diff --git a/dev/demux.html b/dev/demux.html
index 48801c4..cd9415d 100644
--- a/dev/demux.html
+++ b/dev/demux.html
@@ -29,7 +29,6 @@
 		output.start();
 
 		for await (const frame of drain.frames(0, 10)) {
-			console.log(frame.timestamp, frame.duration)
 			await mediaSource.digest(frame);
 			frame.close();
 		}
diff --git a/dev/player.html b/dev/player.html
index 50dd21b..44e6526 100644
--- a/dev/player.html
+++ b/dev/player.html
@@ -38,6 +38,8 @@ const input = new Metamuxer.Input({
 	source
 });
 
+console.log(await input.getMimeType())
+
 const videoTrack = await input.getPrimaryVideoTrack(); 
 const audioTrack = await input.getPrimaryAudioTrack(); 
 
diff --git a/src/codec.ts b/src/codec.ts
index d8e4e97..c3ad718 100644
--- a/src/codec.ts
+++ b/src/codec.ts
@@ -168,7 +168,7 @@ export const buildVideoCodecString = (codec: VideoCodec, width: number, height:
 
 		return `vp09.${profile}.${levelInfo.level.toString().padStart(2, '0')}.${bitDepth}`;
 	} else if (codec === 'av1') {
-		const profile = 0; // Main Profile
+		const profile = 0; // Main Profile, single digit
 
 		const pictureSize = width * height;
 		const levelInfo = AV1_LEVEL_TABLE.find(
@@ -273,59 +273,12 @@ export const extractVideoCodecString = (trackInfo: {
 			throw new Error('Missing AV1 codec info - unable to construct codec string.');
 		}
 
-		const profile = av1CodecInfo.seqProfile;
+		const profile = av1CodecInfo.seqProfile; // Single digit
 		const level = av1CodecInfo.seqLevelIdx0.toString().padStart(2, '0');
 		const tier = av1CodecInfo.seqTier0 ? 'H' : 'M';
 		const bitDepth = av1CodecInfo.bitDepth.toString().padStart(2, '0');
 
 		return `av01.${profile}.${level}${tier}.${bitDepth}`;
-
-		/*
-		const chunk = await videoTrack._backing.getFirstChunk({});
-		if (!chunk) {
-			throw new Error('ahh');
-		}
-
-		const buffer = new ArrayBuffer(chunk.byteLength);
-		chunk.copyTo(buffer);
-
-		console.log(new Uint8Array(buffer));
-
-		const view = new DataView(buffer);
-		let pos = 0;
-		const byte = view.getUint8(pos++);
-
-		const obuType = (byte & 0b1111000) >> 3;
-		const obuExtensionFlag = (byte & 0b100) >> 2;
-		const obuHasSizeField = (byte & 0b10) >> 1;
-
-		if (obuExtensionFlag) {
-			pos++;
-		}
-
-		function leb128() {
-			let value = 0;
-
-			for (let i = 0; i < 8; i++) {
-				const leb128_byte = view.getUint8(pos);
-				value |= (leb128_byte & 0x7f) << (i * 7); // Extract the lower 7 bits and shift them accordingly
-				pos++;
-
-				// Check if the most significant bit (MSB) is 0, signaling the end of the LEB128 sequence
-				if ((leb128_byte & 0x80) === 0) {
-					break;
-				}
-			}
-
-			return value;
-		}
-
-		if (obuHasSizeField) {
-			console.log(leb128());
-		}
-
-		// Some extra stuff, todo
-		*/
 	}
 
 	throw new TypeError(`Unhandled codec '${codec}'.`);
diff --git a/src/isobmff/isobmff-boxes.ts b/src/isobmff/isobmff-boxes.ts
index a18b513..9deb4f0 100644
--- a/src/isobmff/isobmff-boxes.ts
+++ b/src/isobmff/isobmff-boxes.ts
@@ -596,7 +596,7 @@ export const vpcC = (trackData: IsobmffVideoTrackData) => {
 	const decoderConfig = trackData.info.decoderConfig;
 	assert(decoderConfig.colorSpace); // This is guaranteed by an earlier validation step
 
-	const parts = decoderConfig.codec.split('.');
+	const parts = decoderConfig.codec.split('.'); // We can derive the required values from the codec string
 	const profile = Number(parts[1]);
 	const level = Number(parts[2]);
 
@@ -604,10 +604,15 @@ export const vpcC = (trackData: IsobmffVideoTrackData) => {
 	const chromaSubsampling = 0;
 	const thirdByte = (bitDepth << 4) + (chromaSubsampling << 1) + Number(decoderConfig.colorSpace.fullRange);
 
-	// Set all to undetermined. We could determine them using the codec color space info, but there's no need.
-	const colourPrimaries = 2;
-	const transferCharacteristics = 2;
-	const matrixCoefficients = 2;
+	const colourPrimaries = decoderConfig.colorSpace.primaries
+		? COLOR_PRIMARIES_MAP[decoderConfig.colorSpace.primaries]
+		: 2; // Default to undetermined
+	const transferCharacteristics = decoderConfig.colorSpace.transfer
+		? TRANSFER_CHARACTERISTICS_MAP[decoderConfig.colorSpace.transfer]
+		: 2;
+	const matrixCoefficients = decoderConfig.colorSpace.matrix
+		? MATRIX_COEFFICIENTS_MAP[decoderConfig.colorSpace.matrix]
+		: 2;
 
 	return fullBox('vpcC', 1, 0, [
 		u8(profile), // Profile
@@ -621,21 +626,45 @@ export const vpcC = (trackData: IsobmffVideoTrackData) => {
 };
 
 /** AV1 Configuration Box: Provides additional information to the decoder. */
-export const av1C = () => {
+export const av1C = (trackData: IsobmffVideoTrackData) => {
 	// Reference: https://aomediacodec.github.io/av1-isobmff/
 
+	const decoderConfig = trackData.info.decoderConfig;
+	const parts = decoderConfig.codec.split('.'); // We can derive the required values from the codec string
+
 	const marker = 1;
 	const version = 1;
 	const firstByte = (marker << 7) + version;
 
-	// The box contents are not correct like this, but its length is. Getting the values for the last three bytes
-	// requires peeking into the bitstream of the coded chunks. Might come back later.
-	// TODO
+	const profile = Number(parts[1]);
+	const levelAndTier = parts[2]!;
+	const level = Number(levelAndTier.slice(0, -1));
+	const tier = levelAndTier.slice(-1) === 'H' ? 1 : 0;
+	const bitDepth = Number(parts[3]);
+	const secondByte = (profile << 5) + level;
+
+	// The following values are educated, very likely guesses (typical 4:2:0 chroma subsampling)
+	const twelveBit = 0;
+	const monochrome = 0;
+	const chromaSubsamplingX = 1;
+	const chromaSubsamplingY = 1;
+	const chromaSamplePosition = 1; // CSP_VERTICAL
+	const thirdByte = (tier << 7)
+		+ ((bitDepth === 8 ? 0 : 1) << 6)
+		+ (twelveBit << 5)
+		+ (monochrome << 4)
+		+ (chromaSubsamplingX << 3)
+		+ (chromaSubsamplingY << 2)
+		+ chromaSamplePosition;
+
+	const initialPresentationDelayPresent = 0; // Should be fine
+	const fourthByte = initialPresentationDelayPresent;
+
 	return box('av1C', [
 		firstByte,
-		0,
-		0,
-		0,
+		secondByte,
+		thirdByte,
+		fourthByte,
 	]);
 };