diff --git a/src/input-format.ts b/src/input-format.ts
index 515ec9e..cc7e8aa 100644
--- a/src/input-format.ts
+++ b/src/input-format.ts
@@ -35,7 +35,7 @@ export abstract class InputFormat {
 export abstract class IsobmffInputFormat extends InputFormat {
 	/** @internal */
 	protected async _getMajorBrand(input: Input) {
-		const sourceSize = await input._mainReader.source._getSize();
+		const sourceSize = await input._mainReader.source.getSize();
 		if (sourceSize < 12) {
 			return null;
 		}
@@ -104,7 +104,7 @@ export class QuickTimeInputFormat extends IsobmffInputFormat {
 export class MatroskaInputFormat extends InputFormat {
 	/** @internal */
 	protected async isSupportedEBMLOfDocType(input: Input, desiredDocType: string) {
-		const sourceSize = await input._mainReader.source._getSize();
+		const sourceSize = await input._mainReader.source.getSize();
 		if (sourceSize < 8) {
 			return false;
 		}
@@ -209,7 +209,7 @@ export class WebMInputFormat extends MatroskaInputFormat {
 export class Mp3InputFormat extends InputFormat {
 	/** @internal */
 	async _canReadInput(input: Input) {
-		const sourceSize = await input._mainReader.source._getSize();
+		const sourceSize = await input._mainReader.source.getSize();
 		if (sourceSize < 4) {
 			return false;
 		}
@@ -274,7 +274,7 @@ export class Mp3InputFormat extends InputFormat {
 export class WaveInputFormat extends InputFormat {
 	/** @internal */
 	async _canReadInput(input: Input) {
-		const sourceSize = await input._mainReader.source._getSize();
+		const sourceSize = await input._mainReader.source.getSize();
 		if (sourceSize < 12) {
 			return false;
 		}
@@ -311,7 +311,7 @@ export class WaveInputFormat extends InputFormat {
 export class OggInputFormat extends InputFormat {
 	/** @internal */
 	async _canReadInput(input: Input) {
-		const sourceSize = await input._mainReader.source._getSize();
+		const sourceSize = await input._mainReader.source.getSize();
 		if (sourceSize < 4) {
 			return false;
 		}
diff --git a/src/input.ts b/src/input.ts
index ad022c4..8a12fc2 100644
--- a/src/input.ts
+++ b/src/input.ts
@@ -8,20 +8,20 @@ import { Source } from './source';
  * The options for creating an Input object.
  * @public
  */
-export type InputOptions = {
+export type InputOptions<S extends Source = Source> = {
 	/** A list of supported formats. If the source file is not of one of these formats, then it cannot be read. */
 	formats: InputFormat[];
 	/** The source from which data will be read. */
-	source: Source;
+	source: S;
 };
 
 /**
  * Represents an input media file. This is the root object from which all media read operations start.
  * @public
  */
-export class Input {
+export class Input<S extends Source = Source> {
 	/** @internal */
-	_source: Source;
+	_source: S;
 	/** @internal */
 	_formats: InputFormat[];
 	/** @internal */
@@ -31,7 +31,7 @@ export class Input {
 	/** @internal */
 	_format: InputFormat | null = null;
 
-	constructor(options: InputOptions) {
+	constructor(options: InputOptions<S>) {
 		if (!options || typeof options !== 'object') {
 			throw new TypeError('options must be an object.');
 		}
@@ -64,6 +64,14 @@ export class Input {
 		})();
 	}
 
+	/**
+	 * Returns the source from which this input file reads its data. This is the same source that was passed to the
+	 * constructor.
+	 */
+	get source() {
+		return this._source;
+	}
+
 	/**
 	 * Returns the format of the input file. You can compare this result directly to the InputFormat singletons or use
 	 * `instanceof` checks for subset-aware logic (for example, `format instanceof MatroskaInputFormat` is true for
diff --git a/src/isobmff/isobmff-demuxer.ts b/src/isobmff/isobmff-demuxer.ts
index 7dc3a9a..87e2573 100644
--- a/src/isobmff/isobmff-demuxer.ts
+++ b/src/isobmff/isobmff-demuxer.ts
@@ -198,7 +198,7 @@ export class IsobmffDemuxer extends Demuxer {
 		super(input);
 
 		this.metadataReader = new IsobmffReader(input._mainReader);
-		this.chunkReader = new IsobmffReader(new Reader(input._source, 64 * 2 ** 20)); // Max 64 MiB of stored chunks
+		this.chunkReader = new IsobmffReader(new Reader(input.source, 64 * 2 ** 20)); // Max 64 MiB of stored chunks
 	}
 
 	override async computeDuration() {
@@ -235,7 +235,7 @@ export class IsobmffDemuxer extends Demuxer {
 
 	readMetadata() {
 		return this.metadataPromise ??= (async () => {
-			const sourceSize = await this.metadataReader.reader.source._getSize();
+			const sourceSize = await this.metadataReader.reader.source.getSize();
 
 			while (this.metadataReader.pos < sourceSize) {
 				await this.metadataReader.reader.loadRange(
@@ -2191,7 +2191,7 @@ abstract class IsobmffTrackBacking implements InputTrackBacking {
 			}
 
 			const metadataReader = demuxer.metadataReader;
-			const sourceSize = await metadataReader.reader.source._getSize();
+			const sourceSize = await metadataReader.reader.source.getSize();
 
 			let prevFragment: Fragment | null = null;
 			let bestFragmentIndex = fragmentIndex;
diff --git a/src/matroska/matroska-demuxer.ts b/src/matroska/matroska-demuxer.ts
index c2afde4..d7be74f 100644
--- a/src/matroska/matroska-demuxer.ts
+++ b/src/matroska/matroska-demuxer.ts
@@ -165,7 +165,7 @@ export class MatroskaDemuxer extends Demuxer {
 		this.metadataReader = new EBMLReader(input._mainReader);
 
