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368 lines
17 KiB
368 lines
17 KiB
3 years ago
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# 前言
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FFmpeg是一个跨平台的多媒体库，也是目前音视频领域应用最广泛的库。包括libavcodec、libavformat、libavutil、</br>
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libavdevice、libavfilter、libswscale、libswresample、libpostproc等模块。其中avcodec用于编解码，</br>
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avformat用于解封装，avutil是提供工具类，avdevice用于各平台的设备接入，avfilter提供滤镜操作，</br>
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swscale提供图像缩放与像素格式转换，swresample提供音频重采样，postproc提供高级处理。</br>
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# 一、准备工作
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## 1、下载ffmpeg源码
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使用git命令：git clone https://github.com/FFmpeg/FFmpeg.git。
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## 2、下载ndk源码
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在Android开发者文档可以下载到ndk源码，[ndk下载链接](https://developer.android.com/ndk/downloads)。
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根据实际需求选择对应ndk版本，建议下载ndk-r20b稳定版。mac电脑配置ndk系统环境变量步骤如下：
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(1)、在命令行输入vim ~/.bash_profile
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(2)、输入i进行编辑模式
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(3)、编写export NDK_PATH=xxx/xxx/android-ndk-r20b
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(4)、按下esc退出编辑模式，输入:wq保存并退出
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# 二、编译ffmpeg源码
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## 1、分析configure结构
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在FFmpeg源码目录有个configure配置脚本，使用./configure --help进行查看，可以看到如下结构的编译选项：</br>
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| Help options: | Description |
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|:------------------------|:----------------------------|
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| --help | print this message |
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| --list-decoders | show all available decoders |
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| --list-encoders | show all available encoders |
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| --list-hwaccels | show all available hardware |
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| --list-demuxers | show all available demuxers |
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| --list-muxers | show all available muxers |
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| --list-parsers | show all available parsers |
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| --list-protocols | show all available protocols|
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| --list-filters | show all available filters |
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Licensing options:
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--enable-gpl allow use of GPL code [no]
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--enable-version3 upgrade (L)GPL to version 3 [no]
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--enable-nonfree allow use of nonfree code [no]
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Configuration options:
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--prefix=PREFIX install in PREFIX [/usr/local]
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--disable-static do not build static libraries [no]
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--enable-shared build shared libraries [no]
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--enable-small optimize for size instead of speed
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--disable-all disable components, libraries
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--disable-autodetect disable detected external libraries
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Program options:
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--disable-programs do not build command line programs
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--disable-ffmpeg disable ffmpeg build
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--disable-ffplay disable ffplay build
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--disable-ffprobe disable ffprobe build
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Component options:
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--disable-avdevice disable libavdevice build
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--disable-avcodec disable libavcodec build
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--disable-avformat disable libavformat build
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--disable-swresample disable libswresample build
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--disable-swscale disable libswscale build
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--disable-postproc disable libpostproc build
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--disable-avfilter disable libavfilter build
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--disable-pthreads disable pthreads
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--disable-network disable network support [no]
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Individual component options:
