在Android中MediaPlayer用来播放音频和视频文件，在这里分析下在Framework层中MediaPlayer是如何调用的，MediaPlayer的代码位于：.／frameworks/base/media/java/android/media/MediaPlayer.java 下面用到的代码是基于Android 4.4
打开后有一个静态代码块是加载库文件的，只要这个类被创建就会加载库。
static {
System.loadLibrary("media_jni");
native_init();
}libmedia_jni.so的源代码位于：./frameworks/base/media/jni
在jni这个文件夹中有个makefile文件 Android.mk
LOCAL_PATH:= $(call my-dir) include $(CLEAR_VARS) LOCAL_SRC_FILES:= android_media_ImageReader.cpp android_media_MediaCrypto.cpp android_media_MediaCodec.cpp android_media_MediaCodecList.cpp android_media_MediaDrm.cpp android_media_MediaExtractor.cpp android_media_MediaMuxer.cpp android_media_MediaPlayer.cpp android_media_MediaRecorder.cpp android_media_MediaScanner.cpp android_media_MediaMetadataRetriever.cpp android_media_ResampleInputStream.cpp android_media_MediaProfiles.cpp android_media_AmrInputStream.cpp android_media_Utils.cpp android_mtp_MtpDatabase.cpp android_mtp_MtpDevice.cpp android_mtp_MtpServer.cpp LOCAL_SHARED_LIBRARIES := libandroid_runtime libnativehelper libutils libbinder libmedia libskia libui liblog libcutils libgui libstagefright libstagefright_foundation libcamera_client libmtp libusbhost libexif libstagefright_amrnb_common LOCAL_REQUIRED_MODULES := libjhead_jni LOCAL_STATIC_LIBRARIES := libstagefright_amrnbenc LOCAL_C_INCLUDES += external/libexif/ external/tremor/Tremor frameworks/base/core/jni frameworks/av/media/libmedia frameworks/av/media/libstagefright frameworks/av/media/libstagefright/codecs/amrnb/enc/src frameworks/av/media/libstagefright/codecs/amrnb/common frameworks/av/media/libstagefright/codecs/amrnb/common/include $(TOP)/mediatek/external/amr frameworks/av/media/mtp frameworks/native/include/media/openmax $(call include-path-for, libhardware)/hardware system/media/camera/include $(PV_INCLUDES) $(JNI_H_INCLUDE) $(call include-path-for, corecg graphics) ifeq ($(strip $(MTK_TB_DEBUG_SUPPORT)),yes) LOCAL_C_INCLUDES += $(MTK_PATH_SOURCE)/frameworks/base/include endif ifeq ($(strip $(MTK_HIGH_QUALITY_THUMBNAIL)),yes) LOCAL_CFLAGS += -DMTK_HIGH_QUALITY_THUMBNAIL endif ifeq ($(strip $(MTK_USE_ANDROID_MM_DEFAULT_CODE)),yes) LOCAL_CFLAGS += -DANDROID_DEFAULT_CODE endif LOCAL_CFLAGS += LOCAL_LDLIBS := -lpthread LOCAL_MODULE:= libmedia_jni include $(BUILD_SHARED_LIBRARY) # build libsoundpool.so # build libaudioeffect_jni.so include $(call all-makefiles-under,$(LOCAL_PATH))LOCAL_MODULE:= libmedia_jni 编译后会生成libmedia_jni库
打开文件有四个重载函数
setDataSource (String path)
setDataSource (FileDescriptor fd)
setDataSource (Context context, Uri uri)
setDataSource (FileDescriptor fd, long offset, long length)
在APP中，如原生的Music
/**
* M: add async prepare to aviod ANR, add information and duration update listener
*
* @param player The mediaplayer
* @param path The data source path
* @param async M: use async prepare if it's set true .
* @return If set data source success, return true, otherwise false.
