1.1. MediaPlayer 播放流程
1.1.1. 1.MediaPlayer播放简介
从java层的Mediaplayer，通过JNI进行binder 连接到 mediaserver进程的 MediaPlayerService。MediaPlayerService中会根据传入的source，判断不同的播放器。
1.1 MediaPlayer基本框架
Java层
frameworks/base/media/java/android/media/MediaPlayer.java
JNI层 编译为 libmedia_jni.so
frameworks/base/media/jni/android_media_MediaPlayer.cpp
Native层 编译为 libmedia.so
frameworks/av/media/libmedia/mediaplayer.cpp
Binder 编译为 libmedia.so
frameworks/av/media/libmedia/IMediaPlayer.cpp
frameworks/av/media/libmedia/IMediaPlayerService.cpp
播放器 编译为 libmediaplayerservice.so
frameworks/av/media/libmediaplayerservice/nuplayer/NuPlayer.cpp
Binder可分为实名binder和匿名binder， 实名binder是在ServiceManager注册的servce，可以通过ServiceManager的getService获取，而匿名binder没在ServiceManager中注册，没法通过ServiceManager获取，需要想办法获取service的binder实例才能通讯。
对于MediaPlayer的结构，MediaPlayerServcie 属于实名binder， IMediaPlayer 和 IMediaPlayerClient 属于匿名binder。MediaPlayer 通过 MediaPlayerServcie实名binder， 将IMediaPlayerClient binder 传递给MediaPlayerServcie，同时MediaPlayerServcie将IMediaPlayer binder返回MediaPlayer。 这样MediaPlayer 就能通过 IMediaPlayer 调用 MediaPlayerServcie::client接口， MediaPlayerServcie可以通过IMediaPlayerClient调用MediaPlayer接口
1.2 MediaPlayer使用
这里主要分析setDataSource 、prepare、start
MediaPlayer = new MediaPlayer();
player.setDataSource(path);//*文件路径可以是*uri*，或者本地路径*
player.setAudioStreamType(AudioManager.STREAM_MUSIC); //*设置流类型*
player.prepare(); //*调用*prepare*方法*
player.start();//*调用*start*开始播放
1.1.2. 2.代码流程
2.1 setDataSource流程
- 从java层MediaPlayer.java，通过JNI调用到native层的mediaplayer.cpp
- native层通过IMediaPlayerService binder调用，返回mediaserver进程中 MediaPlayerService中的client对象
- MediaPlayerService中client，根据datasource类型创建对应播放器，一般为Nuplayer
frameworks/base/media/java/android/media/MediaPlayer.java
public void setDataSource(FileDescriptor fd, long offset, long length)
throws IOException, IllegalArgumentException, IllegalStateException {
_setDataSource(fd, offset, length);
}
private native void _setDataSource(FileDescriptor fd, long offset, long length)
throws IOException, IllegalArgumentException, IllegalStateException;
frameworks/base/media/jni/android_media_MediaPlayer.cpp
static void
android_media_MediaPlayer_setDataSourceFD(JNIEnv *env, jobject thiz, jobject fileDescriptor, jlong offset, jlong length)
{
sp<MediaPlayer> mp = getMediaPlayer(env, thiz);
//调用native层MediaPlayer实例mp的setdatasource，process_media_player_call负责抛出异常和错误
process_media_player_call( env, thiz, mp->setDataSource(fd, offset, length), "java/io/IOException", "setDataSourceFD failed." );
}
frameworks/av/media/libmedia/mediaplayer.cpp
status_t MediaPlayer::setDataSource(int fd, int64_t offset, int64_t length){
const sp<IMediaPlayerService> service(getMediaPlayerService());
if (service != 0) {
//调用mps的create方法，创建一个IMediaPlayer实例，作为应用端的mediaplayer跟mediaserver进程间的跨进程通信桥梁。
//IMediaPlayer对应服务端的实现是mediaplayerservice.cpp的内部类Client
sp<IMediaPlayer> player(service->create(this, mAudioSessionId)); //create操作
