diff --git a/dev/convert.html b/dev/convert.html
index cdcccb2..ec051d3 100644
--- a/dev/convert.html
+++ b/dev/convert.html
@@ -223,7 +223,7 @@
 				start,
 				end: start + 5,
 				//start: 0,
-				//end: 10
+				end: 10
 			},
 		});
 		console.log(conversion);
diff --git a/dev/live.html b/dev/live.html
index bdd2fc2..d21faec 100644
--- a/dev/live.html
+++ b/dev/live.html
@@ -19,7 +19,7 @@
     button.addEventListener('click', async () => {
         const stream = await navigator.mediaDevices.getDisplayMedia({ video: true, audio: false });
         const videoTrack = stream.getVideoTracks()[0];
-        const audioTrack = null;//stream.getAudioTracks()[0];
+        const audioTrack = stream.getAudioTracks()[0];
 
         const output = new Mediabunny.Output({
             target: new Mediabunny.BufferTarget(),
@@ -29,7 +29,7 @@
 		let audioSource = null;
         if (videoTrack) {
             videoSource = new Mediabunny.MediaStreamVideoTrackSource(videoTrack, {
-                codec: 'avc',
+                codec: 'vp9',
                 bitrate: Mediabunny.QUALITY_MEDIUM,
 				sizeChangeBehavior: 'passThrough',
             });
@@ -40,13 +40,13 @@
         }
         if (audioTrack) {
             audioSource = new Mediabunny.MediaStreamAudioTrackSource(audioTrack, {
-                codec: 'mp3',
+                codec: 'opus',
                 bitrate: Mediabunny.QUALITY_MEDIUM
             });
 
             audioSource.errorPromise.catch((d) => console.log("Hello!!???", d));
 
-            //output.addAudioTrack(audioSource);
+            output.addAudioTrack(audioSource);
         }
 
         await output.start();
diff --git a/docs/.vitepress/config.mts b/docs/.vitepress/config.mts
index 68e6167..5bc8da9 100644
--- a/docs/.vitepress/config.mts
+++ b/docs/.vitepress/config.mts
@@ -17,6 +17,7 @@ export default withMermaid({
 	sitemap: {
 		hostname: 'https://mediabunny.dev',
 	},
+	lastUpdated: true,
 	head: [
 		['link', { rel: 'icon', type: 'image/png', href: '/mediabunny-logo.png' }],
 		['link', { rel: 'icon', type: 'image/svg+xml', href: '/mediabunny-logo.svg' }],
diff --git a/docs/guide/media-sinks.md b/docs/guide/media-sinks.md
index 84747cb..077630a 100644
--- a/docs/guide/media-sinks.md
+++ b/docs/guide/media-sinks.md
@@ -97,9 +97,13 @@ await sink.getKeyPacket(5); // => EncodedPacket | null
 
 When retrieving a packet using a timestamp, the last packet (in [presentation order](#decode-vs-presentation-order)) with a timestamp less than or equal to the search timestamp will be returned. The methods return `null` if there exists no such packet.
 
-There is a special method for retrieving the first packet (in [decode order](#decode-vs-presentation-order)):
+There are special methods for retrieving the first packet (in [decode order](#decode-vs-presentation-order)):
 ```ts
 await sink.getFirstPacket(); // => EncodedPacket | null
+
+// The first packet is typically a key frame, but this is not required.
+// This method returns the first key frame:
+await sink.getFirstKeyPacket(); // => EncodedPacket | null
 ```
 The last packet (in [presentation order](#decode-vs-presentation-order)) can be retrieved like so:
 ```ts
diff --git a/docs/public/robots.txt b/docs/public/robots.txt
new file mode 100644
index 0000000..32ad9f2
--- /dev/null
+++ b/docs/public/robots.txt
@@ -0,0 +1,4 @@
+User-agent: *
+Allow: /
+
+Sitemap: https://mediabunny.dev/sitemap.xml
\ No newline at end of file
diff --git a/package-lock.json b/package-lock.json
index 3c36243..f003e96 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "mediabunny",
-  "version": "1.38.0",
+  "version": "1.39.2",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "mediabunny",
-      "version": "1.38.0",
+      "version": "1.39.2",
       "license": "MPL-2.0",
       "workspaces": [
         "packages/*"
@@ -7751,9 +7751,9 @@
       }
     },
     "node_modules/mediabunny": {
-      "version": "1.37.0",
-      "resolved": "https://registry.npmjs.org/mediabunny/-/mediabunny-1.37.0.tgz",
-      "integrity": "sha512-eV7M9IJ29pr/8RNL1sYtIxNbdMfDMN1hMwMaOFfNLhwuKKGSC+eKwiJFpdVjEJ3zrMA4LGerF4Hps0SENFSAlg==",
