general.texi

mediastreamer2是开源的网络传输媒体流的库

@code{X} means that encoding (resp. decoding) is supported.

@code{I} means that an integer-only version is available, too (ensures high
performance on systems without hardware floating point support).

@chapter Platform Specific information

@section BSD

BSD make will not build FFmpeg, you need to install and use GNU Make
(@file{gmake}).

@section Windows

To get help and instructions for building FFmpeg under Windows, check out
the FFmpeg Windows Help Forum at
@url{http://arrozcru.no-ip.org/ffmpeg/}.

@subsection Native Windows compilation

FFmpeg can be built to run natively on Windows using the MinGW tools. Install
the current versions of MSYS and MinGW from @url{http://www.mingw.org/}. Also
install the coreutils package. You can find detailed installation
instructions in the download section and the FAQ.

Within the MSYS shell, configure and make with:

@example
./configure --enable-memalign-hack
make
make install
@end example

This will install @file{ffmpeg.exe} along with many other development files
to @file{/usr/local}. You may specify another install path using the
@code{--prefix} option in @file{configure}.

Notes:

@itemize

@item Use at least bash 3.1. Older versions are known to fail on the
configure script.

@item In order to compile vhooks, you must have a POSIX-compliant libdl in
your MinGW system. Get dlfcn-win32 from
@url{http://code.google.com/p/dlfcn-win32}.

@item In order to compile FFplay, you must have the MinGW development library
of SDL. Get it from @url{http://www.libsdl.org}.
Edit the @file{bin/sdl-config} script so that it points to the correct prefix
where SDL was installed. Verify that @file{sdl-config} can be launched from
the MSYS command line.

@item The target @code{make wininstaller} can be used to create a
Nullsoft-based Windows installer for FFmpeg and FFplay. @file{SDL.dll}
must be copied to the FFmpeg directory in order to build the
installer.

@item By using @code{./configure --enable-shared} when configuring FFmpeg,
you can build libavutil, libavcodec and libavformat as DLLs.

@end itemize

@subsection Microsoft Visual C++ compatibility

As stated in the FAQ, FFmpeg 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 @emph{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 FFmpeg 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.

@subsubsection Using static libraries

Assuming you have just built and installed FFmpeg in @file{/usr/local}.

@enumerate

@item 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.

@item 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
@file{output_example.c} from the FFmpeg distribution.

@item 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 FFmpeg includes were
installed (i.e. @file{c:\msys\1.0\local\include}).

@item Still in the "Project / Properties" dialog box, select
"Linker / General" from the tree view and edit the
"Additional Library Directories" setting to contain the @file{lib}
directory where FFmpeg was installed (i.e. @file{c:\msys\1.0\local\lib}),
the directory where MinGW libs are installed (i.e. @file{c:\mingw\lib}),
and the directory where MinGW's GCC libs are installed
(i.e. @file{C:\mingw\lib\gcc\mingw32\4.2.1-sjlj}). Then select
"Linker / Input" from the tree view, and add the files @file{libavformat.a},
@file{libavcodec.a}, @file{libavutil.a}, @file{libmingwex.a},
@file{libgcc.a}, and any other libraries you used (i.e. @file{libz.a})
to the end of "Additional Dependencies".

@item 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".

@item Click "OK" to close the "Project / Properties" dialog box.

@item MSVC++ lacks some C99 header files that are fundamental for FFmpeg.
Get msinttypes from @url{http://code.google.com/p/msinttypes/downloads/list}
and install it in MSVC++'s include directory
(i.e. @file{C:\Program Files\Microsoft Visual Studio 8\VC\include}).

@item MSVC++ also does not understand the @code{inline} keyword used by
FFmpeg, so you must add this line before @code{#include}ing libav*:
@example
#define inline _inline
@end example

@item If you used @file{output_example.c} as your sample application,
you will have to edit the @code{#include}s to point to the files which
are under the @file{ffmpeg} directory (i.e. @code{<ffmpeg/avformat.h>}).

@item Build your application, everything should work.

@end enumerate

@subsubsection Using shared libraries

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

@enumerate

@item Add a call to @file{vcvars32.bat} (which sets up the environment
variables for the Visual C++ tools) as the first line of @file{msys.bat}.
The standard location for @file{vcvars32.bat} is
@file{C:\Program Files\Microsoft Visual Studio 8\VC\bin\vcvars32.bat},
and the standard location for @file{msys.bat} is @file{C:\msys\1.0\msys.bat}.
If this corresponds to your setup, add the following line as the first line
of @file{msys.bat}:

@example
call "C:\Program Files\Microsoft Visual Studio 8\VC\bin\vcvars32.bat"
@end example

Alternatively, you may start the @file{Visual Studio 2005 Command Prompt},
and run @file{c:\msys\1.0\msys.bat} from there.

@item Within the MSYS shell, run @code{lib.exe}. If you get a help message
from @file{Microsoft (R) Library Manager}, this means your environment
variables are set up correctly, the @file{Microsoft (R) Library Manager}
is on the path and will be used by FFmpeg to create
MSVC++-compatible import libraries.

