ffmpeg编译so

1.第一个坑：/bin/bash^M: bad interpreter: No such file or directory

shell脚本报错/bin/bash^M: bad interpreter: No such file or directory，通过查阅资料得知，shell脚本格式必须是unix才行，但我这个脚本是在windows上编写完成传到Linux服务器上的，所以一执行就报错

windows环境下的文件是dos格式，即每行结尾以\r\n来标识，而linux下的文件是unix格式，行尾则以\n来标识

查看文件是dos还是unix的格式的方法：

1.cat -A filename，如果输出结果中行末是^M$，则是dos格式 ，如果行末只是$，则是unix格式。

2.vim filename，编辑文件，执行“:set ff”,若执行结果为fileformat=dos则为dos格式，若执行结果为fileformat=unix则为unix格式。

3.od -t x1 filename，以16进制查看文件，若输出结果中存在“0d 0a”则为dos格式，如果只有“0a”则为unix格式。其中“0d”即为回车符“\r”，“0a”即为换行符“\n”。

文件格式转换：

1.sed -i “s/\r//” filename 或sed -i “s/^M//” filename，直接将回车符替换为空字符串。

2.vim filename，编辑文件，执行“: set ff=unix”，将文件设置为unix格式，然后执行“:wq”，保存退出。

3.dos2unix filename或busybox dos2unix filename

转换成unix格式就可以正常运行脚本了

 2.编译so

脚本

#!/bin/bash
make clean 
#填写你具体的ndk解压目录  建议用相对路径
export NDK=../android-ndk-r20b
export SYSROOT=$NDK/platforms/android-28/arch-arm/
export TOOLCHAIN=$NDK/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64
export CPU=arm
#编译后的文件会放置在 当前路径下的android/arm下
export PREFIX=$(pwd)/android/$CPU
export ADDI_CFLAGS="-marm"
 
 
#./configure 即为ffmpeg 根目录下的可执行文件configure
#你可以在ffmpeg根目录下使用./configure --hellp 查看 ./configure后可填入的参数。
 
./configure --target-os=linux \
    --prefix=$PREFIX --arch=arm \
    --disable-doc \
    --enable-shared \
    --disable-static \
    --disable-yasm \
    --disable-symver \
    --enable-gpl \
    --disable-ffmpeg \
    --disable-ffplay \
    --disable-ffprobe \
    --disable-ffserver \
    --disable-doc \
    --disable-symver \
    --cross-prefix=$TOOLCHAIN/bin/arm-linux-androideabi- \
    --enable-cross-compile \
    --sysroot=$SYSROOT \
    --extra-cflags="-Os -fpic $ADDI_CFLAGS" \
    --extra-ldflags="$ADDI_CFLAGS" \
    $ADDITIONAL_CONFIGURE_FLAG
make clean
make
make install

编译成功会生成如下目录

 include是头文件  lib是so库

遇到的问题

1.编译FFMPEG时，出现了错误 nasm/yasm not found or too old. Use --disable-x86asm for a crippled build. 

原因
这是因为 FFMPEG为了提高编译速度，使用了汇编指令，如MMX和SSE等。如果系统中没有yasm指令的话，就会该错误。

解决办法
安装yasm。

安装yasm
Windows系统安装yasm
如果是Windows系统， 从网上下载一个 yasm.exe 并安装在mingw/bin下面，重新编译，就不会出现该错误了。

Linux系统安装yasm
如果是Linux系统，则更简单，直接在终端输入 yum install yasm , 安装好后，重新编译就 OK了。

除了使用yum安装yasm，还可以编译安装，如下：
在http://www.tortall.net/projects/yasm/releases下面找到适合自己平台的yasm版本。然后进行安装。举例如下：

1）下载：wget http://www.tortall.net/projects/yasm/releases/yasm-1.3.0.tar.gz

2）解压：tar zxvf yasm-1.3.0.tar.gz

3）切换路径： cd yasm-1.3.0

4）执行配置： ./configure

5）编译：make

6）安装：make install
 

2.执行脚本报错 缺少文件

root@realbom2-PowerEdge-R730xd:/lv1/wanglongjiang/ffmpeg/ffmpeg-6.0# ./build.sh
Makefile:2: ffbuild/config.mak: No such file or directory
Makefile:42: /tools/Makefile: No such file or directory
Makefile:43: /ffbuild/common.mak: No such file or directory
Makefile:113: /libavutil/Makefile: No such file or directory
Makefile:113: /ffbuild/library.mak: No such file or directory
Makefile:115: /fftools/Makefile: No such file or directory
Makefile:116: /doc/Makefile: No such file or directory
Makefile:117: /doc/examples/Makefile: No such file or directory
Makefile:184: /tests/Makefile: No such file or directory
make: *** No rule to make target '/tests/Makefile'.  Stop.
Unknown option "--disable-ffserver".
See ./configure --help for available options.
Makefile:2: ffbuild/config.mak: No such file or directory
Makefile:42: /tools/Makefile: No such file or directory
Makefile:43: /ffbuild/common.mak: No such file or directory
Makefile:113: /libavutil/Makefile: No such file or directory
Makefile:113: /ffbuild/library.mak: No such file or directory
Makefile:115: /fftools/Makefile: No such file or directory
Makefile:116: /doc/Makefile: No such file or directory
Makefile:117: /doc/examples/Makefile: No such file or directory
Makefile:184: /tests/Makefile: No such file or directory
make: *** No rule to make target '/tests/Makefile'.  Stop.
Makefile:2: ffbuild/config.mak: No such file or directory
Makefile:42: /tools/Makefile: No such file or directory
Makefile:43: /ffbuild/common.mak: No such file or directory
Makefile:113: /libavutil/Makefile: No such file or directory
Makefile:113: /ffbuild/library.mak: No such file or directory
Makefile:115: /fftools/Makefile: No such file or directory
Makefile:116: /doc/Makefile: No such file or directory
Makefile:117: /doc/examples/Makefile: No such file or directory
Makefile:184: /tests/Makefile: No such file or directory
make: *** No rule to make target '/tests/Makefile'.  Stop.
Makefile:2: ffbuild/config.mak: No such file or directory
Makefile:42: /tools/Makefile: No such file or directory
Makefile:43: /ffbuild/common.mak: No such file or directory
Makefile:113: /libavutil/Makefile: No such file or directory
Makefile:113: /ffbuild/library.mak: No such file or directory
Makefile:115: /fftools/Makefile: No such file or directory
Makefile:116: /doc/Makefile: No such file or directory
Makefile:117: /doc/examples/Makefile: No such file or directory
Makefile:184: /tests/Makefile: No such file or directory
make: *** No rule to make target '/tests/Makefile'.  Stop.

解决方法：
先不要执行make和make install，先在ffmpeg目录下执行./configure，该命令会自动生成缺少的文件