通过MediaRecorder源码学习系统源码定位

Posted 2022-11-25 楠之枫雪

找到加载的so库

public class MediaRecorder implements AudioRouting,
                                      AudioRecordingMonitor,
                                      AudioRecordingMonitorClient,
                                      MicrophoneDirection

    static 
        System.loadLibrary("media_jni");
        native_init();
    

定位到media_jni源码

media_jni的目录：
告诉你个规律吧！java文件的包名来找到它的JNI文件名。 比如mediaplayer.java 属于android.media.mediaplayer 包 那么JNI 文件就是android_media_mediaplayer.cpp 注意看包名和JNI文件名的对应关系 路径是framework\\media\\base\\jni\\

/frameworks/base/media/jni/android_media_MediaRecorder.cpp
然后上面这个类主要是调用/frameworks/av/media/libmedia/mediarecorder.cpp
需要注意一个问题，就是java的native方法名不一定和cpp文件里的一致

源码跟踪

• 我们要查找的是prepare方法，按照上面的规律是在android_media_MediaRecorder.cpp。找到定位到该方法

static void
android_media_MediaRecorder_prepare(JNIEnv *env, jobject thiz)

    ALOGV("prepare");
    sp<MediaRecorder> mr = getMediaRecorder(env, thiz);
    if (mr == NULL) 
        jniThrowException(env, "java/lang/IllegalStateException", NULL);
        return;
    

    jobject surface = env->GetObjectField(thiz, fields.surface);
    if (surface != NULL) 
        const sp<Surface> native_surface = get_surface(env, surface);

        // The application may misbehave and
        // the preview surface becomes unavailable
        if (native_surface.get() == 0) 
            ALOGE("Application lost the surface");
            jniThrowException(env, "java/io/IOException", "invalid preview surface");
            return;
        

        ALOGI("prepare: surface=%p", native_surface.get());
        if (process_media_recorder_call(env, mr->setPreviewSurface(native_surface->getIGraphicBufferProducer()), "java/lang/RuntimeException", "setPreviewSurface failed.")) 
            return;
        
    
    process_media_recorder_call(env, mr->prepare(), "java/io/IOException", "prepare failed.");

可以知道，这里调用到了MediaRecorder

• 搜索并打开MediaRecorder.cpp

status_t MediaRecorder::prepare()

    ALOGV("prepare");
    if (mMediaRecorder == NULL) 
        ALOGE("media recorder is not initialized yet");
        return INVALID_OPERATION;
    
    if (!(mCurrentState & MEDIA_RECORDER_DATASOURCE_CONFIGURED)) 
        ALOGE("prepare called in an invalid state: %d", mCurrentState);
        return INVALID_OPERATION;
    
    if (mIsAudiosourceSet != mIsAudioEncoderSet) 
        if (mIsAudioSourceSet) 
            ALOGE("audio source is set, but audio encoder is not set");
         else   // must not happen, since setAudioEncoder checks this already
            ALOGE("audio encoder is set, but audio source is not set");
        
        return INVALID_OPERATION;
    

    if (mIsVideoSourceSet != mIsVideoEncoderSet) 
        if (mIsVideoSourceSet) 
            ALOGE("video source is set, but video encoder is not set");
         else   // must not happen, since setVideoEncoder checks this already
            ALOGE("video encoder is set, but video source is not set");
        
        return INVALID_OPERATION;
    

    status_t ret = mMediaRecorder->prepare();
    if (OK != ret) 
        ALOGE("prepare failed: %d", ret);
        mCurrentState = MEDIA_RECORDER_ERROR;
        return ret;
    
    mCurrentState = MEDIA_RECORDER_PREPARED;
    return ret;

里面定位到了mMediaRecorder变量

• 通过头文件定位到mediarecorder.h

#include <media/mediarecorder.h>

• 在framew下搜索并打开该文件，找到该变量
  
• 明显是去到了IMediaRecorder，依旧在framework下搜索IMediaRecorder
  
  明显源码就在IMediaRecorder.cpp中

感谢参考：https://blog.51cto.com/u_4259297/2161337
感谢参考：https://blog.csdn.net/tq501501/article/details/117444705
转载注明：https://blog.csdn.net/u014614038/article/details/117731557