利用 android mediaRecorder c++类进行视频编码 _视频编码

青春须早为，岂能长少年。这篇文章主要讲述利用 android mediaRecorder c++类进行视频编码相关的知识，希望能为你提供帮助。
本例中media source为camera。（学习的平台是android sdk6.0）
调用关系图：

startRecording：

recorder = New MediaRecorder(String16());

classMediaRecorder : public BnMediaRecorderClient,
public virtualIMediaDeathNotifier

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);

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);

最后根据远端的reply来创建本地对应的对象

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

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);
};

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
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);

recorder-> setParameters(…….)
recorder-> prepare()
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);

因此，具体的工作由StagefrightRecorder来完成
在AVMediaServiceFactory.cpp中

StagefrightRecorder*AVMediaServiceFactory::createStagefrightRecorder(
const String16 & opPackageName) {
return newStagefrightRecorder(opPackageName);
}

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()

setupMPEG4orWEBMRecording()

在这里创建了MPEG4Writer

writer = mp4writer =AVFactory::get()-> CreateMPEG4Writer(mOutputFd);
setupMediaSource将camera指定为encoder的input source
sp< MediaSource> encoder;

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

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);

sp< MediaCodecSource> encoder

=MediaCodecSource::Create(
mLooper,
format,
cameraSource,
mPersistentSurface,

;

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;
}

MediaCodecSource::init()

status_t err = initEncoder();

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();
｝

MediaCodec::CreateByType(

mCodecLooper, outputMIME.c_str(), true /* encoder */) {
sp< MediaCodec> codec = new MediaCodec(looper, pid);

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

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;
}
}
}

【利用 android mediaRecorder c++类进行视频编码】本文出自 “龙骑舞” 博客，请务必保留此出处http://westfisher.blog.51cto.com/3396434/1945121