Allow clusters starting with delta chunks

Author: Vanilagy

README.md

@@ -292,14 +292,6 @@ await fileStream.close();
 ```
 
 ## Details
-### Video key frame frequency
-Canonical WebM files can only have a maximum Matroska Cluster length of 32.768 seconds, and each cluster must begin with
-a video key frame. You therefore need to tell your `VideoEncoder` to encode a `VideoFrame` as a key frame at least every
-32 seconds, otherwise your WebM file will be incorrect. You can do this by doing:
-```js
-videoEncoder.encode(frame, { keyFrame: true });
-```
-
 ### Media chunk buffering
 When muxing a file with a video **and** an audio track, it is important that the individual chunks inside the WebM file
 be stored in monotonically increasing time. This does mean, however, that the multiplexer must buffer chunks of one

build/webm-muxer.js

@@ -1,6 +1,6 @@
 {
   "name": "webm-muxer",
-  "version": "5.0.4",
+  "version": "5.1.0",
   "description": "WebM multiplexer in pure TypeScript with support for WebCodecs API, video & audio.",
   "main": "./build/webm-muxer.js",
   "module": "./build/webm-muxer.mjs",

build/webm-muxer.min.js

@@ -755,33 +755,29 @@ export class Muxer<T extends Target> {
 		}
 
 		let msTimestamp = Math.floor(chunk.timestamp / 1000);
+		let relativeTimestamp = msTimestamp - this.#currentClusterTimestamp;
+
 		let shouldCreateNewClusterFromKeyFrame =
 			canCreateNewCluster &&
 			chunk.type === 'key' &&
-			msTimestamp - this.#currentClusterTimestamp >= 1000;
+			relativeTimestamp >= 1000;
+		let clusterWouldBeTooLong = relativeTimestamp >= MAX_CHUNK_LENGTH_MS;
 
 		if (
 			!this.#currentCluster ||
-			shouldCreateNewClusterFromKeyFrame
+			shouldCreateNewClusterFromKeyFrame ||
+			// If we hit this case, then we're sadly forced to create a chunk that starts with a delta chunk
+			clusterWouldBeTooLong
 		) {
 			this.#createNewCluster(msTimestamp);
+			relativeTimestamp = 0;
 		}
 
-		let relativeTimestamp = msTimestamp - this.#currentClusterTimestamp;
 		if (relativeTimestamp < 0) {
-			// The chunk lies out of the current cluster
+			// The chunk lies outside of the current cluster
 			return;
 		}
 
-		let clusterIsTooLong = relativeTimestamp >= MAX_CHUNK_LENGTH_MS;
-		if (clusterIsTooLong) {
-			throw new Error(
-				`Current Matroska cluster exceeded its maximum allowed length of ${MAX_CHUNK_LENGTH_MS} ` +
-				`milliseconds. In order to produce a correct WebM file, you must pass in a key frame at least every ` +
-				`${MAX_CHUNK_LENGTH_MS} milliseconds.`
-			);
-		}
-
 		let prelude = new Uint8Array(4);
 		let view = new DataView(prelude.buffer);
 		// 0x80 to indicate it's the last byte of a multi-byte number