added audio capturer usage doc

Signed-off-by: NGeevarghese V K <geevarghese.v.k1@huawei.com>

en/application-dev/media/audio-capturer.md

+# Audio Recorder Development Using AudioCapturer
+
+---
+## ***Note***:
+    1. This document applies to JavaScript.
+---
+## **Summary**
+This guide will show how a JS application can use AudioCapturer to record the audio.
+Applications can use the APIs provided in this document to record raw audio files.
+
+## **AudioCapturer Framework**
+The AudioCapturer interface is one of the most important components of the audio framework.
+### **Audio Capturing:**
+The AudioCapturer framework provides APIs for capturing raw audio files.
+
+## **Usage**
+Here's an example of how to use AudioCapturer to capture a raw audio file.
+1. Use **createAudioCapturer()** to create an AudioCapturer instance. Capturer parameters can be set in **audioCapturerOptions**.\
+   This instance can be used to record, control, and obtain the recording status, as well as to register a callback for notifications.
+   ```
+    var audioStreamInfo = {
+        samplingRate: audio.AudioSamplingRate.SAMPLE_RATE_44100,
+        channels: audio.AudioChannel.CHANNEL_1,
+        sampleFormat: audio.AudioSampleFormat.SAMPLE_FORMAT_S16LE,
+        encodingType: audio.AudioEncodingType.ENCODING_TYPE_RAW
+    }
+
+    var audioCapturerInfo = {
+        source: audio.SourceType.SOURCE_TYPE_MIC,
+        capturerFlags: 1
+    }
+
+    var audioCapturerOptions = {
+        streamInfo: audioStreamInfo,
+        capturerInfo: audioCapturerInfo
+    }
+
+    let audioCapturer = await audio.createAudioCapturer(audioCapturerOptions);
+    var state = audioRenderer.state;
+   ```
+
+2. (Optional) Subscribe to audio capturer state change events using the **on('stateChange')** API.
+   If an application wants to take some action based on the state updates in capturer, the application can subscribe to the state change event.
+   There are more events that applications can subscribe to, such as 'markReach' and 'periodReach'. Refer to [**js-apis-audio.md**](https://gitee.com/openharmony/docs/blob/master/en/application-dev/reference/apis/js-apis-audio.md) for more details.
+   ```
+    audioCapturer.on('stateChange',(state) => {
+    console.info('AudioCapturerLog: Changed State to : ' + state)
+    switch (state) {
+        case audio.AudioState.STATE_PREPARED:
+            console.info('--------CHANGE IN AUDIO STATE----------PREPARED--------------');
+            console.info('Audio State is : Prepared');
+            break;
+        case audio.AudioState.STATE_RUNNING:
+            console.info('--------CHANGE IN AUDIO STATE----------RUNNING--------------');
+            console.info('Audio State is : Running');
+            break;
+        case audio.AudioState.STATE_STOPPED:
+            console.info('--------CHANGE IN AUDIO STATE----------STOPPED--------------');
+            console.info('Audio State is : stopped');
+            break;
+        case audio.AudioState.STATE_RELEASED:
+            console.info('--------CHANGE IN AUDIO STATE----------RELEASED--------------');
+            console.info('Audio State is : released');
+            break;
+        default:
+            console.info('--------CHANGE IN AUDIO STATE----------INVALID--------------');
+            console.info('Audio State is : invalid');
+            break;
+        }
+    });
+
+   ```
+
+3. Call the **start()** function on the AudioCapturer instance to start/resume the recording task.\
+   The capturer state will be STATE_RUNNING once the start is complete. The application can then begin reading buffers.
+   ```
+    await audioCapturer.start();
+    if (audioCapturer.state == audio.AudioState.STATE_RUNNING) {
+        console.info('AudioRecLog: Capturer started');
+    } else {
+        console.info('AudioRecLog: Capturer start failed');
+    }
+
+   ```
+
+4. Obtain the minimum buffer size to read using the **getBufferSize()** API.
+   ```
+    var bufferSize = await audioCapturer.getBufferSize();
+    console.info('AudioRecLog: buffer size: ' + bufferSize);
+
+    ```
+
+5. Read the captured audio data and convert it to a byte stream. Call the **read()** API repeatedly to read the data
+   until the application wants to stop the recording. The following example shows how to write recorded data into a file.
+   ```
+    import fileio from '@ohos.fileio';
+
+    const path = '/data/data/.pulse_dir/capture_js.wav';
+    let fd = fileio.openSync(path, 0o102, 0o777);
+    if (fd !== null) {
+        console.info('AudioRecLog: file fd created');
+    }
+    else{
+        console.info('AudioRecLog: file fd create : FAILED');
+        return;
+    }
+
+    fd = fileio.openSync(path, 0o2002, 0o666);
+    if (fd !== null) {
+        console.info('AudioRecLog: file fd opened in append mode');
+    }
+
+    var numBuffersToCapture = 150;
+    while (numBuffersToCapture) {
+        var buffer = await audioCapturer.read(bufferSize, true);
+        if (typeof(buffer) == undefined) {
+            console.info('read buffer failed');
+        } else {
+            var number = fileio.writeSync(fd, buffer);
+            console.info('AudioRecLog: data written: ' + number);
+        }
+
+        numBuffersToCapture--;
+    }
+   ```
+6. Once the recording is complete, call the **stop()** API on the AudioCapturer instance to stop the recording.
+   ```
+    await audioCapturer.stop();
+    if (audioCapturer.state == audio.AudioState.STATE_STOPPED) {
+        console.info('AudioRecLog: Capturer stopped');
+    } else {
+        console.info('AudioRecLog: Capturer stop failed');
+    }
+   ```
+
+7. After the recording task is complete, call the **release()** API on the AudioCapturer instance to release the stream resources.
+   ```
+    await audioCapturer.release();
+    if (audioCapturer.state == audio.AudioState.STATE_RELEASED) {
+        console.info('AudioRecLog: Capturer released');
+    } else {
+        console.info('AudioRecLog: Capturer release failed');
+    }
+   ```
+
+## **Importance of State Check**
+Application developers should keep in mind that an AudioCapturer is state-based.
+That is, the AudioCapturer has an internal state that the application must always check when calling recorder control APIs, because some operations are only acceptable while the capturer is in a given state.\
+The system may throw an error/exception or generate other undefined behaviour if the application performs an operation while capturer is in an improper state.
+
+## **Other APIs**
+See [**js-apis-audio.md**](https://gitee.com/openharmony/docs/blob/master/en/application-dev/reference/apis/js-apis-audio.md) for more useful APIs like **getAudioTime**, **getCapturerInfo** and **getStreamInfo**.