# 编译FFmpeg

省略下载或同步源代码步骤，需要的源代码内容见[FFmpeg官方编译Wiki](https://trac.ffmpeg.org/wiki/CompilationGuide) 。为了后面编译动态库，编译时需要加上`-fPIC`参数。

## 编译需要的容器

```commandline
docker run -it -d --privileged=true --name centos7 -p 2333:22 centos:7 /usr/sbin/init
docker exec -it centos7 bash
```

## 编译

```shell
# 编译需要的环境
yum install autoconf automake bzip2 bzip2-devel freetype-devel gcc gcc-c++ git libtool make pkgconfig zlib-devel

# 解压源码
tar xzvf ffmpeg_sources.tar.gz
cd ~/ffmpeg_sources

# 解压
tar xjvf nasm-2.15.05.tar.bz2
tar xzvf yasm-1.3.0.tar.gz
tar xzvf lame-3.100.tar.gz
tar xzvf opus-1.3.1.tar.gz
tar zxvf libvpx.tar.gz -m # -m 强制时间同步
tar zxvf ffmpeg-4.4.tar.gz
tar zxvf x264-stable.tar.gz
mv x264-stable x264
tar zxvf x265_git.tar.gz
tar zxvf fdk-aac.tar.gz

# 安装cmake
./cmake-3.21.3-linux-x86_64.sh --prefix=/usr/local
mv /usr/local/cmake-3.21.3-linux-x86_64 /usr/local/cmake

# 添加编译需要的环境变量
echo "export PATH=\$PATH:/usr/local/cmake/bin" >> ~/.bashrc
echo "export PATH=\$HOME/bin:\$PATH" >> ~/.bashrc
echo "export PKG_CONFIG_PATH=\$HOME/ffmpeg_build/lib/pkgconfig:\$PKG_CONFIG_PATH" >> ~/.bashrc
source ~/.bashrc

# 编译nasm
cd ~/ffmpeg_sources/nasm-2.15.05
./autogen.sh
CFLAGS=-fPIC CPPFLAGS=-fPIC ./configure --prefix="$HOME/ffmpeg_build" --bindir="$HOME/bin"
make -j6 && make install

# 编译yasm
cd ~/ffmpeg_sources/yasm-1.3.0
CFLAGS=-fPIC CPPFLAGS=-fPIC ./configure --prefix="$HOME/ffmpeg_build" --bindir="$HOME/bin"
make -j6 && make install

# 编译x264
cd ~/ffmpeg_sources/x264
./configure --prefix="$HOME/ffmpeg_build" --bindir="$HOME/bin" --enable-static --extra-cflags=-fPIC
make -j6 && make install

# 编译x265
cd ~/ffmpeg_sources/x265_git/build/linux
cmake -G "Unix Makefiles" -DCMAKE_INSTALL_PREFIX="$HOME/ffmpeg_build" -DENABLE_SHARED:bool=off -DCMAKE_C_FLAGS=-fPIC -DCMAKE_CXX_FLAGS=-fPIC ../../source
make -j6 && make install

# 编译fdk-aac
cd ~/ffmpeg_sources/fdk-aac
autoreconf -fiv
CFLAGS=-fPIC CPPFLAGS=-fPIC ./configure --prefix="$HOME/ffmpeg_build" --disable-shared
make -j6 && make install

# 编译lame
cd ~/ffmpeg_sources/lame-3.100
CFLAGS=-fPIC CPPFLAGS=-fPIC ./configure --prefix="$HOME/ffmpeg_build" --bindir="$HOME/bin" --disable-shared --enable-nasm
make -j6 && make install

# 编译opus
cd ~/ffmpeg_sources/opus-1.3.1
CFLAGS=-fPIC CPPFLAGS=-fPIC ./configure --prefix="$HOME/ffmpeg_build" --disable-shared
make -j6 && make install

# 编译vpx
cd ~/ffmpeg_sources/libvpx
./configure --prefix="$HOME/ffmpeg_build" --disable-examples --disable-unit-tests --enable-vp9-highbitdepth --as=yasm --extra-cflags=-fPIC --extra-cxxflags=-fPIC
make -j6 && make install

# 编译ffmpeg
cd ~/ffmpeg_sources/ffmpeg-4.4
./configure \
  --prefix="$HOME/ffmpeg_build" \
  --pkg-config-flags="--static" \
  --extra-cflags="-I$HOME/ffmpeg_build/include -fPIC" \
  --extra-cxxflags="-fPIC" \
  --extra-ldflags="-L$HOME/ffmpeg_build/lib" \
  --extra-libs=-lpthread \
  --extra-libs=-lm \
  --bindir="$HOME/bin" \
  --enable-gpl \
  --enable-libfdk_aac \
  --enable-libfreetype \
  --enable-libmp3lame \
  --enable-libopus \
  --enable-libvpx \
  --enable-libx264 \
  --enable-libx265 \
  --enable-nonfree \
  --enable-shared
make -j6 && make install
```

如果`./configure`时去掉`--enable-shared`参数将会编译静态库。但使用FFmpeg编译的静态库的时候需要注意：**链接动态库**时要加上`-Wl,-Bsymbolic`选项，这个参数告诉链接器遇到重名符号时优先链接本地符号[^1]。否则将会出现错误：

```text
libavcodec.a(vc1dsp_mmx.o): relocation R_X86_64_PC32 against symbol `ff_pw_9' can not be used when making a shared object; recompile with -fPIC
```

# 编译OpenCV[^2]

```shell
yum install wget unzip
wget https://github.com/opencv/opencv/archive/4.5.3.zip
wget https://github.com/opencv/opencv_contrib/archive/refs/tags/4.5.3.zip -O 4.5.3_contrib.zip
unzip 4.5.3.zip
unzip 4.5.3_contrib.zip
cp -frap opencv_contrib-4.5.3/ opencv-4.5.3/
cd opencv-4.5.3/
mkdir build && cd build
cmake -DCMAKE_BUILD_TYPE=Release -DBUILD_SHARED_LIBS=OFF -DWITH_FFMPEG=ON -DCMAKE_SHARED_LINKER_FLAGS=-Wl,-Bsymbolic ../
make -j6 && make install
```

OpenCV 4.5.3 的FFmpeg的视频模块需要修改一处源代码，将OpenCV源码目录下的`modules/videoio/src/cap_ffmpeg_hw.hpp`文件939行`s_stream_ = std::istringstream(accel_list);`修改为`s_stream_.str(accel_list);`。

[^1]: 编译安装ffmpeg+OpenCV的时候的注意点 https://www.licc.tech/article?id=78

[^2]: Installation in Linux https://docs.opencv.org/master/d7/d9f/tutorial_linux_install.html