This section documents various codes used in the file format; handler codes (that declare track types) and group types (as used in the AVC specification) in particular.

Code	Abstract	Type	Defined in/by
3gag	Text track3GPP PSS Annex G video buffer parameters	group	3GPP
3gsd	3GPP Scene Description	handler	3GPP
ID32	ID3 version 2 meta-data handler (meta box)	handler	inline
avcb	AVC HRD parameters	group	3GPP
avll	AVC layer description group	group	AVC
avss	AVC Sub-sequence group	group	AVC
crsm	ClockReferenceStream	handler	MPEG-4
fdsm	Font data streams (defined in part MPEG-4 part 18)	handler	MPEG-4
gesm	General MPEG-4 systems streams (without specific handler)	handler	see (1) below
hint	Hint track	handler	ISO
ipsm	IPMP Stream	handler	MPEG-4
meta	Meta-data streams	handler	MPEG-4
m7sm	MPEG7Stream	handler	MPEG-4
mjsm	MPEG-J Stream	handler	MPEG-4
mp21	MPEG-21 Digital item	handler	MPEG-21
ocsm	ObjectContentInfoStream	handler	MPEG-4
odkm	OMA DRM KMS protection scheme	protection scheme type	OMA DRM 2.0
odsm	ObjectDescriptorStream	handler	MPEG-4
roll	Pre/Post roll group	group	AVC, ISO
sdsm	SceneDescriptionStream	handler	MPEG-4
soun	Audio track	handler	ISO
text	Text track	handler	3GPP
vide	Video track	handler	ISO

1. There only exists a defined set of handler code-points in MP4 file format allowing declaration of most known MPEG-4 Systems streams. However there is no provision for private MPEG-4 streams, which may be used by the file creator. This will likely push the file creator into using one of the defined handler types, which is wrong and may corrupt processing by some file readers. This is a generic handler type to indicate that the media is an MPEG-4 systems stream, without further details on the stream type itself. The associated sample descriptions must still remain the same, i.e. "mp4s" as used with all MPEG-4 systems streams.