利用 android mediaRecorder c++类进行视频编码

来源：互联网发布：java 7年工作经验编辑：程序博客网时间：2024/06/09 15:47

本例中media source为camera。（学习的平台是android sdk6.0）

调用关系图：

startRecording：

1. recorder = New MediaRecorder(String16());

classMediaRecorder : public BnMediaRecorderClient,

public virtualIMediaDeathNotifier

a) 在创建mediaRecorder的时侯，我们先获取IMediaPlayerService指针，然后再创建IMediaRecorder

(关于的声明sp<IMediaRecorder> mMediaRecorder;)

mMediaRecorder =service->createMediaRecorder(opPackageName);

b) 在service->createMediaRecorder中会先把对象IMediaPlayerService序列话（利用data打包），然后把请求CREATE_MEDIA_RECORDER发送给remote（就是bpbinder）处理

remote()->transact(CREATE_MEDIA_RECORDER, data,&reply);

c) 最后根据远端的reply来创建本地对应的对象

interface_cast<IMediaRecorder>(reply.readStrongBinder());

2. 后续的方法都通过BpMediaRecorder（remote）来发送到BnMediaRecorder操作。

a) BnMediaRecorder继承了BnInterface<IMediaRecorder>，并实现了ontransact

classBnMediaRecorder: publicBnInterface<IMediaRecorder>

{

public:

virtual status_t onTransact( uint32_t code,

constParcel& data,

Parcel*reply,

uint32_tflags = 0);

};

b) 在这个方法里，每个操作都有对应的处理分支

c) BnMediaRecorder是个虚函数，具体工作由MediaRecorderClient来完成：MediaRecorderClient : public BnMediaRecorder

d) class BpMediaRecorder: public BpInterface<IMediaRecorder>

在对应的方法中最后都通过remote送给Bn处理，如：

Parceldata, reply;

data.writeInterfaceToken(IMediaRecorder::getInterfaceDescriptor());

data.writeString8(params);

remote()->transact(SET_PARAMETERS,data, &reply);

e) recorder->setParameters(…….)

f) recorder->prepare()

g) recorder->start()

3. 在MediaRecorderClient中封装了MediaRecorderBase这个类，每一项任务都要它来完成

在MediaRecorderClient的构造函数中可以看到

mRecorder = AVMediaServiceFactory::get()->createStagefrightRecorder(opPackageName);

a) 因此，具体的工作由StagefrightRecorder来完成

b) 在AVMediaServiceFactory.cpp中

StagefrightRecorder*AVMediaServiceFactory::createStagefrightRecorder(

const String16 &opPackageName) {

return newStagefrightRecorder(opPackageName);

}

4. StagefrightRecorder recorder->start（）

在prepare中或者start中调用StagefrightRecorder::prepareInternal()

在这里根据输出编码设定，选择对应的编码器进行初始化。

我们以OUTPUT_FORMAT_MPEG_4为例进行分析

根据输出格式进入setupMPEG4orWEBMRecording()

5. setupMPEG4orWEBMRecording()

在这里创建了MPEG4Writer

a) writer = mp4writer =AVFactory::get()->CreateMPEG4Writer(mOutputFd);

b) setupMediaSource将camera指定为encoder的input source

c) sp<MediaSource> encoder;

err = setupVideoEncoder(mediaSource, &encoder);创建encoder

d) setupVideoEncoder(mediaSource,&encoder);

首先将camera中的各项参数设定读出来设入到encoder中（camera为null则使用default值）

sp<MetaData>meta = cameraSource->getFormat();

int32_t width, height, stride,sliceHeight, colorFormat;

CHECK(meta->findInt32(kKeyWidth,&width));

CHECK(meta->findInt32(kKeyHeight,&height));

CHECK(meta->findInt32(kKeyStride,&stride));

CHECK(meta->findInt32(kKeySliceHeight, &sliceHeight));

CHECK(meta->findInt32(kKeyColorFormat, &colorFormat));

format->setInt32("width",width);

format->setInt32("height",height);

format->setInt32("stride",stride);

format->setInt32("slice-height", sliceHeight);

format->setInt32("color-format", colorFormat);

这里预留了custom参数设置函数，android中默认没有实现，是空函数

接着创建encoder。

sp<MediaCodecSource> encoder =MediaCodecSource::Create(

mLooper, format, cameraSource,mPersistentSurface, flags);

e) sp<MediaCodecSource> encoder

=MediaCodecSource::Create(

mLooper,

format,

cameraSource,

mPersistentSurface,

flags);

在create函数中先new一个对象，

sp<MediaCodecSource> mediaSource =

new MediaCodecSource(looper, format, source, consumer, flags);

if (mediaSource->init() == OK) {

return mediaSource;

}

f) MediaCodecSource::init()

status_t err = initEncoder();

g) initEncoder()｛

mReflector = new AHandlerReflector<MediaCodecSource>(this);

mLooper->registerHandler(mReflector);

mCodecLooper = new ALooper;

mCodecLooper->setName("codec_looper");

mCodecLooper->start();

……………..

mEncoder =MediaCodec::CreateByType(

mCodecLooper,outputMIME.c_str(), true /* encoder */);

….

mEncoderActivityNotify =new AMessage(kWhatEncoderActivity, mReflector);

mEncoder->setCallback(mEncoderActivityNotify);

status_t err =mEncoder->configure(

mOutputFormat,

NULL /*nativeWindow */,

NULL /* crypto*/,

MediaCodec::CONFIGURE_FLAG_ENCODE);

…………………………

err = mEncoder->start();

｝

h) MediaCodec::CreateByType(

mCodecLooper, outputMIME.c_str(), true /* encoder */) {

sp<MediaCodec> codec = new MediaCodec(looper, pid);

const status_tret = codec->init(mime, true /* nameIsType */, encoder);

}

i) MediaCodec::init (const AString&name, bool nameIsType, bool encoder) {

………..

/// name 包含video, nameIsType is true

因此

mCodec =AVFactory::get()->createACodec();

…………..

mIsVideo =true;

…………..

mCodecLooper->registerHandler(mCodec);

mCodec->setNotificationMessage(newAMessage(kWhatCodecNotify, this));

sp<AMessage> msg = newAMessage(kWhatInit, this);

msg->setString("name", name);

msg->setInt32("nameIsType",nameIsType);

if (nameIsType) {

msg->setInt32("encoder",encoder);

}

status_t err;

Vector<MediaResource> resources;

const char *type = secureCodec ?kResourceSecureCodec : kResourceNonSecureCodec;

const char *subtype = mIsVideo ?kResourceVideoCodec : kResourceAudioCodec;

resources.push_back(MediaResource(String8(type), String8(subtype), 1));

for (int i = 0; i <= kMaxRetry; ++i) {

if (i > 0) {

// Don't try to reclaim resourcefor the first time.

if(!mResourceManagerService->reclaimResource(resources)) {

break;

}

sp<AMessage> response;

err = PostAndAwaitResponse(msg,&response);

if (!isResourceError(err)) {

break;

}

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