# Platform Specific information

# Table of Contents

# 1. Unix-like

Some parts of Libav cannot be built with version 2.15 of the GNU assembler which is still provided by a few AMD64 distributions. To make sure your compiler really uses the required version of gas after a binutils upgrade, run:

    $(gcc -print-prog-name=as) --version

If not, then you should install a different compiler that has no hard-coded path to gas. In the worst case pass `--disable-asm` to configure.

## 1.1 BSD

BSD make will not build Libav, you need to install and use GNU Make (‘`gmake`’).

## 1.2 (Open)Solaris

GNU Make is required to build Libav, so you have to invoke (‘`gmake`’), standard Solaris Make will not work. When building with a non-c99 front-end (gcc, generic suncc) add either `--extra-libs=/usr/lib/values-xpg6.o` or `--extra-libs=/usr/lib/64/values-xpg6.o` to the configure options since the libc is not c99-compliant by default. The probes performed by configure may raise an exception leading to the death of configure itself due to a bug in the system shell. Simply invoke a different shell such as bash directly to work around this:

    bash ./configure

## 1.3 Darwin (OS X, iPhone)

The toolchain provided with Xcode is sufficient to build the basic unacelerated code.

OS X on PowerPC or ARM (iPhone) requires a preprocessor from git://git.libav.org/gas-preprocessor.git to build the optimized assembler functions. Put the Perl script somewhere in your PATH, Libav’s configure will pick it up automatically.

OS X on AMD64 and x86 requires `yasm` to build most of the optimized assembler functions Homebrew, Gentoo Prefix or MacPorts can easily provide it.

# 2. DOS

Using a cross-compiler is preferred for various reasons. http://www.delorie.com/howto/djgpp/linux-x-djgpp.html

# 3. OS/2

For information about compiling Libav on OS/2 see http://www.edm2.com/index.php/FFmpeg.

# 4. Windows

## 4.1 Native Windows compilation

Libav can be built to run natively on Windows using the MinGW tools. Install the latest versions of MSYS and MinGW from http://www.mingw.org/. You can find detailed installation instructions in the download section and the FAQ.

Libav does not build out-of-the-box with the packages the automated MinGW installer provides. It also requires coreutils to be installed and many other packages updated to the latest version. The minimum version for some packages are listed below:

- bash 3.1
- msys-make 3.81-2 (note: not mingw32-make)
- w32api 3.13
- mingw-runtime 3.15

Libav automatically passes `-fno-common` to the compiler to work around a GCC bug (see http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37216).

Notes:

- Building natively using MSYS can be sped up by disabling implicit rules in the Makefile by calling `make -r` instead of plain `make`. This speed up is close to non-existent for normal one-off builds and is only noticeable when running make for a second time (for example in `make install`).
- In order to compile AVplay, you must have the MinGW development library of SDL. Edit the ‘`bin/sdl-config`’ script so that it points to the correct prefix where SDL was installed. Verify that ‘`sdl-config`’ can be launched from the MSYS command line.
- By using `./configure --enable-shared` when configuring Libav, you can build libavutil, libavcodec and libavformat as DLLs.

## 4.2 Microsoft Visual C++ compatibility

As stated in the FAQ, Libav will not compile under MSVC++. However, if you want to use the libav* libraries in your own applications, you can still compile those applications using MSVC++. But the libav* libraries you link to must be built with MinGW. However, you will not be able to debug inside the libav* libraries, since MSVC++ does not recognize the debug symbols generated by GCC. We strongly recommend you to move over from MSVC++ to MinGW tools.

This description of how to use the Libav libraries with MSVC++ is based on Microsoft Visual C++ 2005 Express Edition. If you have a different version, you might have to modify the procedures slightly.

### 4.2.1 Using static libraries

Assuming you have just built and installed Libav in ‘`/usr/local`’.

1. Create a new console application ("File / New / Project") and then select "Win32 Console Application". On the appropriate page of the Application Wizard, uncheck the "Precompiled headers" option.
2. Write the source code for your application, or, for testing, just copy the code from an existing sample application into the source file that MSVC++ has already created for you. For example, you can copy ‘`libavformat/output-example.c`’ from the Libav distribution.
3. Open the "Project / Properties" dialog box. In the "Configuration" combo box, select "All Configurations" so that the changes you make will affect both debug and release builds. In the tree view on the left hand side, select "C/C++ / General", then edit the "Additional Include Directories" setting to contain the path where the Libav includes were installed (i.e. ‘`c:\msys\1.0\local\include`’). Do not add MinGW’s include directory here, or the include files will conflict with MSVC’s.
4. Still in the "Project / Properties" dialog box, select "Linker / General" from the tree view and edit the "Additional Library Directories" setting to contain the ‘`lib`’ directory where Libav was installed (i.e. ‘`c:\msys\1.0\local\lib`’), the directory where MinGW libs are installed (i.e. ‘`c:\mingw\lib`’), and the directory where MinGW’s GCC libs are installed (i.e. ‘`C:\mingw\lib\gcc\mingw32\4.2.1-sjlj`’). Then select "Linker / Input" from the tree view, and add the files ‘`libavformat.a`’, ‘`libavcodec.a`’, ‘`libavutil.a`’, ‘`libmingwex.a`’, ‘`libgcc.a`’, and any other libraries you used (i.e. ‘`libz.a`’) to the end of "Additional Dependencies".
5. Now, select "C/C++ / Code Generation" from the tree view. Select "Debug" in the "Configuration" combo box. Make sure that "Runtime Library" is set to "Multi-threaded Debug DLL". Then, select "Release" in the "Configuration" combo box and make sure that "Runtime Library" is set to "Multi-threaded DLL".
6. Click "OK" to close the "Project / Properties" dialog box.
7. MSVC++ lacks some C99 header files that are fundamental for Libav. Get msinttypes from http://code.google.com/p/msinttypes/downloads/list and install it in MSVC++’s include directory (i.e. ‘`C:\Program Files\Microsoft Visual Studio 8\VC\include`’).
8. MSVC++ also does not understand the `inline` keyword used by Libav, so you must add this line before `#include`ing libav*:

       #define inline _inline

9. Build your application, everything should work.

### 4.2.2 Using shared libraries

This is how to create DLL and LIB files that are compatible with MSVC++:

Within the MSYS shell, build Libav with

    ./configure --enable-shared
    make
    make install

Your install path (‘`/usr/local/`’ by default) should now have the necessary DLL and LIB files under the ‘`bin`’ directory.