*/
private boolean setDataSourceImpl(MediaPlayer player, String path, boolean async) {
MusicLogUtils.d(TAG, "setDataSourceImpl(" + path + ");async = " + async);
try {
player.reset();
if (async) {
player.setOnPreparedListener(preparedlistener);
} else {
player.setOnPreparedListener(null);
}
if (path.startsWith("content://")) {
player.setDataSource(MediaPlaybackService.this, Uri.parse(path));
} else {
// / M: add add for DRM secure flag @{
MediaPlayerEx.setContextForSecureFlag(player,
MediaPlaybackService.this.getApplicationContext());
// / @}
player.setDataSource(path);
}
/// M: Attach auxiliary audio effect only with valid effect id
if (mAuxEffectId > 0) {
player.attachAuxEffect(mAuxEffectId);
player.setAuxEffectSendLevel(1.0f);
mWhetherAttachWhenPause = false;
MusicLogUtils.d(TAG, "setDataSourceImpl: attachAuxEffect mAuxEffectId = " + mAuxEffectId);
}
player.setAudioStreamType(AudioManager.STREAM_MUSIC);
if (async) {
player.prepareAsync();
} else {
player.prepare();
}
} catch (IOException ex) {
// TODO: notify the user why the file couldn't be opened
MusicLogUtils.e(TAG, "setDataSourceImpl: " + ex);
return false;
} catch (IllegalArgumentException ex) {
// TODO: notify the user why the file couldn't be opened
MusicLogUtils.e(TAG, "setDataSourceImpl: " + ex);
return false;
} catch (IllegalStateException ex) {
MusicLogUtils.e(TAG, "setDataSourceImpl: " + ex);
return false;
}
player.setOnCompletionListener(listener);
player.setOnErrorListener(errorListener);
player.setOnInfoListener(infoListener);
player.setOnDurationUpdateListener(durationListener);
sendSessionIdToAudioEffect(false);
return true;
}不管在App中调用的是哪个函数，最后在MediaPlayer.java中都是调用
/**
* Sets the data source (FileDescriptor) to use. The FileDescriptor must be
* seekable (N.B. a LocalSocket is not seekable). It is the caller's responsibility
* to close the file descriptor. It is safe to do so as soon as this call returns.
*
* @param fd the FileDescriptor for the file you want to play
* @param offset the offset into the file where the data to be played starts, in bytes
* @param length the length in bytes of the data to be played
* @throws IllegalStateException if it is called in an invalid state
*/
public void setDataSource(FileDescriptor fd, long offset, long length)
throws IOException, IllegalArgumentException, IllegalStateException {
disableProxyListener();
_setDataSource(fd, offset, length);
}
private native void _setDataSource(FileDescriptor fd, long offset, long length)
throws IOException, IllegalArgumentException, IllegalStateException;
_setDataSource有native修饰，是libmedia_jni.so中的方法，找到 ./frameworks/base/media/jni/android_media_MediaPlayer.cpp
// ----------------------------------------------------------------------------
static JNINativeMethod gMethods[] = {
{
"_setDataSource",
"(Ljava/lang/String;[Ljava/lang/String;[Ljava/lang/String;)V",
(void *)android_media_MediaPlayer_setDataSourceAndHeaders
},
{"_setDataSource", "(Ljava/io/FileDescriptor;JJ)V", (void *)android_media_MediaPlayer_setDataSourceFD},
{"_setVideoSurface", "(Landroid/view/Surface;)V", (void *)android_media_MediaPlayer_setVideoSurface},
{"prepare", "()V", (void *)android_media_MediaPlayer_prepare},
{"prepareAsync", "()V", (void *)android_media_MediaPlayer_prepareAsync},
{"_start", "()V", (void *)android_media_MediaPlayer_start},
{"_stop", "()V", (void *)android_media_MediaPlayer_stop},
{"getVideoWidth", "()I", (void *)android_media_MediaPlayer_getVideoWidth},
{"getVideoHeight", "()I", (void *)android_media_MediaPlayer_getVideoHeight},
{"seekTo", "(I)V", (void *)android_media_MediaPlayer_seekTo},
{"_pause", "()V", (void *)android_media_MediaPlayer_pause},
{"isPlaying", "()Z", (void *)android_media_MediaPlayer_isPlaying},
{"getCurrentPosition", "()I", (void *)android_media_MediaPlayer_getCurrentPosition},
{"getDuration", "()I", (void *)android_media_MediaPlayer_getDuration},
{"_release", "()V", (void *)android_media_MediaPlayer_release},
{"_reset", "()V", (void *)android_media_MediaPlayer_reset},
{"setAudioStreamType", "(I)V", (void *)android_media_MediaPlayer_setAudioStreamType},
{"setLooping", "(Z)V", (void *)android_media_MediaPlayer_setLooping},
{"isLooping", "()Z", (void *)android_media_MediaPlayer_isLooping},
{"setVolume", "(FF)V", (void *)android_media_MediaPlayer_setVolume},
{"native_invoke", "(Landroid/os/Parcel;Landroid/os/Parcel;)I",(void *)android_media_MediaPlayer_invoke},
{"native_setMetadataFilter", "(Landroid/os/Parcel;)I", (void *)android_media_MediaPlayer_setMetadataFilter},
