回顾 mac系统 ijk（Android）编译，ijk的整个编译过程大致分为下载、编译ffmpeg、编译ijk，编译ffmpeg我们可以得到libijkffmpeg.so，编译ijk可以得到libijksdl.so和libijkplayer.so，编译ijk的时候需要依赖libijkffmpeg.so，这就是在ijk加载这三个so库的时候，为什么要先加载libijkffmpeg.so的原因。
下面以moudle ijkplayer-armv7a中的源码学习ijk中的jni实现，ijk c源码位于ijkplayer-armv7a/src/main/jni/目录下
如上图，jni目录下是c源码，obj目录下存放的是编译之后生成的文件，Android.mk 是提供给NDK编译的脚本。
一、Android.mk
LOCAL_PATH := $(call my-dir)
MY_APP_JNI_ROOT := $(realpath $(LOCAL_PATH))
MY_APP_PRJ_ROOT := $(realpath $(MY_APP_JNI_ROOT)/..)
MY_APP_ANDROID_ROOT := $(realpath $(MY_APP_PRJ_ROOT)/../../../..)
ifeq ($(TARGET_ARCH_ABI),armeabi-v7a)
MY_APP_FFMPEG_OUTPUT_PATH := $(realpath $(MY_APP_ANDROID_ROOT)/contrib/build/ffmpeg-armv7a/output)
MY_APP_FFMPEG_INCLUDE_PATH := $(realpath $(MY_APP_FFMPEG_OUTPUT_PATH)/include)
endif
ifeq ($(TARGET_ARCH_ABI),armeabi)
MY_APP_FFMPEG_OUTPUT_PATH := $(realpath $(MY_APP_ANDROID_ROOT)/contrib/build/ffmpeg-armv5/output)
MY_APP_FFMPEG_INCLUDE_PATH := $(realpath $(MY_APP_FFMPEG_OUTPUT_PATH)/include)
endif
ifeq ($(TARGET_ARCH_ABI),arm64-v8a)
MY_APP_FFMPEG_OUTPUT_PATH := $(realpath $(MY_APP_ANDROID_ROOT)/contrib/build/ffmpeg-arm64/output)
MY_APP_FFMPEG_INCLUDE_PATH := $(realpath $(MY_APP_FFMPEG_OUTPUT_PATH)/include)
endif
ifeq ($(TARGET_ARCH_ABI),x86)
MY_APP_FFMPEG_OUTPUT_PATH := $(realpath $(MY_APP_ANDROID_ROOT)/contrib/build/ffmpeg-x86/output)
MY_APP_FFMPEG_INCLUDE_PATH := $(realpath $(MY_APP_FFMPEG_OUTPUT_PATH)/include)
endif
ifeq ($(TARGET_ARCH_ABI),x86_64)
MY_APP_FFMPEG_OUTPUT_PATH := $(realpath $(MY_APP_ANDROID_ROOT)/contrib/build/ffmpeg-x86_64/output)
MY_APP_FFMPEG_INCLUDE_PATH := $(realpath $(MY_APP_FFMPEG_OUTPUT_PATH)/include)
endif
include $(call all-subdir-makefiles)
Android.mk通过 include $(call all-subdir-makefiles)调用编译所有子目录的mk文件
二、ijkplayer_jni.c
ijkplayer_jni.c在Android Studio中的路径是
ijkplayer-android/android/ijkplayer/ijkplayer-armv7a/src/main/jni/ijkmedia/ijkplayer/android/ijkplayer_jni.c，这个路径其实是个软链，其真实存放路径为 ijkplayer-android/ijkmedia/ijkplayer/android/ijkplayer_jni.c。
ijkplayer_jni.c文件中包含所有的在IjkMediaPlayer中定义的native方法的c实现。
static JNINativeMethod g_methods[] = {
{
"_setDataSource",
"(Ljava/lang/String;[Ljava/lang/String;[Ljava/lang/String;)V",
(void *) IjkMediaPlayer_setDataSourceAndHeaders
},
{ "_setDataSourceFd", "(I)V", (void *) IjkMediaPlayer_setDataSourceFd },
{ "_setDataSource", "(Ltv/danmaku/ijk/media/player/misc/IMediaDataSource;)V", (void *)IjkMediaPlayer_setDataSourceCallback },
{ "_setAndroidIOCallback", "(Ltv/danmaku/ijk/media/player/misc/IAndroidIO;)V", (void *)IjkMediaPlayer_setAndroidIOCallback },
{ "_setVideoSurface", "(Landroid/view/Surface;)V", (void *) IjkMediaPlayer_setVideoSurface },
{ "_prepareAsync", "()V", (void *) IjkMediaPlayer_prepareAsync },
{ "_start", "()V", (void *) IjkMediaPlayer_start },
{ "_stop", "()V", (void *) IjkMediaPlayer_stop },
{ "seekTo", "(J)V", (void *) IjkMediaPlayer_seekTo },
