应用场景:
MediaPlayer mediaPlayer = new MediaPlayer(); mediaPlayer.setOnCompletionListener(new OnCompletionListener() { @Override public void onCompletion(MediaPlayer mp) { mediaPlayer.release(); mediaPlayer = null; } }); mediaPlayer.setDataSource(“abc.mp3”); mediaPlayer.prepare(); mediaPlayer.start();
一、setDataSource
在MediaPlayer.java 中public void setDataSource(FileDescriptor fd, long offset, long length) throws IOException, IllegalArgumentException, IllegalStateException { disableProxyListener(); setDataSource(fd, offset, length); }
setDataSource终于调用了native函数:_setDataSource(fd,offset, length);
我们直接跳到JNI层来看它的详细实现
依据JNI相关的知识,在android_media_MediaPlayer.cpp中找到了事实上现代码: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为MediaPlayer类型的对象,在JNI层创建,在MediaPlayer.cpp中。一起来看setDataSource的实现。
status_t MediaPlayer::setDataSource(int fd, int64_t offset, int64_t 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; }
getMediaPlayerService()为一个典型的Binder机制向ServiceManager获取服务的方法,Binder这方面的知识能够參考http://blog.csdn.net/super_dc/article/details/37738123和http://blog.csdn.net/super_dc/article/details/37764947
service->create(this, mAudioSessionId),先看create方法在IMediaPlayerService.cpp中的实现:virtual sp<IMediaPlayer> create( const sp<IMediaPlayerClient>& client, int audioSessionId) { Parcel data, reply; data.writeInterfaceToken(IMediaPlayerService::getInterfaceDescriptor()); data.writeStrongBinder(client->asBinder()); data.writeInt32(audioSessionId); remote()->transact(CREATE, data, &reply); return interface_cast<IMediaPlayer>(reply.readStrongBinder()); }这里仅仅是Binder客户端的实现。其终于实现会在MediaPlayerService.cpp中由服务端MediaPlayerService来实现。
sp<IMediaPlayer> MediaPlayerService::create(const sp<IMediaPlayerClient>& client, int audioSessionId) { pid_t pid = IPCThreadState::self()->getCallingPid(); int32_t connId = android_atomic_inc(&mNextConnId); sp<Client> c = new Client( this, pid, connId, client, audioSessionId, IPCThreadState::self()->getCallingUid()); ALOGV("Create new client(%d) from pid %d, uid %d, ", connId, pid, IPCThreadState::self()->getCallingUid()); /* add by Gary. start {{----------------------------------- */ c->setScreen(mScreen); /* add by Gary. end -----------------------------------}} */ c->setSubGate(mGlobalSubGate); // 2012-03-12, add the global interfaces to control the subtitle gate wp<Client> w = c; { Mutex::Autolock lock(mLock); mClients.add(w); } return c; }
综合上面两点,sp<IMediaPlayer>player(service->create(this, mAudioSessionId));中player实际上是一个Client类型对象的proxy。
其详细实现都在Client中实现。
player->setDataSource(fd, offset, length)就能够直接到MediaPlayerService.cpp中的Client类中来看其详细实现了。status_t MediaPlayerService::Client::setDataSource(int fd, int64_t offset, int64_t length) { struct stat sb; int ret = fstat(fd, &sb); if (ret != 0) { ALOGE("fstat(%d) failed: %d, %s", fd, ret, strerror(errno)); return UNKNOWN_ERROR; } if (offset >= sb.st_size) { ALOGE("offset error"); ::close(fd); return UNKNOWN_ERROR; } if (offset + length > sb.st_size) { length = sb.st_size - offset; ALOGV("calculated length = %lld", length); } // 关键点1 player_type playerType = MediaPlayerFactory::getPlayerType(this, fd, offset, length); // 关键点2 sp<MediaPlayerBase> p = setDataSource_pre(playerType); if (p == NULL) { return NO_INIT; } // now set data source // 关键点3 setDataSource_post(p, p->setDataSource(fd, offset, length)); return mStatus; }这里有3个关键点。我们分别破解之,先看getPlayerType
