Add getMimeType to Output & other small adjustments

src/isobmff/isobmff-misc.ts

@@ -0,0 +1,21 @@
+export const buildIsobmffMimeType = (info: {
+	isQuicktime: boolean;
+	hasVideo: boolean;
+	hasAudio: boolean;
+	codecStrings: string[];
+}) => {
+	const base = info.hasVideo
+		? 'video/'
+		: info.hasAudio
+			? 'audio/'
+			: 'application/';
+
+	let string = base + (info.isQuicktime ? 'quicktime' : 'mp4');
+
+	if (info.codecStrings.length > 0) {
+		const uniqueCodecMimeTypes = [...new Set(info.codecStrings)];
+		string += `; codecs="${uniqueCodecMimeTypes.join(', ')}"`;
+	}
+
+	return string;
+};