{ "_pause", "()V", (void *) IjkMediaPlayer_pause },
{ "isPlaying", "()Z", (void *) IjkMediaPlayer_isPlaying },
{ "getCurrentPosition", "()J", (void *) IjkMediaPlayer_getCurrentPosition },
{ "getDuration", "()J", (void *) IjkMediaPlayer_getDuration },
{ "_release", "()V", (void *) IjkMediaPlayer_release },
{ "_reset", "()V", (void *) IjkMediaPlayer_reset },
{ "setVolume", "(FF)V", (void *) IjkMediaPlayer_setVolume },
{ "getAudioSessionId", "()I", (void *) IjkMediaPlayer_getAudioSessionId },
{ "native_init", "()V", (void *) IjkMediaPlayer_native_init },
{ "native_setup", "(Ljava/lang/Object;)V", (void *) IjkMediaPlayer_native_setup },
{ "native_finalize", "()V", (void *) IjkMediaPlayer_native_finalize },
{ "_setOption", "(ILjava/lang/String;Ljava/lang/String;)V", (void *) IjkMediaPlayer_setOption },
{ "_setOption", "(ILjava/lang/String;J)V", (void *) IjkMediaPlayer_setOptionLong },
{ "_getColorFormatName", "(I)Ljava/lang/String;", (void *) IjkMediaPlayer_getColorFormatName },
{ "_getVideoCodecInfo", "()Ljava/lang/String;", (void *) IjkMediaPlayer_getVideoCodecInfo },
{ "_getAudioCodecInfo", "()Ljava/lang/String;", (void *) IjkMediaPlayer_getAudioCodecInfo },
{ "_getMediaMeta", "()Landroid/os/Bundle;", (void *) IjkMediaPlayer_getMediaMeta },
{ "_setLoopCount", "(I)V", (void *) IjkMediaPlayer_setLoopCount },
{ "_getLoopCount", "()I", (void *) IjkMediaPlayer_getLoopCount },
{ "_getPropertyFloat", "(IF)F", (void *) ijkMediaPlayer_getPropertyFloat },
{ "_setPropertyFloat", "(IF)V", (void *) ijkMediaPlayer_setPropertyFloat },
{ "_getPropertyLong", "(IJ)J", (void *) ijkMediaPlayer_getPropertyLong },
{ "_setPropertyLong", "(IJ)V", (void *) ijkMediaPlayer_setPropertyLong },
{ "_setStreamSelected", "(IZ)V", (void *) ijkMediaPlayer_setStreamSelected },
{ "native_profileBegin", "(Ljava/lang/String;)V", (void *) IjkMediaPlayer_native_profileBegin },
{ "native_profileEnd", "()V", (void *) IjkMediaPlayer_native_profileEnd },
{ "native_setLogLevel", "(I)V", (void *) IjkMediaPlayer_native_setLogLevel },
{ "_setFrameAtTime", "(Ljava/lang/String;JJII)V", (void *) IjkMediaPlayer_setFrameAtTime },
};
JNIEXPORT jint JNI_OnLoad(JavaVM *vm, void *reserved)
{
JNIEnv* env = NULL;
g_jvm = vm;
if ((*vm)->GetEnv(vm, (void**) &env, JNI_VERSION_1_4) != JNI_OK) {
return -1;
}
assert(env != NULL);
pthread_mutex_init(&g_clazz.mutex, NULL );
// FindClass returns LocalReference
IJK_FIND_JAVA_CLASS(env, g_clazz.clazz, JNI_CLASS_IJKPLAYER);
(*env)->RegisterNatives(env, g_clazz.clazz, g_methods, NELEM(g_methods) );
ijkmp_global_init();
ijkmp_global_set_inject_callback(inject_callback);
FFmpegApi_global_init(env);
return JNI_VERSION_1_4;
}
JNIEXPORT void JNI_OnUnload(JavaVM *jvm, void *reserved)
{
ijkmp_global_uninit();
pthread_mutex_destroy(&g_clazz.mutex);
}
我们可以从这里入手学习ijk是如何调用ffplay实现播放的。
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