 		// Max 64 MiB of stored clusters
-		this.clusterReader = new EBMLReader(new Reader(input._source, 64 * 2 ** 20));
+		this.clusterReader = new EBMLReader(new Reader(input.source, 64 * 2 ** 20));
 	}
 
 	override async computeDuration() {
@@ -211,7 +211,7 @@ export class MatroskaDemuxer extends Demuxer {
 		return this.readMetadataPromise ??= (async () => {
 			this.metadataReader.pos = 0;
 
-			const fileSize = await this.input._source._getSize();
+			const fileSize = await this.input.source.getSize();
 
 			while (this.metadataReader.pos < fileSize - MIN_HEADER_SIZE) {
 				await this.metadataReader.reader.loadRange(
@@ -258,7 +258,7 @@ export class MatroskaDemuxer extends Demuxer {
 
 			dataStartPos: segmentDataStart,
 			elementEndPos: dataSize === -1
-				? (await this.input._source._getSize() - MIN_HEADER_SIZE)
+				? (await this.input.source.getSize() - MIN_HEADER_SIZE)
 				: segmentDataStart + dataSize,
 			clusterSeekStartPos: segmentDataStart,
 
diff --git a/src/mp3/mp3-demuxer.ts b/src/mp3/mp3-demuxer.ts
index 83a519d..ba9f16c 100644
--- a/src/mp3/mp3-demuxer.ts
+++ b/src/mp3/mp3-demuxer.ts
@@ -32,7 +32,7 @@ export class Mp3Demuxer extends Demuxer {
 
 	async readMetadata() {
 		return this.metadataPromise ??= (async () => {
-			const fileSize = await this.input._source._getSize();
+			const fileSize = await this.input.source.getSize();
 			this.reader.fileSize = fileSize;
 
 			// Just load the entire file. Primitive, but the only way to actually ensure 100% correct timestamps.
diff --git a/src/ogg/ogg-demuxer.ts b/src/ogg/ogg-demuxer.ts
index a9045d9..3626400 100644
--- a/src/ogg/ogg-demuxer.ts
+++ b/src/ogg/ogg-demuxer.ts
@@ -38,12 +38,12 @@ export class OggDemuxer extends Demuxer {
 		super(input);
 
 		// We don't need a persistent metadata reader as we read all metadata once at the start and then never again
-		this.reader = new OggReader(new Reader(input._source, 64 * 2 ** 20));
+		this.reader = new OggReader(new Reader(input.source, 64 * 2 ** 20));
 	}
 
 	async readMetadata() {
 		return this.metadataPromise ??= (async () => {
-			this.fileSize = await this.input._source._getSize();
+			this.fileSize = await this.input.source.getSize();
 
 			while (this.reader.pos < this.fileSize - MIN_PAGE_HEADER_SIZE) {
 				await this.reader.reader.loadRange(
diff --git a/src/reader.ts b/src/reader.ts
index 88a8ac4..4f720a6 100644
--- a/src/reader.ts
+++ b/src/reader.ts
@@ -25,7 +25,7 @@ export class Reader {
 	constructor(public source: Source, public maxStorableBytes = Infinity) {}
 
 	async loadRange(start: number, end: number) {
-		end = Math.min(end, await this.source._getSize());
+		end = Math.min(end, await this.source.getSize());
 
 		if (start >= end) {
 			return;
diff --git a/src/source.ts b/src/source.ts
index 854532a..390ed7e 100644
--- a/src/source.ts
+++ b/src/source.ts
@@ -13,8 +13,11 @@ export abstract class Source {
 	/** @internal */
 	_sizePromise: Promise<number> | null = null;
 
-	/** @internal */
-	_getSize() {
+	/**
+	 * Resolves with the total size of the file in bytes. This function is memoized, meaning only the first call
+	 * will retrieve the size.
+	 */
+	getSize() {
 		return this._sizePromise ??= this._retrieveSize();
 	}
 
diff --git a/src/wave/wave-demuxer.ts b/src/wave/wave-demuxer.ts
index 79b1167..53ec8f0 100644
--- a/src/wave/wave-demuxer.ts
+++ b/src/wave/wave-demuxer.ts
@@ -37,7 +37,7 @@ export class WaveDemuxer extends Demuxer {
 		super(input);
 
 		this.metadataReader = new RiffReader(input._mainReader);
-		this.chunkReader = new RiffReader(new Reader(input._source, 64 * 2 ** 20));
+		this.chunkReader = new RiffReader(new Reader(input.source, 64 * 2 ** 20));
 	}
 
 	async readMetadata() {
diff --git a/todo.txt b/todo.txt
index 3f5dfc6..43ab60d 100644
--- a/todo.txt
+++ b/todo.txt
@@ -1,4 +1,5 @@
 - https://github.com/Vanilagy/mp4-muxer/issues/83 tell him it's possible now
 - cross-track offset for streaming sources
 - textsubtitlesource, chunked piping
-- More efficient MP3 loading when reading sequentially
\ No newline at end of file
+- More efficient MP3 loading when reading sequentially
+- Validate types returned by custom coders
\ No newline at end of file