Improve error messages in examples

examples/thumbnail-generation/thumbnail-generation.ts

@@ -15,7 +15,7 @@ const THUMBNAIL_SIZE = 200;
 const generateThumbnails = async (file: File) => {
 	fileNameElement.textContent = file.name;
 	horizontalRule.style.display = '';
-	errorElement.innerHTML = '';
+	errorElement.textContent = '';
 	thumbnailContainer.innerHTML = '';
 
 	try {
@@ -30,6 +30,14 @@ const generateThumbnails = async (file: File) => {
 			throw new Error('File has no video track.');
 		}
 
+		if (videoTrack.codec === null) {
+			throw new Error('Unsupported video codec.');
+		}
+
+		if (!(await videoTrack.canDecode())) {
+			throw new Error('Unable to decode the video track.');
+		}
+
 		// Compute width and height of the thumbnails such that the larger dimension is equal to THUMBNAIL_SIZE
 		const width = videoTrack.displayWidth > videoTrack.displayHeight
 			? THUMBNAIL_SIZE