BuildOptions.md

Build System

The main build system for SRT is provided by the cmake tool, which can be used directly. There's also a wrapper script named configure (requires Tcl interpreter) that can make operating with the options easier.

Portability

The cmake build system was tested on the following platforms:

• Linux (various flavors)
• macOS (see this separate document)
• Windows with MinGW
• Windows with Microsoft Visual Studio (see this separate document)
• Android (see this separate document)
• Cygwin (only for testing)

The configure script wasn't tested on Windows (other than on Cygwin).

The configure Script

This script is similar in design to the Autotools' configure script, and so usually handles --long-options, possibly with values. It handles two kinds of options:

• special options to be resolved inside the script and that may do some advanced checks; this should later turn into a set of specific cmake variable declarations

• options that are directly translated to cmake variables.

The direct translate option always does a simple transformation:

• all letters uppercase
• dash into underscore
• plus into X
• when no value is supplied, it defaults to 1

For example, --enable-c++11 turns into -DENABLE_CXX11=1 when passed to cmake.

Additionally, if you specify --disable-<X>, the configure script will automatically turn it into an associated --enable-<X> option, passing 0 as its value. For example, --disable-encryption will be translated for cmake into -DENABLE_ENCRYPTION=0.

Build Options

All options below are presented using the configure convention. They can all be used in cmake with the appropriate format changes.

--cygwin-use-posix (default:OFF)

When ON, compile on Cygwin using POSIX API (otherwise it will use MinGW environment).

--enable-apps (default: ON)

Enables compiling user applications.

--enable-code-coverage (default: OFF)

Enable instrumentation for code coverage. Note that this is only available on platforms with GNU-compatible compiler.

--enable-c++-deps (default: OFF)

The pkg-confg file (srt.pc) will be generated with the libstdc++ library as a dependency. This may be required in some cases where you have an application written in C which therefore won't link against libstdc++ by default.

--enable-c++11 (default: ON)

Enable compiling in C++11 mode for those parts that may require it. Parts that don't require it will still be compiled in C++03 mode, although which parts are affected may change in future.

If this option is turned OFF, it affects building a project in two ways:

• an alternative C++03 implementation can be used, if available
• otherwise the component that requires it will be disabled

Parts that currently require C++11 and have no alternative implementation are:

• unit tests
• user and testing applications (such as srt-live-transmit)
• some of the example applications

It should be possible to compile the SRT library without C++11 support. However, this alternative C++03 implementation may be unsupported on certain platforms.

--enable-debug=<0,1,2>

This option allows control through the CMAKE_BUILD_TYPE variable:

• 0 (default): Release (highly optimized, no debug info)
• 1: Debug (not optimized, full debug info)
• 2: RelWithDebInfo (highly optimized, but with debug info)

Please note that when the value is other than 0, the --enable-heavy-logging option is also turned ON by default.

--enable-encryption (default: ON)

Encryption feature enabled, which involves dependency on an external encryption library (default: openssl). If you disable encryption, the library will be unable to set encryption options. It will be compatible with a peer that has encryption enabled, but just won't use encryption for the connection.

--enable-getnameinfo (default: OFF)

Enables the use of getnameinfo using options that allow using reverse DNS to resolve an internal IP address into a readable internet domain name, so that it can be shown nicely in the log file. This option is turned OFF by default because it may have an impact on general performance. It is recommended only for development when testing on a local network.

--enable-haicrypt-logging (default: OFF)

Enables logging in the haicrypt module, which serves as a connector to an encryption library. Logging here might be seen as unsafe, therefore this option is turned OFF by default.

--enable-heavy-logging (default: OFF in release mode)

This option enables the logging instructions in the code, which are considered heavy as they occur often and cover many detailed aspects of library behavior. Turning this option ON will allow you to use the debug level of logging and get detailed information as to what happens inside the library. Note, however, that this may influence processing by changing times, using less preferred thread switching layouts, and generally worsen the functionality and performance of the library. For these reasons this option is turned OFF by default.

