Start work on demuxing

src/demuxer.ts

@@ -0,0 +1,14 @@
+import { Input } from './input';
+import { InputTrack } from './input-track';
+
+export abstract class Demuxer {
+	input: Input;
+
+	constructor(input: Input) {
+		this.input = input;
+	}
+
+	abstract getDuration(): Promise<number>;
+	abstract getTracks(): Promise<InputTrack[]>;
+	abstract getMimeType(): Promise<string>;
+}