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--disable-everything disable all components
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--disable-encoder=NAME disable encoder NAME
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--enable-encoder=NAME enable encoder NAME
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--disable-encoders disable all encoders
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--disable-decoder=NAME disable decoder NAME
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--enable-decoder=NAME enable decoder NAME
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--disable-decoders disable all decoders
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--disable-muxer=NAME disable muxer NAME
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--enable-muxer=NAME enable muxer NAME
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--disable-muxers disable all muxers
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--disable-demuxer=NAME disable demuxer NAME
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--enable-demuxer=NAME enable demuxer NAME
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--disable-demuxers disable all demuxers
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--enable-parser=NAME enable parser NAME
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--disable-parser=NAME disable parser NAME
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--disable-parsers disable all parsers
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--enable-protocol=NAME enable protocol NAME
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--disable-protocol=NAME disable protocol NAME
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--disable-protocols disable all protocols
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--enable-filter=NAME enable filter NAME
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--disable-filter=NAME disable filter NAME
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--disable-filters disable all filters
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External library support:
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--disable-avfoundation disable Apple AVFoundation framework
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--enable-jni enable JNI support [no]
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--enable-libaom enable AV1 video codec via libaom [no]
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--enable-libass enable libass subtitles rendering [no]
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--enable-libdav1d enable AV1 decoding via libdav1d [no]
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--enable-libfdk-aac enable AAC de/encoding via libfdk-aac [no]
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--enable-libfontconfig enable libfontconfig [no]
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--enable-libfreetype enable libfreetype, needed for drawtext
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--enable-libfribidi enable libfribidi, improves drawtext filter
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--enable-libmp3lame enable MP3 encoding via libmp3lame [no]
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--enable-libopencv enable video filtering via libopencv [no]
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--enable-libopenh264 enable H.264 encoding via OpenH264 [no]
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--enable-libopus enable Opus de/encoding via libopus [no]
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--enable-librtmp enable RTMP[E] support via librtmp [no]
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--enable-libshine enable fixed-point MP3 encoding
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--enable-libsoxr enable Include libsoxr resampling [no]
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--enable-libspeex enable Speex de/encoding via libspeex [no]
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--enable-libtensorflow enable TensorFlow as a DNN module [no]
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--enable-libvorbis enable Vorbis en/decoding via libvorbis
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--enable-libvpx enable VP8 and VP9 de/encoding via libvpx
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--enable-libx264 enable H.264 encoding via x264 [no]
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--enable-libx265 enable HEVC encoding via x265 [no]
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--enable-mediacodec enable Android MediaCodec support [no]
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--enable-opengl enable OpenGL rendering [no]
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--enable-openssl enable openssl, needed for https support
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Toolchain options:
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--arch=ARCH select architecture []
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--cpu=CPU select the minimum required CPU
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--cross-prefix=PREFIX use PREFIX for compilation tools []
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--enable-cross-compile assume a cross-compiler is used
