librtmp2

A modern, open-source Rust library for Legacy RTMP and Enhanced RTMP v1/v2.

Overview

librtmp2 is a Rust RTMP protocol library: handshake, chunking, AMF commands, live publish/play relay, and an extern "C" FFI layer. It is meant to be embedded in custom servers, clients, and relay tools.

What it is good at today:

Live ingest and relay for OBS/FFmpeg-style workflows (H.264/AAC and Enhanced-RTMP passthrough for HEVC/AV1)
Minimal RTMP server and client (connect → createStream → publish / play)
RTMPS (RTMP over TLS) via the optional tls Cargo feature (OpenSSL), enabled by default
Parser/serializer modules for E-RTMP v1/v2 structures (usable from embedders; not all are wired into the session layer yet)

What it is not:

Not a complete Adobe RTMP 1.0 implementation (no VOD commands, encrypted handshake, etc.; AMF3 shared object envelopes are parsed/delivered, but multi-client attribute sync/persistence is left to the host)
Not a full E-RTMP v2 session stack (capsEx negotiation, multitrack, ModEx, and the reconnect-request handshake are wired into the session; the actual reconnect-redirect transport logic is left to the host application)
Not an HTTP server, media policy layer, or FFmpeg wrapper

See Implementation status for the code-accurate breakdown.

Architecture

OBS / FFmpeg / App
        │
        ▼
      librtmp2          ← this library
      ├── Handshake / Chunking / Control
      ├── AMF0 commands (connect, publish, play, …)
      ├── Session relay (publisher → players)
      ├── ertmp/ + flv/ parsers (library modules)
      └── RTMPS transport (optional)

The live path is implemented in session/conn.rs and server/mod.rs. Parser modules under ertmp/ and flv/ can be used directly by embedders even when they are not yet called from the default session flow.

State Machine

TCP_ACCEPTED
  → HANDSHAKE
  → CONNECTED
  → [CAPS_NEGOTIATED]      ← entered when connect advertises E-RTMP v2 caps
  → APP_CONNECTED
  → STREAM_CREATED
  → PUBLISHING | PLAYING
  → CLOSING
  → CLOSED

CAPS_NEGOTIATED is entered when the client's connect command advertises fourCcList / capsEx / videoFourCcInfoMap / reconnect; negotiate_caps() computes the response and the negotiated caps are echoed back in the connect _result (session/conn.rs). Clients that don't advertise v2 caps skip straight to APP_CONNECTED as before.

Build

# Debug build
cargo build

# Release build
cargo build --release

# Run tests
cargo test

# Build without TLS (no OpenSSL dependency)
cargo build --no-default-features

The crate uses crate-type = ["cdylib", "staticlib", "lib"] and produces:

librtmp2.so / librtmp2.dll — cdylib for FFI consumers
librtmp2.a / librtmp2.lib — staticlib for FFI consumers
Rust lib — for direct Cargo dependency

TLS / RTMPS

RTMPS (RTMP over TLS) is supported via OpenSSL and is enabled by default via the tls Cargo feature. To produce a plaintext-only build without the optional TLS/OpenSSL dependency:

cargo build --no-default-features

Call lrtmp2_tls_supported() at runtime to check whether the library was built with TLS.

Using as a Rust Crate

Add to your Cargo.toml:

[dependencies]
librtmp2 = { path = "../librtmp2" }

Without TLS:

[dependencies]
librtmp2 = { path = "../librtmp2", default-features = false }

External media export / inject (Rust)

Integrators can observe or feed the same local relay path used by publishers and players — without sockets or cluster concepts:

use librtmp2::server::{
    is_external_publisher_id, Server, StreamInitSnapshot, EXTERNAL_RELAY_PUBLISHER_ID,
};
use librtmp2::{FrameType, RelayFrame, ServerConfig};

// Bounded export of publisher frames (disabled by default = no clones).
server.enable_relay_export(/*max_frames*/ 256, /*max_bytes*/ 4 * 1024 * 1024);
let frames: Vec<RelayFrame> = server.drain_exported_relay_frames();

// Socket-less inject into cache + player fan-out for (app, stream).
// Claims the route until `release_injected_route` (call when the feed ends).
// Required for continually changing routes — otherwise new claims stop at
// `MAX_EXTERNAL_PUBLISH_ROUTES` (soft cap; no mid-feed eviction).
server.inject_relay_frame("live", "cam1", FrameType::Video, ts, &payload)?;
server.release_injected_route("live", "cam1");
// Or on shutdown / remesh: server.release_all_injected_routes();

// Late-joiner / remote-subscriber init snapshot from StreamCache.
if let Some(snap) = server.stream_init_snapshot("live", "cam1") {
    let _: &StreamInitSnapshot = &snap;
    let _ = snap.avc_header;
    let _ = EXTERNAL_RELAY_PUBLISHER_ID;
    let _ = is_external_publisher_id(EXTERNAL_RELAY_PUBLISHER_ID);
}

On an existing local publisher Conn, Conn::inject_relay_frame queues into pending_relay the same way as socket-received media.

