FFmpeg是一個跨平台的影音編解碼函式庫，我們可以用來實作一個在Android平台上的 media player。首先先build出一個Android版本的FFmpeg。以下是這次我所用到的開發環境：- Cygwin- Android NDK：android-ndk-r4b-windows- FFmpeg：0.6.1《Step 1》在Android NDK上建立一個project。《Step 2》將FFmpeg的source code整包copy到 $(PROJECT)/jni 底下。《Step 3》在 $(PROJECT)/jni/ffmpeg 底下建立一個 config.sh：
#!/bin/bashPREBUILT=/android-ndk-r4b/build/prebuilt/windows/arm-eabi-4.4.0PLATFORM=/android-ndk-r4b/build/platforms/android-8/arch-arm./configure --target-os=linux / --arch=arm / --enable-version3 / --enable-gpl / --enable-nonfree / --disable-stripping / --disable-ffmpeg / --disable-ffplay / --disable-ffserver / --disable-ffprobe / --disable-encoders / --disable-muxers / --disable-devices / --disable-protocols / --enable-protocol=file / --enable-avfilter / --disable-network / --disable-mpegaudio-hp / --disable-avdevice / --enable-cross-compile / --cc=$PREBUILT/bin/arm-eabi-gcc / --cross-prefix=$PREBUILT/bin/arm-eabi- / --nm=$PREBUILT/bin/arm-eabi-nm / --extra-cflags="-fPIC -DANDROID" / --disable-asm / --enable-neon / --enable-armv5te / --extra-ldflags="-Wl,-T,$PREBUILT/arm-eabi/lib/ldscripts/armelf.x -Wl,-rpath-link=$PLATFORM/usr/lib -L$PLATFORM/usr/lib -nostdlib $PREBUILT/lib/gcc/arm-eabi/4.4.0/crtbegin.o $PREBUILT/lib/gcc/arm-eabi/4.4.0/crtend.o -lc -lm -ldl"PREBUILT和PLATFORM應該要符合你自己的配置。《Step 4》在Cygwin中，$(PROJECT)/jni/ffmpeg 底下執行config.sh：$ ./config.shconfigure會依據 config.sh內的設定將config.mak及config.h建立出來。《Step 5》在剛剛生成的 config.h中找到這句：#define restrict restrict因為Android的gcc並不認得restrict這個keyword，所以把它改寫 成：#define restrict《Step 6》將/libavutil/libm.h中所有的static函式，全都mark起來。《Step 7》分 別修改libavcodec、libavfilter、libavformat、libavutil、libpostproc和libswscale下的 Makefile，將下面兩句mark起來：include $(SUBDIR)../config.makinclude $(SUBDIR)../subdir.mak《Step 8》在$(PROJECT)/jni /ffmpeg下建立一個檔案av.mk，內容如下：
# LOCAL_PATH is one of libavutil, libavcodec, libavformat, or libswscaleinclude $(LOCAL_PATH)/../config.makOBJS :=OBJS-yes :=MMX-OBJS-yes :=include $(LOCAL_PATH)/Makefile# collect objectsOBJS-$(HAVE_MMX) += $(MMX-OBJS-yes)OBJS += $(OBJS-yes)FFNAME := lib$(NAME)FFLIBS := $(foreach,NAME,$(FFLIBS),lib$(NAME))FFCFLAGS = -DHAVE_AV_CONFIG_H -Wno-sign-compare -Wno-switch -Wno-pointer-signFFCFLAGS += -DTARGET_CONFIG=/"config-$(TARGET_ARCH).h/"ALL_S_FILES := $(wildcard $(LOCAL_PATH)/$(TARGET_ARCH)/*.S)ALL_S_FILES := $(addprefix $(TARGET_ARCH)/, $(notdir $(ALL_S_FILES)))ifneq ($(ALL_S_FILES),)ALL_S_OBJS := $(patsubst %.S,%.o,$(ALL_S_FILES))C_OBJS := $(filter-out $(ALL_S_OBJS),$(OBJS))S_OBJS := $(filter $(ALL_S_OBJS),$(OBJS))elseC_OBJS := $(OBJS)S_OBJS :=endifC_FILES := $(patsubst %.o,%.c,$(C_OBJS))S_FILES := $(patsubst %.o,%.S,$(S_OBJS))FFFILES := $(sort $(S_FILES)) $(sort $(C_FILES))《Step 9》在$(PROJECT)/jni底下修改Android.mk， 內容如下：include $(all-subdir-makefiles)《Step 10》在 /ffmpeg底下新增一個Android.mk：
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_STATIC_LIBRARIES := libavformat libavcodec libavutil libpostproc libswscale
LOCAL_MODULE := ffmpeg
include $(BUILD_SHARED_LIBRARY)
include $(call all-makefiles-under,$(LOCAL_PATH))《Step 11》在/ffmpeg /libavformat底下新增一個Android.mk：LOCAL_PATH := $(call my-dir)include $(CLEAR_VARS)include $(LOCAL_PATH)/../av.mkLOCAL_SRC_FILES := $(FFFILES)LOCAL_C_INCLUDES := / $(LOCAL_PATH) / $(LOCAL_PATH)/..LOCAL_CFLAGS += $(FFCFLAGS)LOCAL_CFLAGS += -include "string.h" -Dipv6mr_interface=ipv6mr_ifindexLOCAL_LDLIBS := -lzLOCAL_STATIC_LIBRARIES := $(FFLIBS)LOCAL_MODULE := $(FFNAME)include $(BUILD_STATIC_LIBRARY)《Step 12》在/ffmpeg/libavcodec 底下新增一個Android.mk：LOCAL_PATH := $(call my-dir)include $(CLEAR_VARS)include $(LOCAL_PATH)/../av.mkLOCAL_SRC_FILES := $(FFFILES)LOCAL_C_INCLUDES := / $(LOCAL_PATH) / $(LOCAL_PATH)/..LOCAL_CFLAGS += $(FFCFLAGS)LOCAL_LDLIBS := -lzLOCAL_STATIC_LIBRARIES := $(FFLIBS)LOCAL_MODULE := $(FFNAME)include $(BUILD_STATIC_LIBRARY)《Step 13》在libavfilter、 libavutil、libpostproc和libswscale底下都分別新增一個Android.mk：LOCAL_PATH := $(call my-dir)include $(CLEAR_VARS)
include $(LOCAL_PATH)/../av.mk
LOCAL_SRC_FILES := $(FFFILES)
LOCAL_C_INCLUDES := /
$(LOCAL_PATH) /
$(LOCAL_PATH)/..
LOCAL_CFLAGS += $(FFCFLAGS)
LOCAL_STATIC_LIBRARIES := $(FFLIBS)
LOCAL_MODULE := $(FFNAME)
include $(BUILD_STATIC_LIBRARY)《Step 14》在$(PROJECT) 底下執行ndk-build：$ /android-ndk-r4b/ndk-build《Step 15》完成，產 生出libavcodec.a、libavformat.a、libavutil.a、libpostproc.a、 libswscale.a和libffmpeg.so。
