Robotweax SRT

Robotweax SRT is an independent implementation of Secure Reliable Transport (SRT). It provides the familiar public SRT C API, reliable low-latency UDP transport, encryption, rendezvous connections, File/Stream mode, packet filtering, and connection groups in a portable C++20 library.

The project favors explicit compatibility boundaries, bounded protocol state, and reproducible tests. It is suitable for developers who want to embed SRT, build transport tools, or evaluate an alternative implementation without depending on implementation-specific C++ internals.

Release status

Version 0.2.4 is a pre-1.0 maintenance release with documented qualification limits, including outstanding independent cryptographic review.

Axis	Robotweax SRT 0.2.4
Project release	0.2.4
Shared-library ABI	0.2
Default public API target	SRT 1.5.7
srt_getversion()	1.5.7
Supported handshake generation	HSv5
Default encryption	AES-CTR
Optional encryption extension	AES-GCM, explicit build-time opt-in

The project version, shared-library ABI, compatible API version, wire handshake, and encryption profile are separate version axes. In particular, srt_getversion() reports the compatible SRT API target, not the Robotweax release number.

Version 0.2 is a pre-1.0 release. Rebuild applications and dependencies when moving between ABI lines. See the 0.2.4 release notes and 0.1-to-0.2 migration guide.

Highlights

• IPv4 and IPv6 Caller/Listener and Rendezvous connections over HSv5;
• Message and Stream I/O through <srt/srt.h>;
• blocking, nonblocking, timeout, callback, and epoll-style operation;
• LiveCC and FileCC congestion control;
• AES-CTR with 128-, 192-, or 256-bit keys and runtime key rotation;
• released, opt-in AES-GCM extension with authenticated payloads;
• Row, Column, and Matrix packet-filter FEC;
• Broadcast and Backup connection groups for supported Live use cases;
• Stream ID, socket-option, statistics, logging, and file-helper APIs;
• static and shared libraries on Linux, macOS, and Windows;
• CMake package and pkg-config metadata for installed consumers.

Robotweax implements a substantial SRT 1.5.7-compatible surface, but it does not claim to be a universal drop-in replacement for every libsrt deployment. Unsupported features and combinations fail explicitly. Review known limitations before deployment.

The current reference profile is the immutable official Haivision SRT v1.5.7 tag at commit 899348d8318eb9a3c5a5b6ec43c4a1114288773a. Compatibility claims remain feature- and topology-specific; older 1.5.5 and 1.5.6 references are retained as focused backward/security lanes.

Quick start

Requirements:

• CMake 3.20 or newer;
• a C++20 compiler;
• OpenSSL 3.x development files;
• Python 3.10 or newer when building the test suite.

Configure, build, and test an out-of-source Release tree:

cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build --parallel
ctest --test-dir build --output-on-failure

For multi-config generators such as Visual Studio, omit CMAKE_BUILD_TYPE and select the configuration when building and testing:

cmake -S . -B build
cmake --build build --config Release --parallel
ctest --test-dir build -C Release --output-on-failure

The default static development build includes tests, protocol tools, and microbenchmarks. For a lean installable build:

cmake -S . -B build-install \
  -DCMAKE_BUILD_TYPE=Release \
  -DROBOTWEAX_SRT_BUILD_TESTS=OFF \
  -DROBOTWEAX_SRT_BUILD_BENCHMARKS=OFF \
  -DROBOTWEAX_SRT_BUILD_TOOLS=OFF
cmake --build build-install --parallel
cmake --install build-install --prefix "$PWD/stage"

See Building and installing for shared libraries, build options, platform notes, and troubleshooting.