HA / cluster mirroring notes

enable_relay_export + drain_exported_relay_frames mirror live relay frames only. Init state (AVC/AAC sequence headers, metadata, last keyframe) is not included in the export buffer.
Integrators mirroring to remote nodes must also call stream_init_snapshot (or equivalent init-cache handoff) so late joiners can decode the stream.
External inject routes (Server::inject_relay_frame) must call release_injected_route when a feed ends. Stale claims are reaped automatically after ~120s without frames, but explicit release is still recommended.

Conn::inject_relay_frame skips media auth callbacks.

Using via the `extern "C"` FFI

The crate also builds as a cdylib/staticlib and exposes a stable extern "C" API for use from C, Go, Python, PHP, and others. See src/lib.rs for the full FFI surface.

Server

lrtmp2_server_t *lrtmp2_server_create(const lrtmp2_server_config_t *config);
void             lrtmp2_server_destroy(lrtmp2_server_t *server);
int              lrtmp2_server_listen(lrtmp2_server_t *server, const char *bind_addr);
int              lrtmp2_server_poll(lrtmp2_server_t *server, int timeout_ms);
void             lrtmp2_server_stop(lrtmp2_server_t *server);

Client

lrtmp2_client_t *lrtmp2_client_create(const lrtmp2_server_config_t *config);
void             lrtmp2_client_destroy(lrtmp2_client_t *client);
int              lrtmp2_client_connect(lrtmp2_client_t *client, const char *url);
int              lrtmp2_client_publish(lrtmp2_client_t *client);
int              lrtmp2_client_play(lrtmp2_client_t *client);
int              lrtmp2_client_send_frame(lrtmp2_client_t *client, const lrtmp2_frame_t *frame);
int              lrtmp2_client_poll(lrtmp2_client_t *client, int timeout_ms);

Utilities

int          lrtmp2_tls_supported(void);
const char  *lrtmp2_version_string(void);
int          lrtmp2_version_major(void);
int          lrtmp2_version_minor(void);
int          lrtmp2_version_patch(void);
const char  *lrtmp2_error_string(int code);

Repository Structure

librtmp2/
├── src/
│   ├── lib.rs              Rust API + extern "C" FFI layer
│   ├── alloc.rs            Custom allocator hook
│   ├── amf/                AMF0 + AMF3 encoding/decoding
│   ├── buffer.rs           Growable byte buffers
│   ├── bytes.rs            Big-endian byte helpers
│   ├── chunk/              Chunk reader/writer/state (per-csid)
│   ├── client/             Outbound client: connect → publish/play
│   ├── ertmp/              E-RTMP v1/v2 parsers (see Implementation status)
│   ├── flv/                FLV tag parsers (library; not used in live relay path)
│   ├── handshake.rs        C0/C1/C2 ↔ S0/S1/S2
│   ├── media/              Init-frame cache classification + ModEx helpers shared by session/server
│   ├── message/            Message reassembly, control, commands
│   ├── net.rs              Host:port parsing shared by server bind / client connect
│   ├── server/             Listening socket, accept loop, relay
│   ├── session/            Connection state, publish/play handling
│   ├── transport.rs        TLS/plaintext transport
│   └── types.rs            Shared types
├── tests/
│   ├── interop/
│   └── server_client_loopback.rs
├── build.rs
├── Cargo.toml
└── docs/

Implementation status

Status reflects what is wired into the live session path (conn.rs, server/mod.rs, client/mod.rs), not merely what exists as parser code elsewhere in the repo.

