从demo分析ijk源码三：IjkMediaPlayer的jni实现

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。