librtmp2

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

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Overview

librtmp2 implements the lowest protocol layer of RTMP: handshake, chunking, AMF, commands, audio/video tags, Enhanced RTMP extensions, state machine, and a clean callback API.

It is designed to be embedded into custom servers, clients, relay tools, OBS/FFmpeg integrations, or any future product that needs a solid RTMP foundation.

What it is:

• A complete Legacy RTMP implementation (handshake, chunk streams, message reassembly, commands, control messages)
• E-RTMP v1 support: ExVideoTagHeader, FourCC codecs (hvc1, av01, vp09), HDR metadata
• E-RTMP v2 support: capability negotiation (capsEx, videoFourCcInfoMap), reconnect, multitrack, ModEx
• An idiomatic Rust API plus an extern "C" FFI layer for use from C, Go, Python, PHP, and others
• RTMPS (RTMP over TLS) via the optional tls Cargo feature (OpenSSL), enabled by default

What it is not:

• Not an HTTP server or web UI
• Not a media server with business logic
• Not a push-relay to third-party platforms
• Not an FFmpeg wrapper

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Architecture

OBS / FFmpeg / App
        │
        ▼
      librtmp2          ← this library
      ├── Handshake
      ├── Chunking
      ├── AMF (AMF0 / AMF3)
      ├── RTMP Commands
      ├── E-RTMP v1
      └── E-RTMP v2

The library processes bytes, frames, commands, and protocol states. What a host program does with them is decided entirely via callbacks and configuration structures.

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State Machine

TCP_ACCEPTED
  → HANDSHAKE
  → CONNECTED
  → CAPS_NEGOTIATED     (E-RTMP v2)
  → APP_CONNECTED
  → STREAM_CREATED
  → PUBLISHING | PLAYING
  → CLOSING
  → CLOSED

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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.

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Using as a Rust Crate

Add to your Cargo.toml:

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

Without TLS:

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

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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);

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Repository Structure

librtmp2/
├── src/
│   ├── lib.rs              Rust API + extern "C" FFI layer
│   ├── alloc.rs            Custom allocator hook
│   ├── amf.rs              AMF0 + AMF3 encoding/decoding
│   ├── buffer.rs           Growable byte buffers
│   ├── bytes.rs            Big-endian byte helpers
│   ├── chunk.rs            Chunk reader/writer/state (per-csid)
│   ├── client.rs           Outbound client: connect → publish/play
│   ├── ertmp.rs            E-RTMP v1/v2 extensions
│   ├── flv.rs              FLV audio/video/script tag parsing
│   ├── handshake.rs        C0/C1/C2 ↔ S0/S1/S2
│   ├── log.rs              Logging
│   ├── message.rs          Message reassembly, control, commands
│   ├── net.rs              Network helpers
│   ├── server.rs           Listening socket, accept loop, per-connection poll
│   ├── session.rs          Connection state machine, stream bookkeeping
│   ├── transport.rs        TLS/plaintext transport abstraction
│   └── types.rs            Shared types
├── tests/
│   ├── interop/
│   └── server_client_loopback.rs
├── build.rs
├── Cargo.toml
└── docs/

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Roadmap

Feature	Status
Legacy RTMP server — minimal	Implemented
Legacy RTMP client — minimal	Implemented
E-RTMP v1 receive (HEVC/AV1 detection)	Implemented
E-RTMP v1 send	Implemented
E-RTMP v2 capability layer	Implemented
Multitrack / reconnect / ModEx	Implemented
RTMPS (TLS)	Implemented
End-to-end test suites	In progress
Performance benchmarks	Planned

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License

MIT — see LICENSE