--enable-inet-pton (default: ON)

Enables usage of inet_pton function by the applications, which should be used to resolve the network endpoint name into an IP address. This may be not availabe on some version of Windows, in which case you can turn this OFF. When this option is OFF, however, IP addresses cannot be resolved by name, as the inet_pton function gets a poor-man's simple replacement that can only resolve numeric IPv4 addresses.

--enable-logging (default: ON)

Enables logging. When you turn this option OFF, the library will not report any runtime information through the logging system, including errors. This option may be useful if you suspect the logging system of impairing performance.

--enable-monotonic-clock (default: OFF)

This option enforces the use of clock_gettime to get the current time, instead of gettimeofday. This function forces the use of a monotonic clock that is independent of the currently set time in the system. The condition variables (CV), for which the *_timedwait() functions are used with time specification based on the time obtained from clock_gettime must be appropriately configured. For now, this is only done for the GarbageCollector controlling CV, not every CV used in SRT. The consequence of enabling this option, however, may be portability issues resulting from the fact that clock_gettime function may be unavailable in some SDKs or that an extra -lrt option is sometimes required (this requirement will be autodetected).

The problem is based on the fact that POSIX functions that use timeout specification (all of *_timedwait) expect the absolute time value. A relative timeout value can be then only specified by adding it to the current time, which can be specified as either system or monotonic clock (as configured in the resources used in the operation). However the current time of the monotonic clock can only be obtained by the clock_gettime function.

NOTE: This is a temporary fix for Issue #729 where the library could get stuck if the system clock is modified during an SRT transmission. This option will be removed when the problem is fixed globally.

--enable-stdcxx-sync (default: OFF)

This option enables the standard C++ thread and chrono libraries (available since C++11) to be used by SRT instead of the pthreads.

--enable-profile (default: OFF)

Enables code instrumentation for profiling.

This is available only for GNU-compatible compilers.

--enable-relative-libpath (default: OFF)

Enables adding a relative path to a library. This allows applications to be linked against a shared SRT library by reaching out to a sibling ../lib directory, provided that the library and applications are installed in POSIX/GNU style directories. This might be useful when installing SRT and applications in a directory, in which the library subdirectory is not explicitly defined among the global library paths. Consider, for example, this application and its required library:

• /opt/srt/bin/srt-live-transmit
• /opt/srt/lib64/libsrt.so

By using the --enable-relative-libpath option, the srt-live-transmit application has a relative library path defined inside as ../lib64. A dynamic linker will find the required libsrt.so file by this path: ../lib64/libsrt.so. This way the dynamic linkage will work even if /opt/srt/lib64 path isn't added to the system paths in /etc/ld.so.conf or in the LD_LIBRARY_PATH environment variable.

This option is OFF by default because of reports that it may cause problems in case of default installation.

--enable-shared and --enable-static (default for both: ON)

Enables building SRT as a shared and/or static library, as required for your application. In practice, you would only disable one or the other (e.g. by --disable-shared). Note that you can't disable both at once.

--enable-testing (default: OFF)

Enables compiling of developer testing applications.

--enable-thread-check (default: OFF)

Enables #include <threadcheck.h>, which implements THREAD_* macros" to support better thread debugging. Included to support an existing project.

--enable-unittests (default: OFF)

When ON, this option enables unit tests, possibly with the download and installation of the Google test library in the build directory. The tests will be run as part of the build process. This is intended for developers only.

--openssl-crypto-library=<filepath>

Configure the path to an OpenSSL Crypto library.

--openssl-include-dir=<path>

Configure the path to include files for an OpenSSL library.

--openssl-ssl-library=<filepath>

Configure the path to an OpenSSL SSL library.

--pkg-config-executable=<filepath>

Configure the path to the pkg-config tool.

--prefix=<path>

This is an alias to the --cmake-install-prefix variable that establishes the root directory for installation, inside of which a GNU/POSIX compatible directory layout will be used. As on all known build systems, this defaults to /usr/local on GNU/POSIX compatible systems, with lower level GNU/POSIX directories created inside: /usr/local/bin,/usr/local/lib, etc.

