Add fastStart: 'reserve' option (closes #119)

src/isobmff/isobmff-boxes.ts

@@ -330,17 +330,17 @@ export const ftyp = (details: {
 /** Movie Sample Data Box. Contains the actual frames/samples of the media. */
 export const mdat = (reserveLargeSize: boolean): Box => ({ type: 'mdat', largeSize: reserveLargeSize });
 
+/** Free Space Box: A box that designates unused space in the movie data file. */
+export const free = (size: number): Box => ({ type: 'free', size });
+
 /**
  * Movie Box: Used to specify the information that defines a movie - that is, the information that allows
  * an application to interpret the sample data that is stored elsewhere.
  */
-export const moov = (
-	muxer: IsobmffMuxer,
-	fragmented = false,
-) => box('moov', undefined, [
+export const moov = (muxer: IsobmffMuxer) => box('moov', undefined, [
 	mvhd(muxer.creationTime, muxer.trackDatas),
 	...muxer.trackDatas.map(x => trak(x, muxer.creationTime)),
-	fragmented ? mvex(muxer.trackDatas) : null,
+	muxer.isFragmented ? mvex(muxer.trackDatas) : null,
 	udta(muxer),
 ]);