Android MediaRecorder.prepare（）是做什麼的？

Question

official Android documentation for MediaRecorder.prepare()說：

準備記錄器開始捕獲和編碼數據。在設置所需的音頻和視頻源，編碼器，文件格式等之後，但在啓動（）之前，必須調用此方法。

正是這樣做有什麼，爲什麼我們需要調用它之前，我們開始捕捉媒體數據？

Answer 1

該函數（prepare（））將創建一個隨機訪問文件流，以便從具有指定名稱的文件中讀取數據，並可選擇寫入文件。 這是流處理所必需的。除非使用此函數，否則流程將不會啓動。 see this doc.

Answer 2

您可能需要閱讀源代碼在這裏：MediaRecorder.java:833

代碼一瞥：

/** 
* Prepares the recorder to begin capturing and encoding data. This method 
* must be called after setting up the desired audio and video sources, 
* encoders, file format, etc., but before start(). 
* 
* @throws IllegalStateException if it is called after 
* start() or before setOutputFormat(). 
* @throws IOException if prepare fails otherwise. 
*/ 
public void prepare() throws IllegalStateException, IOException 
{ 
    if (mPath != null) { 
     RandomAccessFile file = new RandomAccessFile(mPath, "rws"); 
     try { 
      _setOutputFile(file.getFD(), 0, 0); 
     } finally { 
      file.close(); 
     } 
    } else if (mFd != null) { 
     _setOutputFile(mFd, 0, 0); 
    } else { 
     throw new IOException("No valid output file"); 
    } 

    _prepare(); 
} 

這裏的代碼的本地部分：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; 
}