MP4文件Boxes的层次结构

MP4文件的基本组成单元是box，也就是说MP4文件是由各种各样的box组成的，有parent box，还有children box。因此，这些boxes之间存在一定的层次关系，总结如下表所示，表中标记出了各个box必选或可选特性，√代表Box必选。

ftyp						√	file type and compatibility
pdin							progressive download information
moov						√	container for all the metadata
	mvhd					√	movie header, overall declarations
	trak					√	container for an individual track or stream
		tkhd				√	track header, overall information about the track
		tref					track reference container
		edts					edit list container
			elst				an edit list
		mdia				√	container for the media information in a track
			mdhd			√	media header, overall information about the media
			hdlr			√	handler, declares the media (handler) type
			minf			√	media information container
				vmhd			video media header, overall information (video track only)
				smhd			sound media header, overall information (sound track only)
				hmhd			hint media header, overall information (hint track only)
				nmhd			Null media header, overall information (some tracks only)
				dinf		√	data information box, container
					dref	√	data reference box, declares source(s) of media data in track
				stbl		√	sample table box, container for the time/space map
					stsd	√	sample descriptions (codec types, initialization etc.)
					stts	√	(decoding) time-to-sample
					ctts		(composition) time to sample
					stsc	√	sample-to-chunk, partial data-offset information
					stsz		sample sizes (framing)
					stz2		compact sample sizes (framing)
					stco	√	chunk offset, partial data-offset information
					co64		64-bit chunk offset
					stss		sync sample table (random access points)
					stsh		shadow sync sample table
					padb		sample padding bits
					stdp		sample degradation priority
					sdtp		independent and disposable samples
					sbgp		sample-to-group
					sgpd		sample group description
					subs		sub-sample information
	mvex						movie extends box
		mehd					movie extends header box
		trex				√	track extends defaults
	ipmc						IPMP Control Box
moof							movie fragment
	mfhd					√	movie fragment header
	traf						track fragment
		tfhd				√	track fragment header
		trun					track fragment run
		sdtp					independent and disposable samples
		sbgp					sample-to-group
		subs					sub-sample information
mfra							movie fragment random access
	tfra						track fragment random access
	mfro					√	movie fragment random access offset
mdat							media data container
free							free space
skip							free space
	udta						user-data
		cprt					copyright etc.
meta							metadata
	hdlr					√	handler, declares the metadata (handler) type
	dinf						data information box, container
		dref					data reference box, declares source(s) of metadata items
	ipmc						IPMP Control Box
	iloc						item location
	ipro						item protection
		sinf					protection scheme information box
			frma				original format box
			imif				IPMP Information box
			schm				scheme type box
			schi				scheme information box
	iinf						item information
	xml						XML container
	bxml						binary XML container
	pitm						primary item reference
	fiin						file delivery item information
		paen					partition entry
			fpar				file partition
			fecr				FEC reservoir
		segr					file delivery session group
		gitn					group id to name
		tsel					track selection
meco							additional metadata container
	mere						metabox relation