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--sysroot=PATH root of cross-build tree
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--target-os=OS compiler targets OS []
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--toolchain=NAME set tool defaults according to name
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--nm=NM use nm tool NM [nm -g]
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--ar=AR use archive tool AR [ar]
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--as=AS use assembler AS []
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--strip=STRIP use strip tool STRIP [strip]
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--cc=CC use C compiler CC [gcc]
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--cxx=CXX use C compiler CXX [g++]
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--ld=LD use linker LD []
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--host-cc=HOSTCC use host C compiler HOSTCC
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--host-cflags=HCFLAGS use HCFLAGS when compiling for host
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--host-ld=HOSTLD use host linker HOSTLD
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--host-ldflags=HLDFLAGS use HLDFLAGS when linking for host
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--host-extralibs=HLIBS use libs HLIBS when linking for host
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--host-os=OS compiler host OS []
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--extra-cflags=ECFLAGS add ECFLAGS to CFLAGS []
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--extra-cxxflags=ECFLAGS add ECFLAGS to CXXFLAGS []
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--extra-ldflags=ELDFLAGS add ELDFLAGS to LDFLAGS []
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## 2、修改so后缀
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默认编译出来的so库包括avcodec、avformat、avutil、avdevice、avfilter、swscale、</br>
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avresample、swresample、postproc，编译出来so是个软链接，真正so名字后缀带有一长串主版本号与子版本号，</br>
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这样的so名字在Adnroid平台无法识别。所以我们需要修改一下，打开该文件并搜索SLIBNAME，找到如下命令行：</br>
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```
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SLIBNAME_WITH_MAJOR='$(SLIBNAME).$(LIBMAJOR)'
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LIB_INSTALL_EXTRA_CMD='$$(RANLIB)"$(LIBDIR)/$(LIBNAME)"'
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SLIB_INSTALL_NAME='$(SLIBNAME_WITH_VERSION)'
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SLIB_INSTALL_LINKS='$(SLIBNAME_WITH_MAJOR)$(SLIBNAME)'
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```
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替换为：
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```
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SLIBNAME_WITH_MAJOR='$(SLIBPREF)$(FULLNAME)-$(LIBMAJOR)$(SLIBSUF)'
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LIB_INSTALL_EXTRA_CMD='$$(RANLIB)"$(LIBDIR)/$(LIBNAME)"'
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SLIB_INSTALL_NAME='$(SLIBNAME_WITH_MAJOR)'
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SLIB_INSTALL_LINKS='$(SLIBNAME)'
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```
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## 3、修改hevc_mvs.c
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在linux或者mac平台交叉编译过程中，可能在libavcodec/hevc_mvs.c报错：
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```
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libavcodec/hevc_mvs.c: In function 'derive_spatial_merge_candidates':
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libavcodec/hevc_mvs.c:208:15: error: 'y0000000' undeclared (first use in this function)
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((y ## v) >> s->ps.sps->log2_min_pu_size))
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^
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libavcodec/hevc_mvs.c:204:14: note: in definition of macro 'TAB_MVF'
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tab_mvf[(y) * min_pu_width + x]
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^
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libavcodec/hevc_mvs.c:274:16: note: in expansion of macro 'TAB_MVF_PU'
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(cand && !(TAB_MVF_PU(v).pred_flag == PF_INTRA))
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^
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libavcodec/hevc_mvs.c:368:23: note: in expansion of macro 'AVAILABLE'
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is_available_b0 = AVAILABLE(cand_up_right, B0) &&
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^
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libavcodec/hevc_mvs.c:208:15: note: each undeclared identifier is reported only once for each function it appears in
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((y ## v) >> s->ps.sps->log2_min_pu_size))
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^
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libavcodec/hevc_mvs.c:204:14: note: in definition of macro 'TAB_MVF'
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tab_mvf[(y) * min_pu_width + x]
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^
