在FFmpeg源码下增加自定义程序

为了了解FFmpeg解码的细节，使用avcodec_send_packet和avcodec_receive_frame组合，写了一个简单的例子，解码video生成yuv文件，比起用FFmpeg跟踪代码要简单很多。

但是问题是在FFmpeg下编译的ffmpeg/ffplay都可以直接跟踪调试，自己编译的因为连接的系统的动态库，所以不能跟踪到代码里面。

所以参考tools/enum_options程序，在FFmpeg源码目录新增一个目录，修改Makefile相关代码，就可以编译生成类似ffmpeg/ffplay的可执行文件，放在vscode里面非常方便的展台调试。

STEP 1：增加decode目录

decode/
├── decode3.c
└── Makefile

如果是直接编译，链接系统库，没法gdb调试FFmpeg源码，试了下make tools/enum_options可以生成enum_options程序，并且gdb可以调试FFmpeg源码，所以参考tools/Makefile，decode/Makefile如下：

STEP 2：Makefile

DECODE = decode3OUTDIRS += decodeclean::$(RM) $(CLEANSUFFIXES:%=decode/%)

STEP 3：添加到FFmpeg/Makefile

将这个Makefile还要加入到FFmpeg/Makefile里面，下面是diff文件，为了知道每个变量的内容，增加了info打印：

--- a/Makefile
+++ b/Makefile
@@ -39,13 +39,29 @@ SKIPHEADERS = compat/w32pthreads.h# first so "all" becomes default targetall: all-yes+# decode3
+include $(SRC_PATH)/tools/Makefile
+include $(SRC_PATH)/decode/Makefileinclude $(SRC_PATH)/ffbuild/common.makFF_EXTRALIBS := $(FFEXTRALIBS)FF_DEP_LIBS  := $(DEP_LIBS)FF_STATIC_DEP_LIBS := $(STATIC_DEP_LIBS)+$(info debug - info FF_EXTRALIBS: $(FF_EXTRALIBS))
+$(info debug - info FF_DEP_LIBS: $(FF_DEP_LIBS))
+$(info debug - info DEP_LIBS: $(DEP_LIBS))
+$(info debug - info LD_O: $(LD_O))
+$(info debug - info LDFLAGS: $(LDFLAGS))
+$(info debug - info LDEXEFLAGS: $(LDEXEFLAGS))
+$(info debug - info EXTRALIBS: $(EXTRALIBS))
+$(info debug - info ELIBS: $(ELIBS))
+$(info debug - info LD: $(LD))
+$(info debug - info EXESUF: $(EXESUF))
+$(info debug - info DECODE: $(DECODE))
+$(info debug - info LIBFUZZER_PATH: $(LIBFUZZER_PATH))
+$(TOOLS): %$(EXESUF): %.o$(LD) $(LDFLAGS) $(LDEXEFLAGS) $(LD_O) $^ $(EXTRALIBS-$(*F)) $(EXTRALIBS) $(ELIBS)@@ -64,6 +80,8 @@ tools/target_dem_fuzzer$(EXESUF): tools/target_dem_fuzzer.o $(FF_DEP_LIBS)tools/target_io_dem_fuzzer$(EXESUF): tools/target_io_dem_fuzzer.o $(FF_DEP_LIBS)$(LD) $(LDFLAGS) $(LDEXEFLAGS) $(LD_O) $^ $(ELIBS) $(FF_EXTRALIBS) $(LIBFUZZER_PATH)+decode/decode3$(EXESUF): decode/decode3.o $(FF_DEP_LIBS)
+       $(LD) $(LDFLAGS) $(LDEXEFLAGS) $(LD_O) $^ $(ELIBS) $(FF_EXTRALIBS) $(LIBFUZZER_PATH)tools/enum_options$(EXESUF): ELIBS = $(FF_EXTRALIBS)tools/enum_options$(EXESUF): $(FF_DEP_LIBS)