@item Build FFmpeg with

@example
./configure --enable-shared --enable-memalign-hack
make
make install
@end example

Your install path (@file{/usr/local/} by default) should now have the
necessary DLL and LIB files under the @file{bin} directory.

@end enumerate

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. @file{c:\msys\usr\local\bin}). This is not a typo, the LIB files are
installed in the @file{bin} directory. And instead of adding @file{libxx.a}
files, you should add @file{avcodec.lib}, @file{avformat.lib}, and
@file{avutil.lib}. There should be no need for @file{libmingwex.a},
@file{libgcc.a}, and @file{wsock32.lib}, nor any other external library
statically linked into the DLLs. The @file{bin} directory contains a bunch
of DLL files, but the ones that are actually used to run your application
are the ones with a major version number in their filenames
(i.e. @file{avcodec-51.dll}).

@subsection Cross compilation for Windows with Linux

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

Then configure FFmpeg with the following options:
@example
./configure --target-os=mingw32 --cross-prefix=i386-mingw32msvc-
@end example
(you can change the cross-prefix according to the prefix chosen for the
MinGW tools).

Then you can easily test FFmpeg with Wine
(@url{http://www.winehq.com/}).

@subsection Compilation under Cygwin

The main issue with Cygwin is that newlib, its C library, does not
contain llrint().  However, it is possible to leverage the
implementation in MinGW.

Just install your Cygwin with all the "Base" packages, plus the
following "Devel" ones:
@example
binutils, gcc-core, make, subversion, mingw-runtime
@end example

Do not install binutils-20060709-1 (they are buggy on shared builds);
use binutils-20050610-1 instead.

Then create a small library that just contains llrint():

@example
ar x /usr/lib/mingw/libmingwex.a llrint.o
ar cq /usr/local/lib/libllrint.a llrint.o
@end example

Then run

@example
./configure --enable-static --disable-shared  --extra-ldflags='-L /usr/local/lib' --extra-libs='-l llrint'
@end example

to make a static build or

@example
./configure --enable-shared --disable-static  --extra-ldflags='-L /usr/local/lib' --extra-libs='-l llrint'
@end example

to build shared libraries.

If you want to build FFmpeg with additional libraries, download Cygwin
"Devel" packages for Ogg and Vorbis from any Cygwin packages repository
and/or SDL, xvid, faac, faad2 packages from Cygwin Ports,
(@url{http://cygwinports.dotsrc.org/}).

@subsection 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:
@example
gcc-mingw-core, mingw-runtime, mingw-zlib
@end example

and add some special flags to your configure invocation.

For a static build run
@example
./configure --target-os=mingw32 --enable-memalign-hack --enable-static --disable-shared --extra-cflags=-mno-cygwin --extra-libs=-mno-cygwin
@end example

and for a build with shared libraries
@example
./configure --target-os=mingw32 --enable-memalign-hack --enable-shared --disable-static --extra-cflags=-mno-cygwin --extra-libs=-mno-cygwin
@end example

@section BeOS

BeOS support is broken in mysterious ways.

@section OS/2

For information about compiling FFmpeg on OS/2 see
@url{http://www.edm2.com/index.php/FFmpeg}.

@chapter Developers Guide

@section API
@itemize @bullet
@item libavcodec is the library containing the codecs (both encoding and
decoding). Look at @file{libavcodec/apiexample.c} to see how to use it.

@item libavformat is the library containing the file format handling (mux and
demux code for several formats). Look at @file{ffplay.c} to use it in a
player. See @file{output_example.c} to use it to generate audio or video
streams.

@end itemize

@section Integrating libavcodec or libavformat in your program

You can integrate all the source code of the libraries to link them
statically to avoid any version problem. All you need is to provide a
'config.mak' and a 'config.h' in the parent directory. See the defines
generated by ./configure to understand what is needed.

You can use libavcodec or libavformat in your commercial program, but
@emph{any patch you make must be published}. The best way to proceed is
to send your patches to the FFmpeg mailing list.

@node Coding Rules
@section Coding Rules

FFmpeg is programmed in the ISO C90 language with a few additional
features from ISO C99, namely:
@itemize @bullet
@item
the @samp{inline} keyword;
@item
@samp{//} comments;
@item
designated struct initializers (@samp{struct s x = @{ .i = 17 @};})
@item
compound literals (@samp{x = (struct s) @{ 17, 23 @};})
@end itemize

These features are supported by all compilers we care about, so we will not
accept patches to remove their use unless they absolutely do not impair
clarity and performance.

All code must compile with GCC 2.95 and GCC 3.3. Currently, FFmpeg also
compiles with several other compilers, such as the Compaq ccc compiler
or Sun Studio 9, and we would like to keep it that way unless it would
be exceedingly involved. To ensure compatibility, please do not use any
additional C99 features or GCC extensions. Especially watch out for: