Introduction

Secure Reliable Transport (SRT) is an open source transport technology that optimizes streaming performance across unpredictable networks, such as the Internet.

Secure	Encrypts video streams
Reliable	Recovers from severe packet loss
Transport	Dynamically adapts to changing network conditions

SRT is applied to contribution and distribution endpoints as part of a video stream workflow to deliver the best quality and lowest latency video at all times.

As audio/video packets are streamed from a source to a destination device, SRT detects and adapts to the real-time network conditions between the two endpoints. SRT helps compensate for jitter and bandwidth fluctuations due to congestion over noisy networks, such as the Internet. Its error recovery mechanism minimizes the packet loss typical of Internet connections. And SRT supports AES encryption for end-to-end security, keeping your streams safe from prying eyes.

Join the conversation in the #development channel on Slack.

Guides

• Why SRT Was Created
• SRT Protocol Technical Overview
• Using the srt-live-transmit App
• SRT Encryption
• API
• Reporting problems

Requirements

• cmake (as build system)
• Tcl 8.5 (optional for user-friendly build system)
• OpenSSL
• Pthreads (for POSIX systems it's builtin, for Windows there's a library)

For detailed description of the build system and options, please read BuildOptions.md.

For Linux:

Install cmake and openssl-devel (or similar name) package. For pthreads there should be -lpthreads linker flag added.

Default installation path prefix of make install is /usr/local.

To define a different installation path prefix, use the --prefix option with configure or -DCMAKE_INSTALL_PREFIX CMake option.

To uninstall, call make -n install to list all the dependencies, and then pass the list to rm.

Ubuntu 14

sudo apt-get update
sudo apt-get upgrade
sudo apt-get install tclsh pkg-config cmake libssl-dev build-essential
./configure
make

CentOS 7

sudo yum update
sudo yum install tcl pkgconfig openssl-devel cmake gcc gcc-c++ make automake
./configure
make

CentOS 6

sudo yum update
sudo yum install tcl pkgconfig openssl-devel cmake gcc gcc-c++ make automake
sudo yum install centos-release-scl-rh devtoolset-3-gcc devtoolset-3-gcc-c++
scl enable devtoolset-3 bash
./configure --use-static-libstdc++ --with-compiler-prefix=/opt/rh/devtoolset-3/root/usr/bin/
make

For Mac (Darwin, iOS):

Homebrew supports "srt" formula.

brew update
brew install srt

If you prefer using a head commit of master branch, you should add --HEAD option to brew command.

brew install --HEAD srt

Also, SRT can be built with cmake and make on Mac. Install cmake and openssl with development files from "brew". Note that the system version of OpenSSL is inappropriate, although you should be able to use any newer version compiled from sources, if you prefer.

brew install cmake
brew install openssl
export OPENSSL_ROOT_DIR=$(brew --prefix openssl)
export OPENSSL_LIB_DIR=$(brew --prefix openssl)"/lib"
export OPENSSL_INCLUDE_DIR=$(brew --prefix openssl)"/include"
./configure
make

For Windows:

1. Prepare one of the following Windows crypto libraries:

(a) OpenSSL
(b) LibreSSL
(c) MbedTLS

(a) Using the OpenSSL binaries:

Download and install OpenSSL for Windows. The 64-bit developer package can be downloaded from here:

http://slproweb.com/download/Win64OpenSSL-1_0_2r.exe

Note that the last letter or version number may be changed, and older versions may no longer be available. If you can't find this version, check here:

http://slproweb.com/products/Win32OpenSSL.html

It's expected to be installed in C:\OpenSSL-Win64 (see the above variables). Note that this version is most likely compiled for Visual Studio 2013. For other versions, download and compile the sources from:

https://github.com/openssl/openssl

The instructions for compiling on Windows can be found here:

https://wiki.openssl.org/index.php/Compilation_and_Installation#Windows

Note that ActivePerl and nasm are required.

(b) Using the LibreSSL binaries:

Since LibreSSL has header files that are compatible with OpenSSL, cmake can use it like OpenSSL with little configuration.

