Allow all Matroska AttachedFiles to be read & written via metadata tags

dev/demux.html

@@ -14,6 +14,9 @@
 			source: new Mediabunny.BlobSource(file),
 		});
 
+		console.log(await input.getMetadataTags());
+
+		/*
 		console.log(await input.computeDuration());
 		return;
 
@@ -25,6 +28,7 @@
 		}
 
 		console.log("Done")
+		*/
 
 
 		/*