Several fixes and adjustments

- Predict audio decoder config description only when the codec is AAC
- Validate Opus description before using it
- Validate `target` in the options

package.json

@@ -1,6 +1,6 @@
 {
   "name": "mp4-muxer",
-  "version": "5.1.2",
+  "version": "5.1.3",
   "description": "MP4 multiplexer in pure TypeScript with support for WebCodecs API, video & audio.",
   "main": "./build/mp4-muxer.js",
   "module": "./build/mp4-muxer.mjs",

src/box.ts

@@ -452,9 +452,15 @@ export const dOps = (track: AudioTrack) => {
 
 	// Read preskip and from codec private data from the encoder
 	// https://www.rfc-editor.org/rfc/rfc7845#section-5
-	const description = track.info.decoderConfig.description;
+	const description = track.info.decoderConfig?.description;
 	if (description) {
-		const view = new DataView(ArrayBuffer.isView(description) ? description.buffer : description);
+		if (description.byteLength < 18) {
+			throw new TypeError('Invalid decoder description provided for Opus; must be at least 18 bytes long.');
+		}
+
+		const view = ArrayBuffer.isView(description)
+			? new DataView(description.buffer, description.byteOffset, description.byteLength)
+			: new DataView(description);
 		preskip = view.getUint16(10, true);
 		gain = view.getInt16(14, true);
 	}

src/index.ts

@@ -1,2 +1,2 @@
 export { Muxer } from './muxer';
-export * from './target';
+export { ArrayBufferTarget, StreamTarget, FileSystemWritableFileStreamTarget } from './target';

src/muxer.ts

@@ -155,6 +155,10 @@ export class Muxer<T extends Target> {
 			throw new TypeError('The muxer requires an options object to be passed to its constructor.');
 		}
 
+		if (!(options.target instanceof Target)) {
+			throw new TypeError('The target must be provided and an instance of Target.');
+		}
+
 		if (options.video) {
 			if (!SUPPORTED_VIDEO_CODECS.includes(options.video.codec)) {
 				throw new TypeError(`Unsupported video codec: ${options.video.codec}`);
@@ -322,26 +326,14 @@ export class Muxer<T extends Target> {
 		}
 
 		if (this.#options.audio) {
-			// For the case that we don't get any further decoder details, we can still make a pretty educated guess:
-			let guessedCodecPrivate = this.#generateMpeg4AudioSpecificConfig(
-				2, // Object type for AAC-LC, since it's the most common
-				this.#options.audio.sampleRate,
-				this.#options.audio.numberOfChannels
-			);
-
 			this.#audioTrack = {
 				id: this.#options.video ? 2 : 1,
 				info: {
 					type: 'audio',
 					codec: this.#options.audio.codec,
 					numberOfChannels: this.#options.audio.numberOfChannels,
 					sampleRate: this.#options.audio.sampleRate,
-					decoderConfig: {
-						codec: this.#options.audio.codec,
-						description: guessedCodecPrivate,
-						numberOfChannels: this.#options.audio.numberOfChannels,
-						sampleRate: this.#options.audio.sampleRate
-					}
+					decoderConfig: null
 				},
 				timescale: this.#options.audio.sampleRate,
 				samples: [],
@@ -355,6 +347,22 @@ export class Muxer<T extends Target> {
 				lastSample: null,
 				compactlyCodedChunkTable: []
 			};
+
+			if (this.#options.audio.codec === 'aac') {
+				// For the case that we don't get any further decoder details, we can still make an educated guess:
+				let guessedCodecPrivate = this.#generateMpeg4AudioSpecificConfig(
+					2, // Object type for AAC-LC, since it's the most common
+					this.#options.audio.sampleRate,
+					this.#options.audio.numberOfChannels
+				);
+
+				this.#audioTrack.info.decoderConfig = {
+					codec: this.#options.audio.codec,
+					description: guessedCodecPrivate,
+					numberOfChannels: this.#options.audio.numberOfChannels,
+					sampleRate: this.#options.audio.sampleRate
+				};
+			}
 		}
 	}