player_type MediaPlayerFactory::getPlayerType(const sp<IMediaPlayer>& client, int fd, int64_t offset, int64_t length) { GET_PLAYER_TYPE_IMPL(client, fd, offset, length); } #define GET_PLAYER_TYPE_IMPL(a...) \ Mutex::Autolock lock_(&sLock); \ \ player_type ret = STAGEFRIGHT_PLAYER; \ float bestScore = 0.0; \ \ for (size_t i = 0; i < sFactoryMap.size(); ++i) { \ \ IFactory* v = sFactoryMap.valueAt(i); \ float thisScore; \ CHECK(v != NULL); \ thisScore = v->scoreFactory(a, bestScore); \ if (thisScore > bestScore) { \ ret = sFactoryMap.keyAt(i); \ bestScore = thisScore; \ } \ } \ \ if (0.0 == bestScore) { \ ret = getDefaultPlayerType(); \ } \ \ return ret;
MediaPlayerFactory作为一个工厂类,各种mediaplayer向它注冊。并各自实现scoreFactory和createPlayer用来推断当前多媒体文件是否适合用此mediaplayer来播放和创建mediaplayer。在哪儿注冊mediaplayer呢?在MediaPlayerService的构造函数中,也就是说当向系统注冊MediaPlayerService服务时,就已经注冊了一些mediaplayer了。
播放mp3文件时。会创建STAGEFRIGHT_PLAYER,这也是默认的播放器。
以下就以STAGEFRIGHT_PLAYER来继续以下的流程。
到眼下为止,我们知道playerType返回了STAGEFRIGHT_PLAYER。接着来看关键点2.sp<MediaPlayerBase> MediaPlayerService::Client::setDataSource_pre( player_type playerType) { ALOGV("player type = %d", playerType); // create the right type of player sp<MediaPlayerBase> p = createPlayer(playerType); if (p == NULL) { return p; } if (!p->hardwareOutput()) { mAudioOutput = new AudioOutput(mAudioSessionId); static_cast<MediaPlayerInterface*>(p.get())->setAudioSink(mAudioOutput); } return p; }
依据playerType创建播放器,实际上就是创建StagefrightPlayer
再看关键点3,p->setDataSource(fd,offset, length)实际上就是调用了StagefrightPlayer的setDataSource。看代码:
StagefrightPlayer::StagefrightPlayer() : mPlayer(new AwesomePlayer) { ALOGV("StagefrightPlayer"); mPlayer->setListener(this); } status_t StagefrightPlayer::setDataSource(int fd, int64_t offset, int64_t length) { ALOGV("setDataSource(%d, %lld, %lld)", fd, offset, length); return mPlayer->setDataSource(dup(fd), offset, length); }由代码可知。StagefrightPlayer仅仅是AwesomePlayer的代理类,详细实现还在AwesomePlayer里面。
status_t AwesomePlayer::setDataSource( int fd, int64_t offset, int64_t length) { Mutex::Autolock autoLock(mLock); reset_l(); sp<DataSource> dataSource = new FileSource(fd, offset, length); status_t err = dataSource->initCheck(); if (err != OK) { return err; } mFileSource = dataSource; { Mutex::Autolock autoLock(mStatsLock); mStats.mFd = fd; mStats.mURI = String8(); } return setDataSource_l(dataSource); }FileSource类实现了数据读取,播放器调用dataSource->readAt来获取数据,另外,其基类DataSource提供了一些分离器例如以下。
RegisterDefaultSniffers将在AwesomePlayer的构造函数中被调用。
// static void DataSource::RegisterDefaultSniffers() { RegisterSniffer(SniffMPEG4); RegisterSniffer(SniffMatroska); RegisterSniffer(SniffOgg); RegisterSniffer(SniffWAV); RegisterSniffer(SniffFLAC); RegisterSniffer(SniffAMR); RegisterSniffer(SniffMPEG2TS); RegisterSniffer(SniffMP3); RegisterSniffer(SniffAAC); RegisterSniffer(SniffMPEG2PS); RegisterSniffer(SniffWVM); char value[PROPERTY_VALUE_MAX]; if (property_get("drm.service.enabled", value, NULL) && (!strcmp(value, "1") || !strcasecmp(value, "true"))) { RegisterSniffer(SniffDRM); } }接着往下看setDataSource_l(dataSource)
