video/audio playback：setDataSource

最新推荐文章于 2024-10-24 02:48:20 发布

转载最新推荐文章于 2024-10-24 02:48:20 发布 · 1k 阅读

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#playback #url #string #descriptor #file #service

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本文详细解析了Android平台上实现音视频播放的过程，包括MediaPlayer组件的使用、不同类型的音视频文件处理方式、以及如何通过Stagefright播放器进行HTTP流媒体播放。

实现video/audio playerback，需要经过如下步骤：

MediaPlayer mp = new MediaPlayer();

mp.setDataSource(String URL/FILE_PATH);

mp.prepare();

mp.start();

首先是setDataSource : 创建player, 如果url是以content://形式的转换为FD，并提取出mAudioTrack/mVideoTrack保存起来，如果url是以http://之类的在线播放多媒体信息，需去下载SDP文件，找到url存储起来

1.framework/base/media/libmedia/ MediaPlayer.cpp

status_t MediaPlayer::setDataSource(

const char *url, const KeyedVector<String8, String8> *headers) {

…

(1) const sp<IMediaPlayerService>& service(getMediaPlayerService()); ……首先获得mediaplayerService的服务

if (service != 0) {

（2） sp<IMediaPlayer> player(service->create(getpid(), this, fd, offset, length, mAudioSessionId));

（3） err = setDataSource(player);

}

return err;

}

2. framework/base/media/libmediaplayerservice/ MediaPlayerService.cpp

sp<IMediaPlayer> MediaPlayerService::create(

pid_t pid, const sp<IMediaPlayerClient>& client, const char* url,

const KeyedVector<String8, String8> *headers, int audioSessionId)

{

….

sp<Client> c = new Client(this, pid, connId, client, audioSessionId); …. 新建个mediaplayerservice client 的实例,即整个播放过程由这个实例控制

………

if (NO_ERROR != c->setDataSource(url, headers))…..create player 并setDataSource

{

c.clear();

return c;

}

status_t MediaPlayerService::Client::setDataSource(

const char *url, const KeyedVector<String8, String8> *headers)

{….

如果是url 以content://开头要转换为file descriptor

if (strncmp(url, "content://", 10) == 0) {…

int fd = android::openContentProviderFile(url16);

……….

setDataSource(fd, 0, 0x7fffffffffLL); // this sets mStatus

close(fd);

return mStatus;

} else {

player_type playerType = getPlayerType(url);…. createplayer前要判断是哪种类型

LOGV("player type = %d", playerType);

// create the right type of player

sp<MediaPlayerBase> p = createPlayer(playerType);

mStatus = p->setDataSource(url, headers);

…

return mStatus;

}

player_type getPlayerType(const char* url) ……………. 根据url的后缀名判断属于哪种playerType，默认是stagefright

{

if (TestPlayerStub::canBeUsed(url)) {

return TEST_PLAYER;

}

// use MidiFile for MIDI extensions

int lenURL = strlen(url);

for (int i = 0; i < NELEM(FILE_EXTS); ++i) {

int len = strlen(FILE_EXTS[i].extension);

int start = lenURL - len;

if (start > 0) {

if (!strncasecmp(url + start, FILE_EXTS[i].extension, len)) {

return FILE_EXTS[i].playertype;

}

……………….

return getDefaultPlayerType();

}

有如下类型的playerType：

typedef struct {

const char *extension;

const player_type playertype;

} extmap;

extmap FILE_EXTS [] = {

{".mid", SONIVOX_PLAYER},

{".midi", SONIVOX_PLAYER},

{".smf", SONIVOX_PLAYER},

{".xmf", SONIVOX_PLAYER},

{".mxmf", SONIVOX_PLAYER},

{".imy", SONIVOX_PLAYER},

{".rtttl", SONIVOX_PLAYER},

{".rtx", SONIVOX_PLAYER},

{".ota", SONIVOX_PLAYER},

{".mnv", SOLS_PLAYER},

{".mnvtmp", SOLS_PLAYER},

#ifndef NO_OPENCORE

{".wma", PV_PLAYER},

{".wmv", PV_PLAYER},

{".asf", PV_PLAYER},

#endif

};

sp<MediaPlayerBase> MediaPlayerService::Client::createPlayer(player_type playerType)

{……. if (p == NULL) {

p = android::createPlayer(playerType, this, notify);

}

return p;

}

static sp<MediaPlayerBase> createPlayer(player_type playerType, void* cookie,

notify_callback_f notifyFunc)

{

sp<MediaPlayerBase> p;

switch (playerType) {

#ifndef NO_OPENCORE

case PV_PLAYER:

LOGV(" create PVPlayer");

p = new PVPlayer();

break;

#endif

case SONIVOX_PLAYER:

LOGV(" create MidiFile");

p = new MidiFile();

break;

case STAGEFRIGHT_PLAYER:

LOGV(" create StagefrightPlayer");

p = new StagefrightPlayer;

break;

case TEST_PLAYER:

LOGV("Create Test Player stub");

p = new TestPlayerStub();

break;

case SOLS_PLAYER:

LOGV(" create SolsStagefrightPlayer");

p = new SolsStagefrightPlayer;

break;

}….

return p;

}

3, framework/base/media/libmediaplayerservice/ StagefrightPlayer.cpp

创建stagefrightplayer实例也new了个AwesomePlayer(mPlayer)

StagefrightPlayer::StagefrightPlayer()

: mPlayer(new AwesomePlayer) {

LOGV("StagefrightPlayer");

mPlayer->setListener(this);

}

4, framework/base/media/libStagefright/ AwesomePlayer.cpp

在AwesomePlayer setDataSource 根据传过来的是 url(http://..)，还是fd进行不同的处理

url：记录下url 和 http request header , mediaextract 在::finishSetDataSource_l 中进行。

status_t AwesomePlayer::setDataSource_l(

const char *uri, const KeyedVector<String8, String8> *headers) {

LOGV("setDataSource '%s'", uri);

// Check for sdp

status_t err;

if (headers) {

mUriHeaders = *headers;

}…….

if (extension.length() == 4 && !strncasecmp(extension.string(), ".sdp", 4)) {

//found sdp

if (!strncasecmp("http://", tmpString8Uri.string(), 7)) {

LOGV("found SDP file over http");

String8 newUri;

err = getUriFromSDP(uri, &newUri);…………..Download SDP, parse and return found URI SDP:Service Data Point业务数据点

if (err == OK) {

return setDataSource_l(newUri.string(), headers);

} else {

}

reset_l();

mUri = uri;

return OK;

}

FD 形式：根据FD 生成filesource ，后找到匹配的mediaextractor--->mVideoTrack/mAudioTrack

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);

…..

return setDataSource_l(dataSource);

}

status_t AwesomePlayer::setDataSource_l(

const sp<DataSource> &dataSource) {

sp<MediaExtractor> extractor = MediaExtractor::Create(dataSource);…….创建对应的extractor

…..

return setDataSource_l(extractor);

}

status_t AwesomePlayer::setDataSource_l(const sp<MediaExtractor> &extractor) {

…

if (!haveVideo && !strncasecmp(mime, "video/", 6)) {

setVideoSource(extractor->getTrack(i)); ………>mVideoTrack

haveVideo = true;

} else if (!haveAudio && !strncasecmp(mime, "audio/", 6)) {

setAudioSource(extractor->getTrack(i));……….>mAudioTrack

haveAudio = true;

return OK;

}

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