+      "version": "1.39.1",
+      "resolved": "https://registry.npmjs.org/mediabunny/-/mediabunny-1.39.1.tgz",
+      "integrity": "sha512-gaQKDWtfLhgSN9tRj37lgznHf9MOvey7sbT6GdQA7mWl1kaE5R+P1lfl9CDsgtzongx12IG9X/y2vgZmTHzGDg==",
       "license": "MPL-2.0",
       "peer": true,
       "workspaces": [
@@ -12077,7 +12077,7 @@
     },
     "packages/aac-encoder": {
       "name": "@mediabunny/aac-encoder",
-      "version": "1.38.0",
+      "version": "1.39.2",
       "license": "MPL-2.0",
       "devDependencies": {
         "@types/emscripten": "^1.40.1"
@@ -12092,7 +12092,7 @@
     },
     "packages/ac3": {
       "name": "@mediabunny/ac3",
-      "version": "1.38.0",
+      "version": "1.39.2",
       "license": "MPL-2.0",
       "devDependencies": {
         "@types/emscripten": "^1.40.1"
@@ -12107,7 +12107,7 @@
     },
     "packages/flac-encoder": {
       "name": "@mediabunny/flac-encoder",
-      "version": "1.38.0",
+      "version": "1.39.2",
       "license": "MPL-2.0",
       "devDependencies": {
         "@types/emscripten": "^1.40.1"
@@ -12122,7 +12122,7 @@
     },
     "packages/mp3-encoder": {
       "name": "@mediabunny/mp3-encoder",
-      "version": "1.38.0",
+      "version": "1.39.2",
       "license": "MPL-2.0",
       "devDependencies": {
         "@types/emscripten": "^1.40.1"
diff --git a/package.json b/package.json
index 669a648..4fb193f 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
   "name": "mediabunny",
   "author": "Vanilagy",
-  "version": "1.38.0",
+  "version": "1.39.2",
   "description": "Pure TypeScript media toolkit for reading, writing, and converting media files, directly in the browser.",
   "type": "module",
   "workspaces": [
diff --git a/packages/aac-encoder/package.json b/packages/aac-encoder/package.json
index 786a388..faa9753 100644
--- a/packages/aac-encoder/package.json
+++ b/packages/aac-encoder/package.json
@@ -1,7 +1,7 @@
 {
   "name": "@mediabunny/aac-encoder",
   "author": "Vanilagy",
-  "version": "1.38.0",
+  "version": "1.39.2",
   "description": "AAC encoder extension for Mediabunny, based on FFmpeg.",
   "main": "./dist/bundles/mediabunny-aac-encoder.mjs",
   "module": "./dist/bundles/mediabunny-aac-encoder.mjs",
diff --git a/packages/ac3/package.json b/packages/ac3/package.json
index de7d2d4..bd5b58c 100644
--- a/packages/ac3/package.json
+++ b/packages/ac3/package.json
@@ -1,7 +1,7 @@
 {
   "name": "@mediabunny/ac3",
   "author": "Vanilagy",
-  "version": "1.38.0",
+  "version": "1.39.2",
   "description": "AC-3 and E-AC-3 (Dolby Digital) decoder and encoder extension for Mediabunny, based on FFmpeg.",
   "main": "./dist/bundles/mediabunny-ac3.mjs",
   "module": "./dist/bundles/mediabunny-ac3.mjs",
diff --git a/packages/flac-encoder/package.json b/packages/flac-encoder/package.json
index ef0109d..fe3aac3 100644
--- a/packages/flac-encoder/package.json
+++ b/packages/flac-encoder/package.json
@@ -1,7 +1,7 @@
 {
   "name": "@mediabunny/flac-encoder",
   "author": "Vanilagy",
-  "version": "1.38.0",
+  "version": "1.39.2",
   "description": "FLAC encoder extension for Mediabunny, based on libFLAC.",
   "main": "./dist/bundles/mediabunny-flac-encoder.mjs",
   "module": "./dist/bundles/mediabunny-flac-encoder.mjs",
diff --git a/packages/mp3-encoder/package.json b/packages/mp3-encoder/package.json
index 6128c54..522f6a3 100644
--- a/packages/mp3-encoder/package.json
+++ b/packages/mp3-encoder/package.json
@@ -1,7 +1,7 @@
 {
   "name": "@mediabunny/mp3-encoder",
   "author": "Vanilagy",
-  "version": "1.38.0",
+  "version": "1.39.2",
   "description": "MP3 encoder extension for Mediabunny, based on LAME.",
   "main": "./dist/bundles/mediabunny-mp3-encoder.mjs",
   "module": "./dist/bundles/mediabunny-mp3-encoder.mjs",
diff --git a/src/conversion.ts b/src/conversion.ts
index 46fc182..298ce6b 100644
--- a/src/conversion.ts
+++ b/src/conversion.ts
@@ -515,6 +515,9 @@ export class Conversion {
 	/**
 	 * Whether this conversion, as it has been configured, is valid and can be executed. If this field is `false`, check
 	 * the `discardedTracks` field for reasons.
