3GP sample entries

Each track’s codec is named by its sample entry in stsd (see the MP4 sample tables). TS 26.244 clause 6 defines the 3GPP-specific entries below; offsets count from the start of the entry, and all numbers are big-endian.

Entries allowed in 3GP

Code	Media	Codec	Defined in
`samr`	Audio	AMR (narrowband)	TS 26.244 clause 6.5
`sawb`	Audio	AMR-WB (wideband)	TS 26.244 clause 6.5
`sawp`	Audio	AMR-WB+	TS 26.244 clause 6.9
`sevs`	Audio	EVS	TS 26.244 clause 6.14
`sivs`	Audio	IVAS	TS 26.244 clause 6.15
`mp4a`	Audio	MPEG-4 audio (AAC)	ISO/IEC 14496-14
`s263`	Video	H.263	TS 26.244 clause 6.6
`mp4v`	Video	MPEG-4 Part 2 video	ISO/IEC 14496-14
`avc1` and other AVC entries	Video	H.264	ISO/IEC 14496-15 clause 5
`hvc1`, `hev1`	Video	H.265	ISO/IEC 14496-15 clause 8
`tx3g`	Text	3GPP timed text	TS 26.245 (layout on the MOV subtitles page)
DIMS entry	Scene description	Dynamic and interactive multimedia scenes	TS 26.142
hint entries	Hint	RTP and reception hint tracks	ISO/IEC 14496-12
`3gvo`	Timed metadata	Coordination of video orientation (CVO)	TS 26.244 clause 6.11
`3glo`	Timed metadata	Location	TS 26.244 clause 6.12
`3gor`	Timed metadata	Orientation	TS 26.244 clause 6.13
quality metrics entry	Timed metadata	Quality metrics	TS 26.244 clause 16
`encv`, `enca`, `enct`	Encrypted	Protected video, audio, text	TS 26.244 clause 10.2

3GPP2 files (.3g2) also use sevc (EVRC), sqcp (13K QCELP) and ssmv (SMV), registered by 3GPP2 with object type indications 0xA0, 0xE1 and 0xA1; their layouts are in 3GPP2’s specification and are not covered here.

samr and sawb

Offset	Size	Name	Value
0	4	size	Size of the entry.
4	4	type	`samr` (AMR) or `sawb` (AMR-WB).
8	6	reserved	0.
14	2	data reference index	1-based index into `dref`.
16	8	reserved	0.
24	2	reserved	2 (the channel count position).
26	2	reserved	16 (the sample size position).
28	4	reserved	0.
32	2	time scale	Copied from the track’s `mdhd`: 8000 for AMR, 16000 for AMR-WB.
34	2	reserved	0.
36	varies	`damr`	AMR specific box (below).

The layout matches an ISO audio sample entry, with the sample rate’s integer part as a 16-bit time scale. The values 2 and 16 are fixed even for mono AMR.

damr

Offset	Size	Name	Meaning
8	4	vendor	FourCC of the encoder’s maker; informative.
12	1	decoder version	The vendor’s decoder version that best decodes the stream, or 0; informative.
13	2	mode set	Bit mask of the codec modes that may occur: bit 0 is mode 0 up to bit 8 for mode 8, numbered by the frame type (FT) field. 0x81FF means every AMR mode and comfort noise; 0x83FF every AMR-WB mode and comfort noise.
15	1	mode change period	Mode changes only every N frames; 0 means no restriction. If N is less than frames per sample, frames per sample is a multiple k × N (k ≥ 2); if greater, N is a multiple of frames per sample; if equal, each sample has one mode.
16	1	frames per sample	1 to 15 speech frames per sample (10 frames of 20 ms make a 200 ms sample). The last sample may hold fewer.

damr is a plain box: there is no version or flags. For example, mode set 0x0195 (binary 0000 0001 1001 0101) allows modes 0, 2, 4, 7 and 8.

