This directory contains scripts to build a binary installer for libsrt on Windows systems for Visual Studio applications using SRT.

These initial steps need to be executed once only.

• Prerequisite 1: Install Visual Studio. The free Community Edition is recommended for open-source software. See https://visualstudio.microsoft.com/. Be sure to install the compilation tools for the all target architectures, including 64-bit Arm. In the Visual Studio Installer program, select "Modify" -> "Individual Components". In section "Compilers, build tools, and runtimes", select "MSVC v143 - VS2022 C++ ARM64/ARM64EC build tools (latest)" (the exact version may vary).

• Prerequisite 2: Install OpenSSL for Windows, 64-bit Intel, 32-bit Intel, 64-bit Arm. This can be done automatically by running the PowerShell script install-openssl.ps1. If you are interested in more information about OpenSSL for Windows, scroll to the appendix at the end of this page.

• Prerequisite 3: Install NSIS, the NullSoft Installation Scripting system. This can be done automatically by running the PowerShell script install-nsis.ps1.

To build the libsrt installer, simply run the PowerShell script build-win-installer.ps1. Running it without parameters, for instance launching it from the Windows Explorer, is sufficient to build the installer.

Optional parameters:

• -Version name : Use the specified string as version number for libsrt. By default, if the current commit has a tag, use that tag (initial "v" removed, for instance 1.4.3). Otherwise, the default version is a detailed version number (most recent version, number of commits since then, short commit SHA, for instance 1.4.3-32-g22cc924). Use that option if necessary to specify some other non-standard form of version string.

• -NoPause : Do not wait for the user to press <enter> at end of execution. By default, execute a pause instruction at the end of execution, which is useful when the script was launched from Windows Explorer. Use that option when the script is invoked from another PowerShell script.

The installer is then available in the directory installers.

The name of the installer is libsrt-VERS.exe where VERS is the SRT version number (see the -Version option).

The installer shall then be published as a release asset in the srt repository on GitHub, either as libsrt-VERS.exe or libsrt-VERS-win-installer.zip. In the latter case, the archive shall contain libsrt-VERS.exe.

To install the SRT libraries, simply run the libsrt-VERS.exe installer which is available in the SRT release area.

After installing the libsrt binaries, an environment variable named LIBSRT is defined with the installation root (typically C:\Program Files (x86)\libsrt).

If there is a need for automation, in a CI/CD pipeline for instance, the download of the latest libsrt-VERS.exe and its installation can be automated using the sample PowerShell script install-libsrt.ps1 which is available in this directory. This script may be freely copied in the user's build environment.

When run without parameters (for instance from the Windows explorer), this script downloads and installs the latest version of libsrt.

Optional parameters:

• -Destination path : Specify a local directory where the libsrt package will be downloaded. By default, use the tmp subdirectory from this script's directory.

• -ForceDownload : Force a download even if the package is already downloaded in the destination path. Note that the latest version is always checked. If a older package is already present but a newer one is available online, the newer one is always downloaded, even without this option.

• -GitHubActions : When used in a GitHub Actions workflow, make sure that the LIBSRT environment variable is propagated to subsequent jobs. In your GitHub workflow, in the initial setup phase, use script-dir\install-libsrt.ps1 -GitHubActions -NoPause.

• -NoInstall : Do not install the package, only download it. By default, libsrt is installed.

• -NoPause : Do not wait for the user to press <enter> at end of execution. By default, execute a pause instruction at the end of execution, which is useful when the script was launched from Windows Explorer. Use that option when the script is invoked from another PowerShell script.

In the SRT installation root directory (specified in environment variable LIBSRT), there is a Visual Studio property file named libsrt.props. Simply reference this property file in your Visual Studio project to use libsrt.

You can also do that manually by editing the application project file (the XML file named with a .vcxproj extension). Add the following line just before the end of the file:

<Import Project="$(LIBSRT)\libsrt.props"/>

With this setup, just compile your application normally, either using the Visual Studio IDE or the MSBuild command line tool.

This directory contains the following files:

The SRT protocol uses encryption. Internally, libsrt can use multiple cryptographic libraries but OpenSSL is the default choice on all platforms, including Windows.

OpenSSL is not part of the base installation of a Windows platform and should be separately installed. OpenSSL is neither "Windows-friendly" and the OpenSSL team does not provide Windows binaries.

The production of OpenSSL binaries for Windows is delegated to Shining Light Productions (http://slproweb.com/). Binaries for all architectures are available here: http://slproweb.com/products/Win32OpenSSL.html

This is automatically done by the PowerShell script install-openssl.ps1 in this directory. Let's see what's behind the scene.

First, the script determines which installers should be downloaded and where to get them from.

Initially, the HTML for the slproweb page was built on server-side. Our script grabbed the URL content, parsed the HTML and extracted the URL of the binaries for the latest OpenSSL packages from the "href" of the links.

At some point in 2024, the site changed policy. The Web page was no longer built on server-side, but on client-side. The downloaded HTML contains some JavaScript which dynamically builds the URL of the binaries for the latest OpenSSL binaries. The previous method now finds no valid package URL from the downloaded page (a full browser is needed to execute the JavaScript). The JavaScript downloads a JSON file which contains all references to the OpenSSL binaries.

Therefore, the script install-openssl.ps1 now uses the same method: download that JSON file and parse it.

The libsrt installer contains static libraries for all three architectures which are supported by Windows: x86, x64, Arm64. The corresponding static libraries for OpenSSL are also needed and included in the installer.

Because Visual Studio can build libraries and executables for all three architectures, on any build system, we need to install the OpenSSL headers and libraries for all three architectures, on the build system.

This is what the script install-openssl.ps1 does. However, the way to do this has changed over time.

As a starting point, there are three installers, one per architecture. All installers are x86 executables which can be run on any Windows system (Arm64 Windows emulates x86 and x64 when necessary). Additionally, the three sets of files are installed side by side, without overlap.

• x86: C:\Program Files (x86)\OpenSSL-Win32
• x64: C:\Program Files\OpenSSL-Win64
• Arm64: C:\Program Files\OpenSSL-Win64-ARM

So, the script install-openssl.ps1 installed them all and libsrt could be built for all architecture.

However, it works only on Arm64 systems. On x86 and x64 system, the OpenSSL installer for Arm64 fails. The installer executable can run but there is an explicit check in the installation process to abort when running on Intel systems.

Since most Windows build servers are Intel systems, this approach was no longer appropriate.

At some point, the producers of the OpenSSL binaries acknowledged the problem and they created an additional form of installer: the "universal" one. This package can be installed on any system and the binaries and headers are installed for all architectures, in one single location.

• Universal: C:\Program Files (x86)\OpenSSL-WinUniversal