STEP 4：编译

这样编译就可以生成decode3，奇怪的是得先make decode，然后再make decode3

$ make decode
debug - info FF_EXTRALIBS: -lavdevice -lavfilter -lavformat -lavcodec -lpostproc -lswresample -lswscale -lavutil  -lm -latomic -lxcb -lxcb-shm -lxcb-shape -lxcb-xfixes -lasound -lSDL2 -lsndio -lXv -lX11 -lXext -pthread -lm -latomic -lva -lm -latomic -lz -pthread -lm -latomic -llzma -L/usr/local/lib/x86_64-linux-gnu -llc3 -L/usr/local/lib/x86_64-linux-gnu -lopus -L/usr/local/lib -lx264 -L/usr/local/lib/x86_64-linux-gnu -lopenh264 -lz -lva -lm -latomic -lm -latomic -lm -latomic -pthread -lva-drm -lva -lva-x11 -lva -lvdpau -lX11 -lm -lva -latomic -lX11 
debug - info FF_DEP_LIBS: libavdevice/libavdevice.a libavfilter/libavfilter.a libavformat/libavformat.a libavcodec/libavcodec.a libpostproc/libpostproc.a libswresample/libswresample.a libswscale/libswscale.a libavutil/libavutil.a
debug - info DEP_LIBS: libavdevice/libavdevice.a libavfilter/libavfilter.a libavformat/libavformat.a libavcodec/libavcodec.a libpostproc/libpostproc.a libswresample/libswresample.a libswscale/libswscale.a libavutil/libavutil.a
debug - info LD_O: -o 
debug - info LDFLAGS: -Llibavcodec -Llibavdevice -Llibavfilter -Llibavformat -Llibavutil -Llibpostproc -Llibswscale -Llibswresample -Wl,--as-needed -Wl,-z,noexecstack -Wl,--warn-common -Wl,-rpath-link=:libpostproc:libswresample:libswscale:libavfilter:libavdevice:libavformat:libavcodec:libavutil
debug - info LDEXEFLAGS: 
debug - info EXTRALIBS: 
debug - info ELIBS: 
debug - info LD: @printf "LD\t%s\n" ; gcc
debug - info EXESUF: 
debug - info DECODE: decode3
debug - info LIBFUZZER_PATH: 
Current directory: ffmpeg ffplay ffprobe$ make decode/decode3
debug - info FF_EXTRALIBS: -lavdevice -lavfilter -lavformat -lavcodec -lpostproc -lswresample -lswscale -lavutil  -lm -latomic -lxcb -lxcb-shm -lxcb-shape -lxcb-xfixes -lasound -lSDL2 -lsndio -lXv -lX11 -lXext -pthread -lm -latomic -lva -lm -latomic -lz -pthread -lm -latomic -llzma -L/usr/local/lib/x86_64-linux-gnu -llc3 -L/usr/local/lib/x86_64-linux-gnu -lopus -L/usr/local/lib -lx264 -L/usr/local/lib/x86_64-linux-gnu -lopenh264 -lz -lva -lm -latomic -lm -latomic -lm -latomic -pthread -lva-drm -lva -lva-x11 -lva -lvdpau -lX11 -lm -lva -latomic -lX11 
debug - info FF_DEP_LIBS: libavdevice/libavdevice.a libavfilter/libavfilter.a libavformat/libavformat.a libavcodec/libavcodec.a libpostproc/libpostproc.a libswresample/libswresample.a libswscale/libswscale.a libavutil/libavutil.a
debug - info DEP_LIBS: libavdevice/libavdevice.a libavfilter/libavfilter.a libavformat/libavformat.a libavcodec/libavcodec.a libpostproc/libpostproc.a libswresample/libswresample.a libswscale/libswscale.a libavutil/libavutil.a
debug - info LD_O: -o 
debug - info LDFLAGS: -Llibavcodec -Llibavdevice -Llibavfilter -Llibavformat -Llibavutil -Llibpostproc -Llibswscale -Llibswresample -Wl,--as-needed -Wl,-z,noexecstack -Wl,--warn-common -Wl,-rpath-link=:libpostproc:libswresample:libswscale:libavfilter:libavdevice:libavformat:libavcodec:libavutil
debug - info LDEXEFLAGS: 
debug - info EXTRALIBS: 
debug - info ELIBS: 
debug - info LD: @printf "LD\t%s\n" ; gcc
debug - info EXESUF: 
debug - info DECODE: decode3
debug - info LIBFUZZER_PATH: 
Current directory: ffmpeg ffplay ffprobe
CC      decode/decode3.o
LD      decode/decode3

没有decode目录，make decode/decode3会报错，手动创建decode目录也是可以的。

不然会报错：

src/decode/decode3.c: At top level:
src/decode/decode3.c:165:1: fatal error: opening dependency file decode/decode3.d: No such file or directory165 | }| ^
compilation terminated.
make: *** [src/ffbuild/common.mak:81: decode/decode3.o] Error 1

decode/Makefile中已经定义了OUTDIRS += decode，检查FFmpeg/Makefile中的OUTDIRS有：

$(sort $(OUTDIRS)):$(Q)mkdir -p $@

所以从这里判断make clean，重新make后应该可以直接make decode/decode3，试了下果然可以了。

STEP 5：运行调试

查找decode3的符号可以发现，这个是包含了所有FFmpeg的代码，不需要加载FFmpeg的动态库，所以FFmpeg中的源码更新后直接make decode/decode3即可。

$ nm decode3 |  grep -E "avcodec_send_packet|avcodec_receive_frame|av_read_frame"
000000000031dd95 T avcodec_receive_frame
000000000041a5b6 T avcodec_send_packet
000000000009ea7c T av_read_frame

ldd也可以确定这一点：

$ ldd decode3linux-vdso.so.1 (0x00007ffe27536000)libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f04eadf4000)libdrm.so.2 => /usr/lib/x86_64-linux-gnu/libdrm.so.2 (0x00007f04eabe3000)libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007f04ea9c6000)libopus.so.0 => /usr/local/lib/x86_64-linux-gnu/libopus.so.0 (0x00007f04ea76f000)libx264.so.152 => /usr/lib/x86_64-linux-gnu/libx264.so.152 (0x00007f04ea3ca000)libopenh264.so.7 => /usr/local/lib/x86_64-linux-gnu/libopenh264.so.7 (0x00007f04ea0b4000)libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f04e9e95000)libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f04e9aa4000)/lib64/ld-linux-x86-64.so.2 (0x00007f04edef6000)libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f04e98a0000)libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f04e9440000)libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f04e921d000)

vscode launch.json

vscode中的 launch.json中修改program和args即可以运行调试。

{// Use IntelliSense to learn about possible attributes.// Hover to view descriptions of existing attributes.// For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387"version": "0.2.0","configurations": [{"name": "(gdb) Launch","type": "cppdbg","request": "launch","program": "${workspaceFolder}/build/decode/decode3","args": ["${workspaceFolder}/decode/256x144.mp4", "${workspaceFolder}/decode/256x144-yuv420p.yuv"],"stopAtEntry": false,"cwd": "${workspaceFolder}/","environment": [ ],"externalConsole": false,"MIMode": "gdb","setupCommands": [{"description": "Enable pretty-printing for gdb","text": "-enable-pretty-printing","ignoreFailures": true},{"description": "Set Disassembly Flavor to Intel","text": "-gdb-set disassembly-flavor intel","ignoreFailures": true}]}]
}