Use from CMake

After installation, consume the exported package and stable public target:

find_package(RobotweaxSRT 0.2 CONFIG REQUIRED)

add_executable(my_srt_app main.cpp)
target_link_libraries(my_srt_app PRIVATE RobotweaxSRT::srt)

If Robotweax SRT is installed under a custom prefix, add that prefix to CMAKE_PREFIX_PATH. POSIX consumers may alternatively use:

pkg-config --cflags --libs robotweax-srt

The default library name is robotweax-srt (librobotweax-srt on Unix-like systems, robotweax-srt.dll for Windows shared builds). Headers live below include/robotweax-srt; package metadata supplies that include root, preserving #include <srt/srt.h>. See installation layouts for the optional legacy layout and migration guidance.

Public API

Prefer the installed compatibility header:

#include <srt/srt.h>

The flat <srt.h> include is also installed for source compatibility. Start the process runtime before creating sockets and release it after all sockets have closed:

if (srt_startup() == SRT_ERROR) {
    /* inspect srt_getlasterror_str() */
}

SRTSOCKET socket = srt_create_socket();
/* Configure, bind/connect, and transfer data. */

(void)srt_close(socket);
(void)srt_cleanup();

Configure connection-stage options before srt_bind, srt_listen, or srt_connect. Select Message or Stream semantics deliberately and use srt_sendmsg2/srt_recvmsg2 when message-control metadata is required.

Read the Integration guide, public API compatibility, and socket-option reference before porting an existing application.

For a continuous MPEG-TS UDP → SRT → UDP relay, start with the live UDP/SRT bridge demo.

For runnable public-API examples, build the opt-in srt_message_demo, srt_file_demo, and srt_group_demo, or copy the standalone installed-package consumer to validate a downstream CMake integration. The three networked demos demonstrate Caller, Listener, and Rendezvous operation; Message and Stream I/O; Stream ID; nonblocking epoll usage; srt_sendfile/srt_recvfile; Broadcast and weighted Backup groups with a controlled member failover; AES-CTR or opt-in AES-GCM; packet-filter configuration; and srt_bistats without depending on private implementation headers.

Encryption profiles

The default build provides compatible AES-CTR behavior. Configure SRTO_PASSPHRASE, SRTO_PBKEYLEN, and related rotation options before connection establishment.

Robotweax SRT 0.2.0 also releases an explicit AES-GCM extension. It is enabled with the historical build flag ENABLE_AEAD_API_PREVIEW:

cmake -S . -B build-gcm \
  -DCMAKE_BUILD_TYPE=Release \
  -DENABLE_AEAD_API_PREVIEW=ON
cmake --build build-gcm --parallel
ctest --test-dir build-gcm --output-on-failure

The flag name is retained for source and build compatibility; AES-GCM is a released, version-pinned Robotweax 0.2 extension. A GCM-enabled installed CMake target propagates the required compile definition to consumers. Do not mix headers or binaries from default and GCM-enabled builds.

See Encryption and key rotation for configuration, negotiation, payload budgets, and supported combinations.

Documentation

Start with the documentation index:

• Getting started
• Building and installing
• Integration guide
• FFmpeg integration
• GStreamer integration
• VLC integration
• OBS integration
• OBS Windows integration
• Testing
• Known limitations
• File/Stream mode
• Rendezvous
• Connection groups
• Packet-filter FEC
• Live timing
• Statistics
• Logging

Platform scope

The supported build matrix covers current Linux, macOS, and Windows toolchains. Network behavior is designed to be portable, but some native socket options are platform-specific. For example, interface binding is Linux-only and explicit IPv6 traffic-class setting is unavailable through Winsock. The library returns a defined unsupported-operation error rather than reporting a setting that was not applied.

Application owners remain responsible for topology, reconnection policy, credential handling, operating-system tuning, and production qualification on their own networks and workloads.

Contributing and security

Bug reports and focused changes are welcome. Please read CONTRIBUTING.md before opening a pull request. Report security issues through the process in SECURITY.md, not a public issue.

Third-party attributions are listed in THIRD_PARTY.md. Robotweax SRT is distributed under the terms in LICENSE.