pkg/description

Session and Media types that describe RTSP stream metadata.

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

Session

A Session is the top-level description of an RTSP stream. It maps directly to an SDP session description and holds one or more Media entries.

type Session struct {
    BaseURL      *base.URL
    Title        string
    Multicast    bool
    KeyMgmtMikey *mikey.Message
    FECGroups    []SessionFECGroup
    Medias       []*Media
}

Fields

BaseURL · *base.URL

Base URL of the stream. Populated when the session is received from a server; read-only.

Title · string

Optional human-readable title of the stream. Maps to the SDP s= field.

Multicast · bool

When true, the SDP connection address is set to a multicast address (224.1.0.0).

KeyMgmtMikey · *mikey.Message

Optional MIKEY key-management attribute (a=key-mgmt). Used for SRTP streams.

FECGroups · []SessionFECGroup

Forward Error Correction groups as defined in RFC 5109. Each group is a slice of media IDs.

Medias · []*Media · required

The list of media streams in this session. At least one entry is required for a valid SDP.

Methods

FindFormat

func (d *Session) FindFormat(forma any) *Media

Searches all medias in the session for a format of the given type. When found, it stores the format in forma (a pointer to the target format variable) and returns the owning *Media. Returns nil if no matching format is found.

var forma *format.H264
media := desc.FindFormat(&forma)
if media != nil {
    // forma is now populated
}

Marshal

func (d Session) Marshal() ([]byte, error)

Encodes the session as an SDP byte slice.

Unmarshal

func (d *Session) Unmarshal(ssd *sdp.SessionDescription) error

Decodes the session from a parsed SDP session description.

---

Media

A Media represents a single media stream (e.g., one video track or one audio track) within a session.

type Media struct {
    Type          MediaType
    ID            string
    IsBackChannel bool
    Profile       headers.TransportProfile
    KeyMgmtMikey  *mikey.Message
    Control       string
    Formats       []format.Format
}

Fields

Type · MediaType · required

The type of this media stream: MediaTypeVideo, MediaTypeAudio, or MediaTypeApplication.

ID · string

Optional media identifier (a=mid). Must be alphanumeric. Used when multiple media sections are bundled (RFC 5888).

IsBackChannel · bool

When true, the media is a back channel (e.g., two-way audio on an IP camera). Serialized as a=sendonly in SDP.

Profile · headers.TransportProfile

The RTP profile: TransportProfileAVP (default) or TransportProfileSAVP (for SRTP).

KeyMgmtMikey · *mikey.Message

Optional per-media MIKEY key-management attribute.

Control · string

The a=control attribute value. Used to build the per-media RTSP URL for SETUP requests.

Formats · []format.Format · required

The RTP payload formats carried by this media stream. At least one format is required.

Methods

FindFormat

func (m Media) FindFormat(forma any) bool

Searches the media’s Formats slice for a format whose concrete type matches the element type of forma. On success, sets *forma and returns true.

URL

func (m Media) URL(contentBase *base.URL) (*base.URL, error)

Returns the absolute RTSP URL for this media, resolved against contentBase (the Content-Base header from the server). Returns an error when contentBase is nil.

Marshal

func (m Media) Marshal() (*psdp.MediaDescription, error)

Encodes the media as a pion SDP MediaDescription.

Unmarshal

func (m *Media) Unmarshal(md *psdp.MediaDescription) error

Decodes the media from a pion SDP MediaDescription.

---

MediaType

MediaType is a string type used to classify a media stream.

Constant	Value	Description
MediaTypeVideo	"video"	Video stream
MediaTypeAudio	"audio"	Audio stream
MediaTypeApplication	"application"	Application data stream (e.g., metadata, KLV)

---

SessionFECGroup

type SessionFECGroup []string

A SessionFECGroup is a slice of media IDs that form a Forward Error Correction group (RFC 5109). Groups are serialized as a=group:FEC <id1> <id2> ... in SDP.

---

Code example

Building a session description for a recording client that sends H.264 video:

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

desc := &description.Session{
    Medias: []*description.Media{
        {
            Type: description.MediaTypeVideo,
            Formats: []format.Format{
                &format.H264{
                    PayloadTyp:        96,
                    PacketizationMode: 1,
                },
            },
        },
    },
}

Searching for a specific format across all medias:

var h264Fmt *format.H264
media := desc.FindFormat(&h264Fmt)
if media == nil {
    // no H264 track found
}