player->setDataSource(fd, offset, length);
err = attachNewPlayer(player);//保存这个MediaPlayerService:client
}
return err;
}
frameworks/av/media/libmedia/IMediaPlayerService.cpp
先看create()操作
位于IMediaPlayerService.cpp 中，可以看出是binder关系，对应的BnMediaPlayerService被MediaPlayerService继承实现
frameworks/av/media/libmediaplayerservice/MediaPlayerService.h
class MediaPlayerService : public BnMediaPlayerService{
生成一个client对象并返回，client继承于BnMediaPlayer，BnMediaPlayer是IMediaPlayer的接口
sp<IMediaPlayer> MediaPlayerService::create(const sp<IMediaPlayerClient>& client,
audio_session_t audioSessionId){
sp<Client> c = new Client(
this, pid, connId, client, audioSessionId,
IPCThreadState::self()->getCallingUid());
return c;
}
接下来再看player->setDataSource(fd, offset, length)，
通过传入参数判断playerType，具体在MediaPlayerService::Client中
status_t MediaPlayerService::Client::setDataSource(int fd, int64_t offset, int64_t length){
player_type playerType = MediaPlayerFactory::getPlayerType(this,fd,offset,length);//判断播放器类型
sp<MediaPlayerBase> p = setDataSource_pre(playerType);//预处理
// now set data source
return mStatus = setDataSource_post(p, p->setDataSource(fd, offset, length));//判断status状态 如果ok mPlayer = p;
}
setDataSource_pre 首先根据播放类型创建播放器，并创建AudioOutput对象。
sp<MediaPlayerBase> MediaPlayerService::Client::setDataSource_pre(player_type playerType){
sp<MediaPlayerBase> p = createPlayer(playerType);// 最终new NuPlayerDriver
if (!p->hardwareOutput()) {
mAudioOutput = new AudioOutput(mAudioSessionId, IPCThreadState::self()->getCallingUid(),
mPid, mAudioAttributes);
static_cast<MediaPlayerInterface*>(p.get())->setAudioSink(mAudioOutput);
}
return p;
}
NuPlayerDriver 的 setDataSource() mPlayer是 NuPlayer
frameworks/av/media/libmediaplayerservice/nuplayer/NuPlayerDriver.cpp
status_t NuPlayerDriver::setDataSource(int fd, int64_t offset, int64_t length) {
mPlayer->setDataSourceAsync(fd, offset, length); //NuPlayer
return mAsyncResult;
}
setDataSourceAsync中根据不同情况初始化了source的类型
frameworks/av/media/libmediaplayerservice/nuplayer/NuPlayer.cpp
void NuPlayer::setDataSourceAsync(
const sp<IMediaHTTPService> &httpService,
const char *url,
const KeyedVector<String8, String8> *headers) {
sp<AMessage> msg = new AMessage(kWhatSetDataSource, this);
size_t len = strlen(url);
sp<AMessage> notify = new AMessage(kWhatSourceNotify, this);
sp<Source> source;
if (IsHTTPLiveURL(url)) {
source = new HTTPLiveSource(notify, httpService, url, headers);
} else if (!strncasecmp(url, "rtsp://", 7)) {
source = new RTSPSource(
notify, httpService, url, headers, mUIDValid, mUID);
} else if ((!strncasecmp(url, "http://", 7)
|| !strncasecmp(url, "https://", 8))
&& ((len >= 4 && !strcasecmp(".sdp", &url[len - 4]))
|| strstr(url, ".sdp?"))) {
source = new RTSPSource(
notify, httpService, url, headers, mUIDValid, mUID, true);
} else {
sp<GenericSource> genericSource =
new GenericSource(notify, mUIDValid, mUID);
// Don't set FLAG_SECURE on mSourceFlags here for widevine.