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libavcodec/hevc_mvs.c:274:16: note: in expansion of macro 'TAB_MVF_PU'
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(cand && !(TAB_MVF_PU(v).pred_flag == PF_INTRA))
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```
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原因是hevc_mvs.c会引用libavutil/timer.h文件(参考：ijkplayer#issues#4093)
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```
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#if CONFIG_LINUX_PERF
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#ifndef _GNU_SOURCE
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#define _GNU_SOURCE
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#endif
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#include <unistd.h>
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#include <sys/ioctl.h>
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#include <asm/unistd.h>
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#include <linux/perf_event.h>
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#endif
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```
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在sys/ioctl.h中最终会引用asm/termbits .h文件有#define B0 0000000，导致与hevc_mvs.c的B0命名冲突。</br>
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解决方法有2种：把B0改为b0、xB0改为xb0、yB0改为yb0。</br>
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或者在脚本添加：export COMMON_FF_CFG_FLAGS="$COMMON_FF_CFG_FLAGS --disable-linux-perf"</br>
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## 4、编译脚本
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在ffmpeg源码根目录创建一个shell脚本，比如命名为build_ffmpeg.sh，以mac编译环境为例，</br>
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ndk旧版本已经过时，google官方放弃了gcc交叉编译工具链，转而使用clang编译工具链，因为clang编译速度快、效率高。</br>
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下面例子是采用ndk新版的clang进行编译(如果是使用虚拟机在linux环境交叉编译FFmpeg，下面的darwin改为linux)。具体如下：</br>
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```
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#!/bin/bash
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make clean
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set -e
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archbit=64
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if [ $archbit -eq 64 ];then
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echo "build for 64bit"
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ARCH=aarch64
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CPU=armv8-a
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API=21
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PLATFORM=aarch64
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ANDROID=android
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CFLAGS=""
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LDFLAGS=""
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else
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echo "build for 32bit"
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ARCH=arm
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CPU=armv7-a
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API=16
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PLATFORM=armv7a
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ANDROID=androideabi
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CFLAGS="-mfloat-abi=softfp -march=$CPU"
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LDFLAGS="-Wl,--fix-cortex-a8"
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fi
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export NDK=/Users/xufulong/Library/Android/android-ndk-r20b
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export TOOLCHAIN=$NDK/toolchains/llvm/prebuilt/darwin-x86_64/bin
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export SYSROOT=$NDK/toolchains/llvm/prebuilt/darwin-x86_64/sysroot
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export CROSS_PREFIX=$TOOLCHAIN/$ARCH-linux-$ANDROID-
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export CC=$TOOLCHAIN/$PLATFORM-linux-$ANDROID$API-clang
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export CXX=$TOOLCHAIN/$PLATFORM-linux-$ANDROID$API-clang++
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export PREFIX=../ffmpeg-android/$CPU
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function build_android {
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./configure \
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--prefix=$PREFIX \
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--cross-prefix=$CROSS_PREFIX \
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--target-os=android \
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--arch=$ARCH \
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--cpu=$CPU \
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--cc=$CC \
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--cxx=$CXX \
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--nm=$TOOLCHAIN/$ARCH-linux-$ANDROID-nm \
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--strip=$TOOLCHAIN/$ARCH-linux-$ANDROID-strip \
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--enable-cross-compile \
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--sysroot=$SYSROOT \
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--extra-cflags="$CFLAGS" \
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--extra-ldflags="$LDFLAGS" \
