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CompilationGuide

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Generic


Version 5 (modified by saste, 4 years ago) (diff)

add "Post-installation troubleshoot" section

This page provides some generic instructions for compiling a project starting from the source code package under UNIX and derivatives. Note that the basic principles are shared by most Linux/Unix? distributions and MinGW.

Note that in this guide there is nothing strictly specific to FFmpeg.

Overview

Most source packages installation assumes the following steps:

  • configuration (through a configure script)
  • compilation (through make)
  • installation (through make install)

Configuration will allow to create the necessary files required by the following compilation step, and is done through a configure script usually provided by the source package. During configuration it is possible to define the install prefix and the enabled components.

Compilation usually consists into running make after the configuration step was done. In this phase the required libraries and binaries are generated.

Installation will install binaries and libraries in the path specified during the configuration step. Note that this step is not really required, since you can use the binaries compiled in the compilation path.

For a vanilla compilation and install, you will usually run the following commands:

configure
make
make install

This will compile the project files in the source directory, and will install the libraries in /usr/local. The third step may require super-user rights (so it may need to be replaced by sudo make install), since /usr/local cannot be modified by regular users.

Install path

A package consists of several related files which are installed in several directories. The configure step usually allows the user to specify the so-called install prefix, and is usually specified through the configure option configure --prefix=PREFIX, where PREFIX usually is by default /usr/local. The prefix specifies the common directory where all the components are installed.

The following directory are usually involved by the installation:

  • PREFIX/bin: contains the generated binaries (e.g. ffmpeg, ffplay, ffprobe etc. in the case of FFmpeg)
  • PREFIX/include: contains the library headers (e.g. libavutil/avstring.h, libavcodec/avcodec.h, libavformat/avformat.h etc. in case of FFmpeg), required to compile applications linked against the package libraries
  • PREFIX/lib: contains the generated libraris (e.g. libavutil, libavcodec, libavformat etc. in the case of FFmpeg)
  • PREFIX/share: contains various system-independent components, especially documentation files and examples

By specifying the prefix, it is possible to define the installation layout.

Using a shared prefix like /usr/local/, different packages will be installed in the same directory, so in general it will be more difficult to revert the installation.

Using a prefix like /opt/PROJECT/, the project will be installed in a dedicated directory, and to remove from the system you can simply remove the /opt/PREFIX path. On the other hand, such installation will require to edit all the environment variables to point to the custom path.

Environment variables

Several variables defined in the environment affect your package install. In particular, depending on your installation prefix, you may need to update some of these variables in order to make sure that the installed components can be found by the system tools.

The list of environment variables can be shown through the command env.

A list of the affected variables follows:

  • PATH: defines the list of :-separated paths where the system looks for binaries. For example if you install your package in /usr/local/, you should update the PATH so that it will contain /usr/local/bin. This can be done for example through the command export PATH=/usr/local/bin:$PATH.
  • LD_LIBRARY_PATH: contains the :-separated paths where the system looks for libraries. For example if you install your package in /usr/local/, you should update the LD_LIBRARY_PATH so that it will contain /usr/local/lib. This can be done for example through the command export LD_LIBRARY_PATH=/usr/local/lib:$LD_LIBRARY_PATH. This variable is sometimes deprecated in favor of the use of ldconfig.
  • CFLAGS
  • LDFLAGS
  • PKG_CONFIG_PATH

In case you installed a package in a non standard path, you need to update these environment libraries so that system tools will be able to detect the package components. This is especially required when running a configure script for a package relying on other installed libraries/headers/tools.

Environment variables are usually defined in the profile file, for example .profile defined in the user directory for sh/bash users, and in /etc/profile. You should probably update this file in order to set permanently your custom environment. Alternatively you can set the variables in a script or in a particular shell session.

Remember to export the variables to the child process, e.g. using the export command. Read the fine documentation of your shell for more detailed information.

LD_LIBRARY_PATH and ldconfig

When you link a library depending on other libraries, the tools will look for the libraries to link in a list of standard paths (typically, /usr/lib, and in other paths which are set in the system. Some systems rely on the LD_LIBRARY_PATH library. Alternatively you may set the global path through the ldconfig utility, which is done editing the /etc/ld.so.conf system configuration file.

Note that on some systems the LD_LIBRARY_PATH variable defined in the shell profile is reset for security reasons (e.g. see https://bugs.launchpad.net/ubuntu/+source/xorg/+bug/366728), so you may need to reset it per-session or per-script.

Configuration prerequisites and distribution packages

When configuring a package, you may be required to check for the presence of some required libraries and headers. Many distribution will provide binary package for the required libraries, so you may rely on that rather than compile and install from scratch.

In general, for a library you will need the library package and the development package associated to that library. The library package contains only the library, the development package will contain also the headers and the other files which are required for compiling a package depending on those libraries. On Debian-based distribution systems, the development packages have the -dev suffix, on RedHat?-based distribution systems, they have the -devel suffix.

For example on Debian, if you want to configure FFmpeg with --enable-libmp3lame, you will need to install the libmp3lame development package which will be called libmp3lame-dev.

You should also make sure that the library version provided by the distribution is compatible with the one required by the configured source package. If the required package is more recent than the library version provided by your distribution, you may need to install from source.

Post-installation troubleshoot

First of all verify that the binaries, headers and libraries have been installed in the supposed location (along the PREFIX path). To verify the binaries install you can simply run a command with the tool name, and verify the complete path with which -a, which will show all the tools with the given name available in the system.

Extra care must be paid in case you have several installations of the same package, in order to avoid conflicts.