sawp and dawp

sawp (AMR-WB+) has the same 36-byte layout as samr, with the sampling rate at offset 32, followed by a dawp box holding only a vendor FourCC (4 bytes) and a decoder version (1 byte), both informative.

s263, d263 and bitr

Offset	Size	Name	Value
4	4	type	`s263`.
8	6	reserved	0.
14	2	data reference index	1-based index into `dref`.
16	16	reserved	0.
32	2	width	Maximum width in pixels.
34	2	height	Maximum height in pixels.
36	4	reserved	0x00480000 (72 dpi horizontal).
40	4	reserved	0x00480000 (72 dpi vertical).
44	4	reserved	0.
48	2	reserved	1 (frame count).
50	32	reserved	0 (compressor name).
82	2	reserved	24 (depth).
84	2	reserved	−1.
86	varies	`d263`	H.263 specific box, in place of MP4’s `esds`.

Offset	Size	Name	Meaning (`d263`)
8	4	vendor	FourCC of the encoder’s maker; informative.
12	1	decoder version	Vendor decoder version, or 0; informative.
13	1	H263_Level	H.263 level, as in the video/H263-2000 media type (for example 10).
14	1	H263_Profile	H.263 profile (0 baseline, 3 and so on).
15	varies	`bitr`	Optional bit rate box.

Baseline H.263 is level 10, profile 0. The optional bitr box holds an average bit rate (uint32, bits per second, 0 for variable) and a maximum bit rate (uint32, over any one second).

sevs and sivs

sevs (EVS) and sivs (IVAS) use the same 36-byte audio layout: channel count at offset 24 (for IVAS, 2 for stereo or binaural and otherwise 0), 16 at offset 26, and the time scale at offset 32: 8000, 16000, 32000 or 48000 for EVS, and 16000, 32000 or 48000 for IVAS, by the widest bandwidth coded; 48000 when unknown. sevs has no child box. sivs is followed by two boxes:

Box	Contents
`ivcf`	IVAS coded format: the format category and its parameters (below).
`iver`	IVAS version: 12 reserved bits, a 4-bit specification (0 unknown, 1 fixed-point per TS 26.251, 2 floating-point per TS 26.258), then major and minor version bytes.

Category	Format
0	Unknown
1	Mono using the EVS coding modes of IVAS
2	Stereo, including binaural
3	Scene-based audio (SBA)
4	Metadata-assisted spatial audio (MASA)
5	Object-based audio (ISM)
6	Multichannel audio (MC)
7	ISM combined with MASA (OMASA)
8	ISM combined with SBA (OSBA)

The parameters are a binaural flag (stereo), a planar flag and an order of 1 to 3 (SBA), 1 to 4 objects (ISM), a CICP layout index of 6 (5.1), 12 (7.1), 14 (5.1.2), 16 (5.1.4) or 19 (7.1.4) (multichannel), and the number of MASA transport channels (0 for one, 1 for two). The exact bit layout of the ivcf structure could not be confirmed from the clause text read and is not given here.

3gvo, 3glo and 3gor

Timed metadata entries. All three have the 16-byte common header (reserved and data reference index); 3gvo adds one byte, the granularity of the rotation: 2 for CVO, 6 for high-granularity CVO, as defined in TS 26.114. 3glo (location) and 3gor (orientation) add nothing. The sample formats are in TS 26.244 clauses 14, 15 and 17 and are not covered here.

encv, enca and enct

An encrypted track replaces its sample entry type and appends a protection scheme information box (sinf, from ISO/IEC 14496-12), which records the original format:

Entry	Original formats	Contents
`encv`	`s263`, `avc1` …	Every field and box of the visual entry, then `sinf`.
`enca`	`samr`, `sawb`, `sawp`, `mp4a` …	Every field and box of the audio entry, then `sinf`.
`enct`	`tx3g` …	Every field and box of the text entry, then `sinf`.

.3GP File Format – Sample entries