </Tooltip>
         </TooltipProvider>
       </div>