pkg/format

RTP payload format types with encoders and decoders.

Import path: github.com/bluenviron/gortsplib/v5/pkg/format

Format interface

Every RTP payload format implements the Format interface:

type Format interface {
    // ClockRate returns the RTP clock rate in Hz.
    ClockRate() int

    // PayloadType returns the RTP payload type number.
    PayloadType() uint8

    // RTPMap returns the rtpmap SDP attribute value (e.g. "H264/90000").
    RTPMap() string

    // FMTP returns the fmtp SDP attribute as a key-value map.
    FMTP() map[string]string

    // PTSEqualsDTS reports whether PTS equals DTS for the given RTP packet.
    // Used to determine whether a packet carries a random-access point.
    PTSEqualsDTS(*rtp.Packet) bool

    // Codec returns a human-readable codec name.
    // Deprecated: arbitrary. Will be removed in the next version.
    Codec() string
}

Method descriptions

ClockRate · int

The RTP clock rate in Hz used for timestamp calculations. For example, 90000 for video formats and 48000 for Opus audio.

PayloadType · uint8

The RTP payload type number (0–127). Dynamic payload types are in the range 96–127. Some formats use static payload type numbers (e.g., PCMU is 0, PCMA is 8).

RTPMap · string

The a=rtpmap SDP attribute value. Returns an empty string for formats with static payload types where rtpmap is optional.

FMTP · map[string]string

The a=fmtp attribute as a parsed key-value map. Returns an empty map when no format parameters are needed.

PTSEqualsDTS · bool

Reports whether the presentation timestamp equals the decode timestamp for the given packet. Returns true on random-access points (e.g., H.264 IDR frames).

---

Format implementations

Struct	Codec	Static payload type	Dynamic (96–127)	Encoder pkg	Decoder pkg
H264	H.264 / AVC	35 (allowed)	Yes	rtph264	rtph264
H265	H.265 / HEVC	—	Yes	rtph265	rtph265
AV1	AV1	—	Yes	rtpav1	rtpav1
VP9	VP9	—	Yes	rtpvp9	rtpvp9
VP8	VP8	—	Yes	rtpvp8	rtpvp8
MPEG4Video	MPEG-4 Part 2 video	—	Yes	—	—
MPEG1Video	MPEG-1/2 video	32	No	rtpmpeg1video	rtpmpeg1video
MJPEG	Motion JPEG	26	No	rtpmjpeg	rtpmjpeg
Opus	Opus / MultiOpus	—	Yes	rtpsimpleaudio	rtpsimpleaudio
MPEG4Audio	MPEG-4 Audio (Generic)	—	Yes	rtpmpeg4audio	rtpmpeg4audio
MPEG4AudioLATM	MPEG-4 Audio LATM	—	Yes	—	—
Vorbis	Vorbis	—	Yes	—	—
AC3	AC-3	—	Yes	rtpac3	rtpac3
G711	G.711 PCMU/PCMA	0, 8	Yes	rtpsimpleaudio	rtpsimpleaudio
G722	G.722	9	No	rtpsimpleaudio	rtpsimpleaudio
G726	G.726 (16/24/32/40 kbps)	—	Yes	—	—
LPCM	Linear PCM (L8/L16/L24)	10, 11	Yes	rtplpcm	rtplpcm
MPEG1Audio	MPEG-1/2 audio	14	No	rtpmpeg1audio	rtpmpeg1audio
Speex	Speex	—	Yes	—	—
KLV	SMPTE 336M KLV	—	Yes	rtpklv	rtpklv
MPEGTS	MPEG-TS	33	No	rtpmpegts	rtpmpegts
Generic	Unknown / fallback	any	any	—	—

---

Encoder and decoder pattern

Formats that carry complex framing (e.g., H.264 NAL unit packetization) provide CreateEncoder() and CreateDecoder() factory methods. These return codec-specific types from sub-packages under pkg/format/rtp<codec>.

Encoding

encode, err := forma.CreateEncoder()
if err != nil { ... }

// Encode an access unit ([][]byte for H.264) into RTP packets
pkts, err := enc.Encode(accessUnit)
if err != nil { ... }

for _, pkt := range pkts {
    // send pkt over the network
}

Decoding

dec, err := forma.CreateDecoder()
if err != nil { ... }

// Decode a single RTP packet into an access unit
au, pts, err := dec.Decode(pkt)
if err != nil { ... }
// use au ([][]byte for H.264)

---

H264 struct

H264 is the RTP format for the H.264 codec (RFC 6184).

type H264 struct {
    PayloadTyp        uint8
    SPS               []byte
    PPS               []byte
    PacketizationMode int
}

PayloadTyp · uint8 · required

RTP payload type number. Typically 96 for dynamic assignment. The field name is PayloadTyp (not PayloadType) to avoid a collision with the interface method.

SPS · []byte

H.264 Sequence Parameter Set NAL unit (without Annex B start code). Serialized into the sprop-parameter-sets fmtp attribute.

PPS · []byte

H.264 Picture Parameter Set NAL unit (without Annex B start code). Serialized alongside SPS in sprop-parameter-sets.

PacketizationMode · int

H.264 packetization mode (0 = single NAL unit mode, 1 = non-interleaved mode). Serialized as the packetization-mode fmtp attribute. Defaults to 0.

H264 methods

Method	Signature	Description
CreateEncoder	() (*rtph264.Encoder, error)	Returns an H.264 RTP encoder initialized with the format’s payload type and packetization mode.
CreateDecoder	() (*rtph264.Decoder, error)	Returns an H.264 RTP decoder.
SafeSetParams	(sps []byte, pps []byte)	Thread-safe setter for SPS and PPS parameters.
SafeParams	() ([]byte, []byte)	Thread-safe getter for SPS and PPS parameters.

---

Example with H264

import (
    "github.com/bluenviron/gortsplib/v5/pkg/format"
    "github.com/bluenviron/gortsplib/v5/pkg/format/rtph264"
)

// Declare the format
forma := &format.H264{
    PayloadTyp:        96,
    PacketizationMode: 1,
}

// Encoding
enc, err := forma.CreateEncoder()
if err != nil { ... }

// accessUnit is a [][]byte of H.264 NAL units
pkts, err := enc.Encode(accessUnit)
if err != nil { ... }

// Decoding
dec, err := forma.CreateDecoder()
if err != nil { ... }

au, pts, err := dec.Decode(pkt)
if err != nil { ... }

---

Codec-specific encoder/decoder packages

Each sub-package under pkg/format/rtp<codec> exposes Encoder and Decoder structs with codec-specific options:

Sub-package	Codec
pkg/format/rtph264	H.264
pkg/format/rtph265	H.265
pkg/format/rtpav1	AV1
pkg/format/rtpvp8	VP8
pkg/format/rtpvp9	VP9
pkg/format/rtpmpeg4audio	MPEG-4 Audio
pkg/format/rtpac3	AC-3
pkg/format/rtplpcm	Linear PCM
pkg/format/rtpklv	KLV
pkg/format/rtpmjpeg	Motion JPEG
pkg/format/rtpmpeg1audio	MPEG-1 Audio
pkg/format/rtpmpeg1video	MPEG-1 Video
pkg/format/rtpmpegts	MPEG-TS
pkg/format/rtpsimpleaudio	G.711, G.722, Opus

The rtpfragmented sub-package provides a generic fragmented-unit encoder/decoder used internally by several codec packages.