{"native_getMetadata", "(ZZLandroid/os/Parcel;)Z", (void *)android_media_MediaPlayer_getMetadata},
{"native_init", "()V", (void *)android_media_MediaPlayer_native_init},
{"native_setup", "(Ljava/lang/Object;)V", (void *)android_media_MediaPlayer_native_setup},
{"native_finalize", "()V", (void *)android_media_MediaPlayer_native_finalize},
{"getAudioSessionId", "()I", (void *)android_media_MediaPlayer_get_audio_session_id},
{"setAudioSessionId", "(I)V", (void *)android_media_MediaPlayer_set_audio_session_id},
{"setAuxEffectSendLevel", "(F)V", (void *)android_media_MediaPlayer_setAuxEffectSendLevel},
{"attachAuxEffect", "(I)V", (void *)android_media_MediaPlayer_attachAuxEffect},
{"native_pullBatteryData", "(Landroid/os/Parcel;)I", (void *)android_media_MediaPlayer_pullBatteryData},
{"setParameter", "(ILandroid/os/Parcel;)Z", (void *)android_media_MediaPlayer_setParameter},
{"getParameter", "(ILandroid/os/Parcel;)V", (void *)android_media_MediaPlayer_getParameter},
{"native_setRetransmitEndpoint", "(Ljava/lang/String;I)I", (void *)android_media_MediaPlayer_setRetransmitEndpoint},
{"setNextMediaPlayer", "(Landroid/media/MediaPlayer;)V", (void *)android_media_MediaPlayer_setNextMediaPlayer},
{"updateProxyConfig", "(Landroid/net/ProxyProperties;)V", (void *)android_media_MediaPlayer_updateProxyConfig},
};会进入如下函数
static void
android_media_MediaPlayer_setDataSourceFD(JNIEnv *env, jobject thiz, jobject fileDescriptor, jlong offset, jlong length)
{
sp<MediaPlayer> mp = getMediaPlayer(env, thiz);
if (mp == NULL ) {
jniThrowException(env, "java/lang/IllegalStateException", NULL);
return;
}
if (fileDescriptor == NULL) {
jniThrowException(env, "java/lang/IllegalArgumentException", NULL);
return;
}
int fd = jniGetFDFromFileDescriptor(env, fileDescriptor);
ALOGV("setDataSourceFD: fd %d", fd);
process_media_player_call( env, thiz, mp->setDataSource(fd, offset, length), "java/io/IOException", "setDataSourceFD failed." );
}mp->setDataSource(fd, offset, length) //调用打开文件方法
打开 ./frameworks/av/media/libmedia/mediaplayer.cpp setDataSource有三个重载函数，根据参数
status_t MediaPlayer::setDataSource(int fd, int64_t offset, int64_t length)
{
ALOGV("setDataSource(%d, %lld, %lld)", fd, offset, length);
status_t err = UNKNOWN_ERROR;
const sp<IMediaPlayerService>& service(getMediaPlayerService());
if (service != 0) {
sp<IMediaPlayer> player(service->create(this, mAudioSessionId));
if ((NO_ERROR != doSetRetransmitEndpoint(player)) ||
(NO_ERROR != player->setDataSource(fd, offset, length))) {
player.clear();
}
err = attachNewPlayer(player);
}
return err;
}打开 ./frameworks/av/media/libmedia/IMediaPlayer.cpp setDataSource也有三个重载函数，根据参数
status_t setDataSource(int fd, int64_t offset, int64_t length) {
Parcel data, reply;
data.writeInterfaceToken(IMediaPlayer::getInterfaceDescriptor());
data.writeFileDescriptor(fd);
data.writeInt64(offset);
data.writeInt64(length);
remote()->transact(SET_DATA_SOURCE_FD, data, &reply);
return reply.readInt32();
}这个打开文件流程只要是针对本地媒体文件。process_media_player_call( env, thiz, mp->setDataSource(fd, offset, length), "java/io/IOException", "setDataSourceFD failed." ) //根据返回的结果处理
// If exception is NULL and opStatus is not OK, this method sends an error
// event to the client application; otherwise, if exception is not NULL and
// opStatus is not OK, this method throws the given exception to the client
// application.
static void process_media_player_call(JNIEnv *env, jobject thiz, status_t opStatus, const char* exception, const char *message)
{
if (exception == NULL) { // Don't throw exception. Instead, send an event.
if (opStatus != (status_t) OK) {
sp<MediaPlayer> mp = getMediaPlayer(env, thiz);
if (mp != 0) mp->notify(MEDIA_ERROR, opStatus, 0);
}
} else { // Throw exception!
if ( opStatus == (status_t) INVALID_OPERATION ) {
jniThrowException(env, "java/lang/IllegalStateException", NULL);
} else if ( opStatus == (status_t) PERMISSION_DENIED ) {
jniThrowException(env, "java/lang/SecurityException", NULL);
} else if ( opStatus != (status_t) OK ) {
if (strlen(message) > 230) {
// if the message is too long, don't bother displaying the status code
jniThrowException( env, exception, message);
} else {
char msg[256];
// append the status code to the message
sprintf(msg, "%s: status=0x%X", message, opStatus);
jniThrowException( env, exception, msg);
}
}
}
}其它功能（start‘stop‘play‘seek_to）的流程也差不多，难点就是JNI技术和APP中的AIDL，当然以上只是一个简单的调用过程，要更深入了解还是要花些时间的。Android源码分析之Framework的MediaPlayer
原文地址：http://blog.csdn.net/deng0zhaotai/article/details/40076865