Legacy RTMP — live path

Area	Status
Standard handshake (C0–C2)	Done
Encrypted / Adobe-digest handshake	Not implemented
Chunking, control messages, ping	Done
Commands `connect`, `createStream`, `publish`, `play`	Done
Commands `pause`, `seek`, `receiveAudio`, `receiveVideo`, `closeStream`	Done — `pause`/`receiveAudio`/`receiveVideo` gate per-frame relay; `closeStream` mirrors `deleteStream` cleanup
`FCPublish` / `releaseStream`	`FCPublish` ignored (no-op); `releaseStream` force-releases a stale publish-route claim so a reconnecting encoder can immediately republish
`FCUnpublish` / `deleteStream`	Done — clears publish route, play state (`is_playing`/`paused`), and sends `StreamEOF`
Audio / video ingest and relay	Done
Aggregate messages	Done (unpack → relay)
Publisher `onMetaData` parsing (stats)	Done — relayed live to players and cached for late joiners
AMF3 shared objects	Done — envelope (name/version/flags + event list) parsed and delivered via `on_shared_object_cb`; `Conn::send_shared_object` writes them. Event payloads are opaque bytes — interpreting `Change`/`SendMessage` contents as AMF is left to the host, per this crate's "deliver the event, not the policy" design
User Control `StreamBegin` / `StreamEOF` / `SetBufferLength`	Done — `StreamBegin`/`SetBufferLength` sent on `play`, `StreamEOF` sent on `deleteStream`/`closeStream`, inbound `SetBufferLength` read and stored
One stream per connection (`current_stream`)	By design today
Init-frame cache for late joiners	Legacy H.264 (`0x17`) + AAC, plus enhanced (ex-header) and multitrack sequence starts per track

E-RTMP v1

Area	Status
Enhanced A/V passthrough (HEVC/AV1/Opus from FFmpeg/OBS)	Done (opaque byte relay)
`exvideo_parse` / `exaudio_parse` in session hot path	Done — called for codec detection and init-cache classification
`fourCcList` in `connect`	Done — parsed on read; echoed back in the `_result` when v2 caps negotiation triggers
HDR / `colorInfo` (`metadata.rs`)	Done — an enhanced video Metadata packet (`ERTMP_PACKET_TYPE_METADATA`) is parsed and exposed via `Conn::detected_hdr_info` (Rust-only; kept off `Frame` to preserve its ABI-stable `#[repr(C)]` layout, see `docs/abi-policy.md`)
Enhanced sequence-start cache for players	Done (see init-frame cache above)
`exvideo_write` / `exaudio_write` helpers	Done — mirror `exvideo_parse` / `exaudio_parse` in reverse (`src/ertmp/exvideo.rs`, `src/ertmp/exaudio.rs`); `exvideo_write` covers enhanced (ex-header) headers only — `VideoHeader` carries no legacy codec ID, so legacy output is rejected (returns 0) rather than emitting an invalid tag byte

E-RTMP v2

Area	Status
`capsEx`, `videoFourCcInfoMap`, `reconnect`, `multitrack`, `modex` parse/write	Library code + unit tests, also wired into the session (see below)
v2 capability negotiation in session	Done — `negotiate_caps()` runs on `connect` when the client advertises v2 caps; state transitions to `CAPS_NEGOTIATED` and the response echoes negotiated caps
Multitrack / ModEx in session	Done — ModEx normalized on every ingested frame; multitrack containers demuxed per track for codec authorization and per-track init-cache headers
Reconnect in session	Done — `Conn::send_reconnect_request` / `Server::request_reconnect` send `NetConnection.Connect.ReconnectRequest`; the client detects it mid-session and fires `on_reconnect_request_cb` with the (optional) `tcUrl`. The client also advertises the `capsEx` reconnect bit + a `reconnect` value on `connect` whenever `on_reconnect_request_cb` is set, so spec-compliant servers know to expect it. The library only delivers the event — establishing the new connection is left to the host application

Client, TLS, tests

Area	Status
Minimal publish client	Done
Minimal play client (A/V receive callback)	Done — also delivers metadata (AMF0/AMF3 data) and handles Aggregate messages
RTMPS	Done
Loopback + FFmpeg interop tests	Present (`tests/`, `tests/interop/`)

Parser-level details and spec mappings: docs/protocol-mapping-legacy.md, docs/protocol-mapping-ertmp-v1.md, docs/protocol-mapping-ertmp-v2.md.

License

MIT — see LICENSE

Name		Name	Last commit message	Last commit date
Latest commit History 653 Commits
.cursor		.cursor
.github		.github
benches		benches
debian		debian
docs		docs
examples		examples
fuzz		fuzz
include/librtmp2		include/librtmp2
scripts		scripts
src		src
tests		tests
.gitignore		.gitignore
AGENTS.md		AGENTS.md
CHANGELOG.md		CHANGELOG.md
CLAUDE.md		CLAUDE.md
CONTRIBUTING.md		CONTRIBUTING.md
Cargo.toml		Cargo.toml
LICENSE		LICENSE
README.md		README.md
build.rs		build.rs
cbindgen.toml		cbindgen.toml
renovate.json		renovate.json

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librtmp2

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librtmp2

Overview

Architecture

State Machine

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TLS / RTMPS

Using as a Rust Crate

External media export / inject (Rust)

HA / cluster mirroring notes

Using via the extern "C" FFI

Server

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Utilities

Repository Structure

Implementation status

Legacy RTMP — live path

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