+	 *
+	 * Note: a conversion having discarded tracks does not automatically mean it is invalid; if the remaining, utilized
+	 * tracks make for a valid output file, the conversion is still allowed.
 	 */
 	isValid = false;
 	/** The list of tracks that are included in the output file. */
diff --git a/src/input-format.ts b/src/input-format.ts
index e7cb1a6..9a54dc3 100644
--- a/src/input-format.ts
+++ b/src/input-format.ts
@@ -542,7 +542,7 @@ export class MpegTsInputFormat extends InputFormat {
 		} else if (bytes[0] === 0x47 && bytes[TS_PACKET_SIZE + 16] === 0x47) {
 			// MPEG-TS with Forward Error Correction
 			return true;
-		} else if (bytes[4] === 0x47 && bytes[4 + TS_PACKET_SIZE] === 0x47) {
+		} else if (bytes[4] === 0x47 && bytes[4 + TS_PACKET_SIZE + 4] === 0x47) {
 			// MPEG-2-TS (DVHS)
 			return true;
 		}
diff --git a/src/media-sink.ts b/src/media-sink.ts
index dcebc04..23c4be2 100644
--- a/src/media-sink.ts
+++ b/src/media-sink.ts
@@ -529,7 +529,7 @@ export abstract class BaseMediaSampleSink<
 
 			const packetSink = this._createPacketSink();
 			const keyPacket = await packetSink.getKeyPacket(startTimestamp, { verifyKeyPackets: true })
-				?? await packetSink.getFirstKeyPacket();
+				?? await packetSink.getFirstKeyPacket({ verifyKeyPackets: true });
 
 			let currentPacket: EncodedPacket | null = keyPacket;
 
diff --git a/src/media-source.ts b/src/media-source.ts
index c3b4604..e47679b 100644
--- a/src/media-source.ts
+++ b/src/media-source.ts
@@ -1076,6 +1076,8 @@ export class MediaStreamVideoTrackSource extends VideoSource {
 	private _lastVideoFrame: VideoFrame | null = null;
 	/** @internal */
 	private _timerHandle: UnthrottledTimerHandle | null = null;
+	/** @internal */
+	private _videoElement: HTMLVideoElement | null = null;
 
 	/** A promise that rejects upon any error within this source. This promise never resolves. */
 	get errorPromise() {
@@ -1160,12 +1162,13 @@ export class MediaStreamVideoTrackSource extends VideoSource {
 			while (now - lastFrameTime > 1000 / frameRate) {
 				lastFrameTime += 1000 / frameRate;
 				const timestamp = firstVideoFrameTimestamp + frameCount / frameRate;
-				const clone = new VideoFrame(this._lastVideoFrame, {
+
+				const frame = new VideoFrame(this._videoElement ?? this._lastVideoFrame, {
 					timestamp: 1e6 * timestamp,
 					duration: 1e6 / frameRate,
 				});
 
-				addVideoFrame(clone, now);
+				addVideoFrame(frame, now);
 			}
 		};
 
@@ -1298,8 +1301,44 @@ export class MediaStreamVideoTrackSource extends VideoSource {
 				};
 
 				mediaStreamTrackProcessorWorker!.addEventListener('message', this._workerListener);
+			} else if (frameRate !== null) {
+				// No MediaStreamTrackProcessor support at all (e.g. Firefox), but we have a frame rate, so we can
+				// manually sample from a hidden <video> element instead.