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--extra-ldexeflags=-pie \
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--enable-runtime-cpudetect \
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--disable-static \
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--enable-shared \
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--disable-ffprobe \
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--disable-ffplay \
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--disable-ffmpeg \
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--disable-debug \
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--disable-doc \
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--enable-avfilter \
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--enable-avresample \
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--enable-decoders \
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$ADDITIONAL_CONFIGURE_FLAG
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make
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make install
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}
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build_android
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```
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按照上面shell脚本分为4段。第一段make clean清除缓存，set -e设置编译出错后马上退出，archbit=xx指定cpu架构是32位还是64位。</br>
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第二段if...else...fi用来条件编译不同cpu架构对应字段的值。第三段用export关键字声明宏定义，其中PREFIX是指定输出文件路径。</br>
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第四段是一个执行函数，按照ffmpeg的configure规范进行编写。函数里面的enable代表开启，disable代表关闭，也就是对ffmpeg进行剪裁，</br>
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根据我们需要的功能进行enable。make命令是执行编译，make install命令是执行安装。最后的build_android是执行函数。</br>
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初次执行shell脚本，需要修改脚本权限，使用linux命令：chmod 777 build_ffmpeg.sh。执行脚本只需要一行命令，</br>
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即在命令行输入./build_ffmpeg.sh。编译过程中，命令行会不断打印编译日志，等待命令行输出INSTALL xxx关键字代表编译完成。</br>
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## 5、编译问题分析
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编译过程中，可能会出现这样那样的问题，比如ndk配置不对、脚本语法不对。但不用慌，编译输出窗口会描述出错原因，</br>
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在ffbuild/config.log会告诉你问题的具体原因所在，顺着思路一般可以找到问题的答案。</br>
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# 三、so库剪裁
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ffmpeg强大之处在于支持按需编译，进行弹性剪裁。可以使用--disable-everything关闭所有模块，</br>
|
||
|
|
可以使用enable/disable来开启关闭某个模块，或者某个编解码器、某个封装器、某个协议。</br>
|
||
|
|
|
||
|
|
## 1、encoders与decoders
|
||
|
|
encoder和decoder在libavcodec模块，可以用./configure --list-encoders或者ffmpeg --encoders查看支持的编码器。</br>
|
||
|
|
同样地，可以用./configure --list-decoders或者ffmpeg --decoders查看支持的解码器。我们可以先--disable-encoders，</br>
|
||
|
|
--enable-encoder=aac,h264 其中lib开头的表示第三方库。</br>
|
||
|
|
|
||
|
|
## 2、muxers与demuxers
|
||
|
|
muxer和demuxer在libavformat模块，可用./configure --list-muxers或者ffmpeg --muxers查看支持的封装器。</br>
|
||
|
|
同样地，可用./configure --list-demuxers或者ffmpeg --demuxers查看支持的解封装器。先--disable-muxers，再--enable-muxer=mp3</br>
|
||
|
|
|
||
|
|
## 3、protocols
|
||
|
|
protocol也是在libavformat模块中，./configure --list-protocols或者ffmpeg --protocols查看支持的协议，</br>
|
||
|
|
|
||
|
|
## 4、parsers
|
||
|
|
parser在libavfilter模块中，提供各种filter，比如音频：amix、atempo，视频：rotate、hflip，</br>
|
||
|
|
我们可以根据需求--enable-parser来开启，可使用./configure --list-parsers查看具体列表。</br>
|
||
|
|
|
||
|
|
# 四、编译过程分析
|
||
|
|
编译过程包括：预编译、编译、汇编、链接。详细可以查阅书籍<程序员的自我修养>
|
||
|
|
|
||
|
|
## 1、预编译
|
||
|
|
预编译处理(.c/.cpp->.i)，对源文件的伪指令进行处理。
|
||
|
|
伪指令包括：宏定义(#define)、条件编译指令(#ifdef #elseif #endif)、头文件包含指令(#include)
|
||
|
|
|
||
|
|
## 2、编译
|
||
|
|
编译(.i->.s)，对经过预编译处理文件进行语法分析，编译为汇编文件。
|
||
|
|
|
||
|
|
## 3、汇编
|
||
|
|
汇编(.i->.o)，把汇编代码翻译为机器码，也就是二进制的目标文件。
|
||
|
|
|
||
|
|
## 4、链接
|
||
|
|
链接(.o->.so/.a/.lib)，把所有目标文件链接成动态库、静态库文件。
|
||
|
|
|
||
|
|
## 5、FFmpeg的makefile分析
|
||
|
|
makefile主要发生在汇编阶段，把所有依赖的目标文件添加进去。以FFmpeg的AVFilter模块makefile为例(有省略)：
|
||
|
|
```
|
||
|
|
NAME = avfilter
|
||
|
|
DESC = FFmpeg audio/video filtering library
|
||
|
|
|
||
|
|
HEADERS = avfilter.h \
|
||
|
|
buffersink.h \
|
||
|
|
buffersrc.h \
|
||
|
|
version.h \
|
||
|
|
|
||
|
|
OBJS = allfilters.o \
|
||
|
|
audio.o \
|
||
|
|
avfilter.o \
|
||
|
|
avfiltergraph.o \
|
||
|
|
buffersink.o \
|
||
|
|
buffersrc.o \
|
||
|
|
drawutils.o \
|
||
|
|
fifo.o \
|
||
|
|
formats.o \
|
||
|
|
framepool.o \
|
||
|
|
framequeue.o \
|
||
|
|
graphdump.o \
|
||
|
|
graphparser.o \
|
||
|
|
transform.o \
|
||
|
|
video.o \
|
||
|
|
|
||
|
|
# audio filters
|
||
|
|
OBJS-$(CONFIG_ACOPY_FILTER) += af_acopy.o
|
||
|
|
OBJS-$(CONFIG_ACROSSFADE_FILTER) += af_afade.o
|
||
|
|
OBJS-$(CONFIG_ACROSSOVER_FILTER) += af_acrossover.o
|
||
|
|
OBJS-$(CONFIG_ADELAY_FILTER) += af_adelay.o
|
||
|
|
OBJS-$(CONFIG_AECHO_FILTER) += af_aecho.o
|
||
|
|
|
||
|
|
# video filters
|
||
|
|
OBJS-$(CONFIG_BLACKDETECT_FILTER) += vf_blackdetect.o
|
||
|
|
OBJS-$(CONFIG_DEBLOCK_FILTER) += vf_deblock.o
|
||
|
|
OBJS-$(CONFIG_DELOGO_FILTER) += vf_delogo.o
|
||
|
|
OBJS-$(CONFIG_DRAWTEXT_FILTER) += vf_drawtext.o
|
||
|
|
OBJS-$(CONFIG_EDGEDETECT_FILTER) += vf_edgedetect.o
|
||
|
|
OBJS-$(CONFIG_EQ_FILTER) += vf_eq.o
|
||
|
|
OBJS-$(CONFIG_GBLUR_FILTER) += vf_gblur.o
|
||
|
|
OBJS-$(CONFIG_OVERLAY_FILTER) += vf_overlay.o framesync.o
|
||
|
|
```
|