The source code and binaries can be downloaded from here:

https://ftp.openbsd.org/pub/OpenBSD/LibreSSL/

Since there have been no new Windows builds since 2.6.0, you must build a new version yourself. LibreSSL comes with cmake build system support. Use the CMAKE_INSTALL_PREFIX variable to specify the directory that will contain the LibreSSL headers and libraries.

(c) Using the MbedTLS libraries:

MbedTLS source code can be downloaded from here:

https://tls.mbed.org/download

MbedTLS comes with cmake build system support. Use the CMAKE_INSTALL_PREFIX variable to specify the directory that will contain the MbedTLS headers and libraries. Note that building MbedTLS as a DLL is broken in version 2.16.3. You have to link it statically.

2. Compile and install Pthreads for Windows:

Compile and install pthread-win32 for Windows from GitHub: link.

1. Using Visual Studio 2013, open the project file pthread_lib.2013.vcxproj
2. Select configuration: Release and x64.
3. Make sure that the pthread_lib project will be built.
4. After building, find the pthread_lib.lib file (directory is usually bin\x64_MSVC2013.Release). Copy this file to C:\pthread-win32\lib (or whatever other location you configured in variables).
5. Copy include files to C:\pthread-win32\include (pthread.h, sched.h, and semaphore.h are in the toplevel directory. There are no meaningful subdirs here). Note that win## is part of the project name. It will become win32 or win64 depending on the selection.

3. Install cmake for Windows.

The cmake GUI will help you configure the project.

If you use MbedTLS, change the USE_ENCLIB to mbedtls.

It will try to find crypto library and pthreads. If you installed them in the default location, they will be found automatically. If not, you can define the following variables to help cmake find them:

For All:

CMAKE_PREFIX_PATH=<path to depended libraries root>

Note that CMAKE_PREFIX_PATH may be not shown in the cmake GUI. You can use Add Entry button to add the variable manually. Type is PATH. The directory structure should be similar to the following:

${CMAKE_PREFIX_PATH}/include/pthread.h
${CMAKE_PREFIX_PATH}/include/mbedtls/... (if mbedtls is used)
${CMAKE_PREFIX_PATH}/include/openssl/... (if openssl or libressl is not in default location)
${CMAKE_PREFIX_PATH}/lib/pthreadVC2.lib
${CMAKE_PREFIX_PATH}/lib/crypto.lib (if openssl or libressl is not in default location)
${CMAKE_PREFIX_PATH}/lib/mbedcrypto.lib (if mbedtls is used)

It's better to add the entry before clicking Configure, or the installation in system will be used instead of the one in ${CMAKE_PREFIX_PATH}.

For OpenSSL or LibreSSL:

OPENSSL_ROOT_DIR=<path to OpenSSL installation>
OPENSSL_LIBRARIES=<path to all the openssl libraries to link>
OPENSSL_INCLUDE_DIR=<path to the OpenSSL include dir>

For MbedTLS:

MBEDTLS_PREFIX=<path to mbedtls installation, default is the same to CMAKE_PREFIX_PATH>

For pthread:

PTHREAD_INCLUDE_DIR=<path to where pthread.h lies>
PTHREAD_LIBRARY=<path to pthread.lib>

Note that if you use the cmake command line to have it configured, please use / instead of \ in the path, or error messages may result.

4. For the sake of cmake generation: When you want to have a 64-bit version, remember that cmake by some reason adds /machine:X86 to the linker options. There are about four variables ended with _LINKER_FLAGS in the CMakeCache.txt file (also available with Advanced checked in CMake GUI). Remove them, or change into /machine:X64.

Also, just after you generated the project for MSVC (if you fail or forget to do that before the first compiling, you'll have to delete and regenerate all project files) then open Configuration Manager exactly after generation from cmake and setup x86 platform with requesting to generate this for every subproject.

5. IMPORTANT FOR DEVELOPERS AND CONTRIBUTORS: If you make any changes that fix something in the Windows version, remember to keep the project working also for all other platforms. To simplify the verification if you just would like to do it on the Windows machine, please install Cygwin and make another build for Cygwin, for example (remember that 'configure' script requires tcl8.5 package):

    mkdir build-cygwin
    cd build-cygwin
    ../configure --prefix=install --cygwin-use-posix
    make
   

The Cygwin platform isn't any important target platform for this project, but it's very useful to check if the project wouldn't be build-broken on Linux.