--pthread-include-dir=<path>

Configure the path to include files for a pthread library. Note that this is useful only on Windows. On Linux and macOS this path should be available in the system.

--pthread-library=<filepath>

Configure the path to a pthread library.

--use-busy-waiting (default: OFF)

Enable more accurate sending times at the cost of potentially higher CPU load.

This option will cause more empty loop running, which may cause more CPU usage. Keep in mind, however, that when processing high bitrate streams the share of empty loop runs will decrease as the bitrate increases. This way higher CPU usage would still be productive, while without system-supported waiting this option may increase the likelihood of switching to the right thread at the time when it is expected to be revived.

--use-c++-std=<standard>

Enforce using particular C++ standard when compiling. When using this option remember that:

• Allowed values are: 98, 03, 11, 14, 17 and 20
• If you use 98/03 and --enable-apps, apps will be still using C++11
• This option is only supported on GNU and Clang compilers (will be ignored on others)

--use-gnustl

Use pkg-config with the gnustl package name to extract the header and library path for the C++ standard library (instead of using the compiler built-in one).

--use-enclib=<name>

Encryption library to be used. Possible options for <name>:

• openssl (default)
• gnutls (with nettle)
• mbedtls

--use-openssl-pc (default: ON)

Use pkg-config to find OpenSSL libraries. You can turn this OFF to force cmake to find OpenSSL by its own preferred method.

--use-static-libstdc++ (default: OFF)

Enforces linking the SRT library against the static libstdc++ library. This may be useful if you are using SRT library in an environment where it would by default link against the wrong version of the C++ standard library, or when the library in the version used by the compiler is not available as shared.

--with-compiler-prefix=<prefix>

Sets C/C++ toolchains as <prefix><c-compiler> and <prefix><c++-compiler>.

This option will override the default compiler autodetected by cmake. It is handled inside cmake. It sets the variables CMAKE_C_COMPILER and CMAKE_CXX_COMPILER. The values for the above <c-compiler> and <c++-compiler> are controlled by the --with-compiler-type option. When this option is not supplied, a system-default compiler will be used, that is:

• On Mac OS (Darwin): clang
• On other POSIX systems: gcc
• On other systems: obtained from CMAKE_C_COMPILER variable

Instead of --with-compiler-prefix you can use --cmake-c-compiler and --cmake-c++-compiler options. This can be thought of as a shortcut, useful when you have a long path to the compiler command.

NOTE: The prefix is meant to simply precede the compiler type as pure prefix, so if your prefix is a full path to the compiler, it must include the terminal path separator character, as this can be also used as a prefix for a platform-specific cross compiler. For example, if the path to the C compiler is: /opt/arm-tc/bin/arm-linux-gnu-gcc-7.4, then you should specify --with-compiler-prefix=/opt/arm-tc/bin/arm-linux-gnu- and --with-compiler-type=gcc-7.4.

--with-compiler-type=<name>

Sets the compiler type to be used as <c-compiler> and <c++-compiler> respectively:

• gcc (default): gcc and g++
• cc: cc and c++
• others: use <name> as C compiler and <name>++ as C++ compiler

This should be the exact command used as a C compiler, possibly with version suffix, e.g. clang-1.7.0. If this option is used together with --with-compiler-prefix, its prefix will be added in front.

--with-extralibs=<library-list>

This is an option required for unusual situations when a platform-specific workaround is needed and some extra libraries must be passed explicitly for linkage. The argument is a space-separated list of linker options or library names.

There are some known sitautions where it may be necessary:

1. Some older Linux systems do not ship clock_gettime functions by default in their libc, and need an extra librt. If you are using POSIX monotonic clocks (see --enable-monotonic-clock), this might be required to add -lrd through this option. Although this situation is tried to be autodetected and this option added automatically, it might sometimes fail.

2. On some systems (found so far on OpenSuSE), if you use C++11 sync (see --enable-stdc++-sync), the gcc compiler relies on gthreads, which relies on pthreads, and happens to define inline source functions in the header that refers to pthread_create, the compiler however doesn't link against pthreads by default. To work this around, add -pthreads using this option.