Update thumbnail generation example to use cursors

examples/thumbnail-generation/thumbnail-generation.ts

@@ -1,6 +1,7 @@
-import { Input, ALL_FORMATS, BlobSource, UrlSource, CanvasSink } from 'mediabunny';
+import { Input, ALL_FORMATS, BlobSource, UrlSource, VideoSampleCursor } from 'mediabunny';
 
 import SampleFileUrl from '../../docs/assets/big-buck-bunny-trimmed.mp4';
+import { canvasTransformer } from '../../src/cursors.js';
 (document.querySelector('#sample-file-download') as HTMLAnchorElement).href = SampleFileUrl;
 
 const selectMediaButton = document.querySelector('#select-file') as HTMLButtonElement;
@@ -69,16 +70,23 @@ const generateThumbnails = async (resource: File | string) => {
 			(_, i) => firstTimestamp + i * (lastTimestamp - firstTimestamp) / THUMBNAIL_COUNT,
 		);
 
-		// Create a CanvasSink for extracting resized frames from the video track
-		const sink = new CanvasSink(videoTrack, {
-			width: Math.floor(width * window.devicePixelRatio),
-			height: Math.floor(height * window.devicePixelRatio),
-			fit: 'fill',
+		// Create a cursor to extract frames from the video
+		const cursor = new VideoSampleCursor(videoTrack, {
+			transform: canvasTransformer({
+				width: Math.floor(width * window.devicePixelRatio),
+				height: Math.floor(height * window.devicePixelRatio),
+				fit: 'fill',
+			}),
 		});
 
+		// Queue all cursor commands at once, including closing the cursor; this allows it to optimize access patterns
+		const promises = timestamps.map(x => cursor.seekTo(x));
+		void cursor.close();
+
 		// Iterate over all thumbnail canvases
 		let i = 0;
-		for await (const wrappedCanvas of sink.canvasesAtTimestamps(timestamps)) {
+		for (const promise of promises) {
+			const wrappedCanvas = await promise;
 			const container = thumbnailElements[i]!;
 
 			if (wrappedCanvas) {

src/cursors.ts

@@ -930,7 +930,6 @@ export abstract class SampleCursor<
 		this._lastPendingRequest = pendingRequest;
 
 		this._pumpGate.open();
-
 		deferred.execute(); // Waiting for the return would be too long
 
 		return res.set(await request.promise);
@@ -987,6 +986,7 @@ export abstract class SampleCursor<
 		}
 		this._lastPendingRequest = pendingRequest;
 
+		this._pumpGate.open();
 		lock.release(); // Waiting for the return would be too long
 
 		return res.set(await request.promise);

src/isobmff/isobmff-demuxer.ts

@@ -2368,7 +2368,10 @@ abstract class IsobmffTrackBacking implements InputTrackBacking {
 	}
 
 	async getFirstTimestamp() {
-		const firstPacket = await this.getFirstPacket({ metadataOnly: true });
+		const result = new ResultValue<EncodedPacket | null>();
+		await this.getFirstPacket(result, { metadataOnly: true });
+
+		const firstPacket = result.value;
 		return firstPacket?.timestamp ?? 0;
 	}