// The correct flags will be updated in Source::kWhatFlagsChanged
// handler when GenericSource is prepared.
status_t err = genericSource->setDataSource(httpService, url, headers);
if (err == OK) {
source = genericSource;
} else {
ALOGE("Failed to set data source!");
}
}
msg->setObject("source", source);//这里的source 就是之后的mSource
msg->post();
}
留坑，解码相关
2.2 prepare()流程
frameworks/base/media/java/android/media/MediaPlayer.java
public void prepare() throws IOException, IllegalStateException {
_prepare();
scanInternalSubtitleTracks();
}
JNI
frameworks/base/media/jni/android_media_MediaPlayer.cpp
static voidandroid_media_MediaPlayer_prepare(JNIEnv *env, jobject thiz)
{
sp<MediaPlayer> mp = getMediaPlayer(env, thiz);
process_media_player_call( env, thiz, mp->prepare(), "java/io/IOException", "Prepare failed." );
}
frameworks/av/media/libmedia/mediaplayer.cpp
status_t MediaPlayer::prepare()
{
status_t ret = prepareAsync_l();
return mPrepareStatus;
}
status_t MediaPlayer::prepareAsync_l()
{
if ( (mPlayer != 0) && ( mCurrentState & (MEDIA_PLAYER_INITIALIZED | MEDIA_PLAYER_STOPPED) ) ) {
if (mAudioAttributesParcel != NULL) {
mPlayer->setParameter(KEY_PARAMETER_AUDIO_ATTRIBUTES, *mAudioAttributesParcel);
} else {
mPlayer->setAudioStreamType(mStreamType);
}
mCurrentState = MEDIA_PLAYER_PREPARING;
return mPlayer->prepareAsync(); // 对应IMediaPlayer.cpp
}
return INVALID_OPERATION;
}
frameworks/av/media/libmedia/IMediaPlayer.cpp
prepareAsync来到IMediaPlayer中，熟悉的binder，内部对应的BnMediaPlayer由 MediaPlayerService中的client实现
class Client : public BnMediaPlayer {
假设和上面一致，播放器p是 Nuplayer
status_t MediaPlayerService::Client::prepareAsync()
{
sp<MediaPlayerBase> p = getPlayer();
status_t ret = p->prepareAsync();
return ret;
}
frameworks/av/media/libmediaplayerservice/nuplayer/NuPlayer.cpp
void NuPlayer::prepareAsync() {
(new AMessage(kWhatPrepare, this))->post();
}
case kWhatPrepare:{
mSource->prepareAsync(); //这里的mSource是 取决于setDataSource时传入的。
break;
}
留坑 解码相关
2.3 start()流程
public void start() throws IllegalStateException {
baseStart(); //控制音量
stayAwake(true);//控制wakelock
_start();
}
private native void _start() throws IllegalStateException;
继续通过JNI来到
frameworks/av/media/libmedia/mediaplayer.cpp
这里的mPlayer,attachNewPlayer中传入的player对象，是IMediaPlayerService的service对象create()创建出来的,是一个MediaPlayerService:client对象，并在之后调用了setDataSource。 想不起来往上翻翻
status_t MediaPlayer::start()
{
} else if ( (mPlayer != 0) && ( mCurrentState & ( MEDIA_PLAYER_PREPARED |
MEDIA_PLAYER_PLAYBACK_COMPLETE | MEDIA_PLAYER_PAUSED ) ) ) {
mPlayer->setLooping(mLoop);
mPlayer->setVolume(mLeftVolume, mRightVolume);
mPlayer->setAuxEffectSendLevel(mSendLevel);
mCurrentState = MEDIA_PLAYER_STARTED;
ret = mPlayer->start();
}
}
frameworks/av/media/libmediaplayerservice/MediaPlayerService.cpp
status_t MediaPlayerService::Client::start()
{
sp<MediaPlayerBase> p = getPlayer(); //这里的p是 NuPlayerDriver
return p->start();
}
void NuPlayer::start() {
(new AMessage(kWhatStart, this))->post();
}
case kWhatStart:
{if (mStarted) {
// do not resume yet if the source is still buffering
if (!mPausedForBuffering) {
onResume(); //对应 mSource->resume();
}
} else {
onStart(); // 处理编解码 留坑
}
}