+				const video = document.createElement('video');
+				video.style.position = 'fixed';
+				video.style.left = '-10000px';
+				video.style.top = '-10000px';
+				video.style.width = '1px';
+				video.style.height = '1px';
+				video.style.opacity = '0';
+				video.style.pointerEvents = 'none';
+				video.muted = true;
+				video.srcObject = new MediaStream([this._track]);
+				document.body.appendChild(video);
+				this._videoElement = video;
+
+				video.addEventListener('loadeddata', () => {
+					if (errored || !this._videoElement) {
+						return;
+					}
+
+					// This will be the first frame
+					const frame = new VideoFrame(video, {
+						timestamp: 1000 * performance.now(),
+					});
+					onVideoFrame(frame);
+					frame.close();
+				}, { once: true });
+
+				void video.play().catch((error) => {
+					errored = true;
+					this._promiseWithResolvers.reject(error);
+				});
 			} else {
-				throw new Error('MediaStreamTrackProcessor is required but not supported by this browser.');
+				throw new Error(
+					'When no explicit frame rate is set, MediaStreamTrackProcessor is required; but it\'s not supported'
+					+ ' by this browser.',
+				);
 			}
 		}
 	}
@@ -1329,6 +1368,12 @@ export class MediaStreamVideoTrackSource extends VideoSource {
 		}
 		this._lastVideoFrame?.close();
 
+		if (this._videoElement) {
+			this._videoElement.srcObject = null;
+			this._videoElement.remove();
+			this._videoElement = null;
+		}
+
 		if (this._workerTrackId !== null) {
 			assert(this._workerListener);
 
diff --git a/src/mpeg-ts/mpeg-ts-demuxer.ts b/src/mpeg-ts/mpeg-ts-demuxer.ts
index 3c03745..9e78b39 100644
--- a/src/mpeg-ts/mpeg-ts-demuxer.ts
+++ b/src/mpeg-ts/mpeg-ts-demuxer.ts
@@ -175,10 +175,10 @@ export class MpegTsDemuxer extends Demuxer {
 				// MPEG-TS with Forward Error Correction
 				this.packetOffset = 0;
 				this.packetStride = TS_PACKET_SIZE + 16;
-			} else if (startingBytes[4] === 0x47 && startingBytes[4 + TS_PACKET_SIZE] === 0x47) {
+			} else if (startingBytes[4] === 0x47 && startingBytes[4 + TS_PACKET_SIZE + 4] === 0x47) {
 				// MPEG-2-TS (DVHS)
 				this.packetOffset = 4;
-				this.packetStride = TS_PACKET_SIZE;
+				this.packetStride = TS_PACKET_SIZE + 4;
 			} else {
 				throw new Error('Unreachable.');
 			}
diff --git a/src/muxer.ts b/src/muxer.ts
index ee0e7bd..83def00 100644
--- a/src/muxer.ts
+++ b/src/muxer.ts
@@ -46,12 +46,16 @@ export abstract class Muxer {
 
 	private trackTimestampInfo = new WeakMap<OutputTrack, {
 		maxTimestamp: number;
-		maxTimestampBeforeLastKeyPacket: number;
+		maxTimestampBeforeLastKeyPacket: number | null;
 	}>();
 
 	protected validateAndNormalizeTimestamp(track: OutputTrack, timestampInSeconds: number, isKeyPacket: boolean) {
 		timestampInSeconds += track.source._timestampOffset;
 
+		if (timestampInSeconds < 0) {
+			throw new Error(`Timestamps must be non-negative (got ${timestampInSeconds}s).`);
+		}
+
 		let timestampInfo = this.trackTimestampInfo.get(track);
 		if (!timestampInfo) {
 			if (!isKeyPacket) {
@@ -60,29 +64,28 @@ export abstract class Muxer {
 
 			timestampInfo = {
 				maxTimestamp: timestampInSeconds,
-				maxTimestampBeforeLastKeyPacket: timestampInSeconds,
+				maxTimestampBeforeLastKeyPacket: null,
 			};
 			this.trackTimestampInfo.set(track, timestampInfo);
-		}
+		} else {
+			if (isKeyPacket) {
+				timestampInfo.maxTimestampBeforeLastKeyPacket = timestampInfo.maxTimestamp;
+			}
 
-		if (timestampInSeconds < 0) {
-			throw new Error(`Timestamps must be non-negative (got ${timestampInSeconds}s).`);
-		}
+			if (
+				timestampInfo.maxTimestampBeforeLastKeyPacket !== null
+				&& timestampInSeconds < timestampInfo.maxTimestampBeforeLastKeyPacket
+			) {
+				throw new Error(
+					`Timestamps cannot be smaller than the largest timestamp of the previous GOP (a GOP begins with a`
+					+ ` key packet and ends right before the next key packet). Got ${timestampInSeconds}s, but largest`
+					+ ` timestamp is ${timestampInfo.maxTimestampBeforeLastKeyPacket}s.`,
+				);
+			}
 
-		if (isKeyPacket) {
-			timestampInfo.maxTimestampBeforeLastKeyPacket = timestampInfo.maxTimestamp;
+			timestampInfo.maxTimestamp = Math.max(timestampInfo.maxTimestamp, timestampInSeconds);
 		}
 
-		if (timestampInSeconds < timestampInfo.maxTimestampBeforeLastKeyPacket) {
-			throw new Error(
-				`Timestamps cannot be smaller than the largest timestamp of the previous GOP (a GOP begins with a key`
-				+ ` packet and ends right before the next key packet). Got ${timestampInSeconds}s, but largest`
-				+ ` timestamp is ${timestampInfo.maxTimestampBeforeLastKeyPacket}s.`,
-			);
-		}
-
-		timestampInfo.maxTimestamp = Math.max(timestampInfo.maxTimestamp, timestampInSeconds);
-
 		return timestampInSeconds;
 	}
 }