Use subarray instead of slice for more performant Uint8Array copying

src/source/canvas_source.js

@@ -129,7 +129,7 @@ class CanvasSource extends ImageSource {
             const imageData = this.secondaryContext.createImageData(this.width, this.height);
             const flipped = new Uint8Array(this.width * this.height * 4);
             for (let i = this.height - 1, j = 0; i >= 0; i--, j++) {
-                flipped.set(data.slice(i * this.width * 4, (i + 1) * this.width * 4), j * this.width * 4);
+                flipped.set(data.subarray(i * this.width * 4, (i + 1) * this.width * 4), j * this.width * 4);
             }
             imageData.data.set(flipped);
             return imageData;