Alternatively, build the libraries with a cross compiler, according to the instructions below in Cross compilation for Windows with Linux.

To use those files with MSVC++, do the same as you would do with the static libraries, as described above. But in Step 4, you should only need to add the directory where the LIB files are installed (i.e. ‘`c:\msys\usr\local\bin`’). This is not a typo, the LIB files are installed in the ‘`bin`’ directory. And instead of adding the static libraries (‘`libxxx.a`’ files) you should add the MSVC import libraries (‘`avcodec.lib`’, ‘`avformat.lib`’, and ‘`avutil.lib`’). Note that you should not use the GCC import libraries (‘`libxxx.dll.a`’ files), as these will give you undefined reference errors. There should be no need for ‘`libmingwex.a`’, ‘`libgcc.a`’, and ‘`wsock32.lib`’, nor any other external library statically linked into the DLLs.

Libav headers do not declare global data for Windows DLLs through the usual dllexport/dllimport interface. Such data will be exported properly while building, but to use them in your MSVC++ code you will have to edit the appropriate headers and mark the data as dllimport. For example, in libavutil/pixdesc.h you should have:

    extern __declspec(dllimport) const AVPixFmtDescriptor av_pix_fmt_descriptors[];

Note that using import libraries created by dlltool requires the linker optimization option to be set to "References: Keep Unreferenced Data (`/OPT:NOREF`)", otherwise the resulting binaries will fail during runtime. This isn’t required when using import libraries generated by lib.exe. This issue is reported upstream at http://sourceware.org/bugzilla/show_bug.cgi?id=12633.

To create import libraries that work with the `/OPT:REF` option (which is enabled by default in Release mode), follow these steps:

1. Open ‘`Visual Studio 2005 Command Prompt`’.

   Alternatively, in a normal command line prompt, call ‘`vcvars32.bat`’ which sets up the environment variables for the Visual C++ tools (the standard location for this file is ‘`C:\Program Files\Microsoft Visual Studio 8\VC\bin\vcvars32.bat`’).

2. Enter the ‘`bin`’ directory where the created LIB and DLL files are stored.
3. Generate new import libraries with ‘`lib.exe`’:

       lib /machine:i386 /def:..\lib\avcodec-53.def  /out:avcodec.lib
       lib /machine:i386 /def:..\lib\avdevice-53.def /out:avdevice.lib
       lib /machine:i386 /def:..\lib\avfilter-2.def  /out:avfilter.lib
       lib /machine:i386 /def:..\lib\avformat-53.def /out:avformat.lib
       lib /machine:i386 /def:..\lib\avutil-51.def   /out:avutil.lib
       lib /machine:i386 /def:..\lib\swscale-2.def   /out:swscale.lib

## 4.3 Cross compilation for Windows with Linux

You must use the MinGW cross compilation tools available at http://www.mingw.org/.

Then configure Libav with the following options:

    ./configure --target-os=mingw32 --cross-prefix=i386-mingw32msvc-

(you can change the cross-prefix according to the prefix chosen for the MinGW tools).

Then you can easily test Libav with Wine.

## 4.4 Compilation under Cygwin

Please use Cygwin 1.7.x as the obsolete 1.5.x Cygwin versions lack llrint() in its C library.

Install your Cygwin with all the "Base" packages, plus the following "Devel" ones:

    binutils, gcc4-core, make, git, mingw-runtime, texi2html

And the following "Utils" one:

    diffutils

Then run

    ./configure

to make a static build.

The current `gcc4-core` package is buggy and needs this flag to build shared libraries:

    ./configure --enable-shared --disable-static --extra-cflags=-fno-reorder-functions

If you want to build Libav with additional libraries, download Cygwin "Devel" packages for Ogg and Vorbis from any Cygwin packages repository:

    libogg-devel, libvorbis-devel

These library packages are only available from Cygwin Ports:

    yasm, libSDL-devel, libdirac-devel, libfaac-devel, libgsm-devel,
    libmp3lame-devel, libschroedinger1.0-devel, speex-devel, libtheora-devel,
    libxvidcore-devel

The recommendation for libnut and x264 is to build them from source by yourself, as they evolve too quickly for Cygwin Ports to be up to date.

Cygwin 1.7.x has IPv6 support. You can add IPv6 to Cygwin 1.5.x by means of the `libgetaddrinfo-devel` package, available at Cygwin Ports.

## 4.5 Crosscompilation for Windows under Cygwin

With Cygwin you can create Windows binaries that do not need the cygwin1.dll.

Just install your Cygwin as explained before, plus these additional "Devel" packages:

    gcc-mingw-core, mingw-runtime, mingw-zlib

and add some special flags to your configure invocation.

For a static build run

    ./configure --target-os=mingw32 --extra-cflags=-mno-cygwin --extra-libs=-mno-cygwin

and for a build with shared libraries

    ./configure --target-os=mingw32 --enable-shared --disable-static --extra-cflags=-mno-cygwin --extra-libs=-mno-cygwin