status_t AwesomePlayer::setDataSource_l( const sp<DataSource> &dataSource) { // 对于不同的文件格式会创建不同的MediaExtractor。MP3文件会创建MP3Extractor // 文件格式靠source->sniff(&tmp, &confidence, &meta)来区分。这个函数会遍历之前通过RegisterSniffer注冊的分离器,得到最合适的文件格式 sp<MediaExtractor> extractor = MediaExtractor::Create(dataSource); if (extractor == NULL) { return UNKNOWN_ERROR; } if (extractor->getDrmFlag()) { checkDrmStatus(dataSource); } return setDataSource_l(extractor); } status_t AwesomePlayer::setDataSource_l(const sp<MediaExtractor> &extractor) { // Attempt to approximate overall stream bitrate by summing all // tracks\' individual bitrates, if not all of them advertise bitrate, // we have to fail. int64_t totalBitRate = 0; mExtractor = extractor; for (size_t i = 0; i < extractor->countTracks(); ++i) { sp<MetaData> meta = extractor->getTrackMetaData(i); int32_t bitrate; if (!meta->findInt32(kKeyBitRate, &bitrate)) { const char *mime; CHECK(meta->findCString(kKeyMIMEType, &mime)); ALOGV("track of type \'%s\' does not publish bitrate", mime); totalBitRate = -1; break; } totalBitRate += bitrate; } mBitrate = totalBitRate; ALOGV("mBitrate = %lld bits/sec", mBitrate); { Mutex::Autolock autoLock(mStatsLock); mStats.mBitrate = mBitrate; mStats.mTracks.clear(); mStats.mAudioTrackIndex = -1; mStats.mVideoTrackIndex = -1; } bool haveAudio = false; bool haveVideo = false; for (size_t i = 0; i < extractor->countTracks(); ++i) { sp<MetaData> meta = extractor->getTrackMetaData(i); const char *_mime; CHECK(meta->findCString(kKeyMIMEType, &_mime)); String8 mime = String8(_mime); if (!haveVideo && !strncasecmp(mime.string(), "video/", 6)) { setVideoSource(extractor->getTrack(i)); haveVideo = true; // Set the presentation/display size int32_t displayWidth, displayHeight; bool success = meta->findInt32(kKeyDisplayWidth, &displayWidth); if (success) { success = meta->findInt32(kKeyDisplayHeight, &displayHeight); } if (success) { mDisplayWidth = displayWidth; mDisplayHeight = displayHeight; } { Mutex::Autolock autoLock(mStatsLock); mStats.mVideoTrackIndex = mStats.mTracks.size(); mStats.mTracks.push(); TrackStat *stat = &mStats.mTracks.editItemAt(mStats.mVideoTrackIndex); stat->mMIME = mime.string(); } } else if (!haveAudio && !strncasecmp(mime.string(), "audio/", 6)) { setAudioSource(extractor->getTrack(i)); haveAudio = true; mActiveAudioTrackIndex = i; { Mutex::Autolock autoLock(mStatsLock); mStats.mAudioTrackIndex = mStats.mTracks.size(); mStats.mTracks.push(); TrackStat *stat = &mStats.mTracks.editItemAt(mStats.mAudioTrackIndex); stat->mMIME = mime.string(); } if (!strcasecmp(mime.string(), MEDIA_MIMETYPE_AUDIO_VORBIS)) { // Only do this for vorbis audio, none of the other audio // formats even support this ringtone specific hack and // retrieving the metadata on some extractors may turn out // to be very expensive. sp<MetaData> fileMeta = extractor->getMetaData(); int32_t loop; if (fileMeta != NULL && fileMeta->findInt32(kKeyAutoLoop, &loop) && loop != 0) { modifyFlags(AUTO_LOOPING, SET); } } } else if (!strcasecmp(mime.string(), MEDIA_MIMETYPE_TEXT_3GPP)) { addTextSource_l(i, extractor->getTrack(i)); } } if (!haveAudio && !haveVideo) { if (mWVMExtractor != NULL) { return mWVMExtractor->getError(); } else { return UNKNOWN_ERROR; } } mExtractorFlags = extractor->flags(); return OK; }MediaExtractor涉及到媒体文件格式的非常多内容,比方track的构成。有几种track等等。后面再做解说,这里我们播放的是MP3文件,所以countTracks的值为1。sp<MetaData> meta = extractor->getTrackMetaData(i)中meta的kKeyMIMEType值为"audio/",将会运行到setAudioSource(extractor->getTrack(i)),再看代码:
sp<MediaSource> MP3Extractor::getTrack(size_t index) { if (mInitCheck != OK || index != 0) { return NULL; } // 返回的是一个MP3Source对象 return new MP3Source( mMeta, mDataSource, mFirstFramePos, mFixedHeader, mSeeker); } void AwesomePlayer::setAudioSource(sp<MediaSource> source) { CHECK(source != NULL); mAudioTrack = source; }至此,setdatasource就分析完毕,下一篇将分析prepare的实现过程。