Android Open Source - gdk-waveform-sample Waveform Activity

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License

The source code is released under:

Apache License

Java Source Code

/*
 * Copyright (C) 2013 Google Inc./*  w  ww .j  a va  2 s .  co m*/
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.android.glass.sample.waveform;

import android.app.Activity;
import android.media.AudioFormat;
import android.media.AudioRecord;
import android.media.MediaRecorder.AudioSource;
import android.os.Bundle;
import android.widget.TextView;

/**
 * Receives audio input from the microphone and displays a visualization of that data as a waveform
 * on the screen.
 */
public class WaveformActivity extends Activity {

    // The sampling rate for the audio recorder.
    private static final int SAMPLING_RATE = 44100;

    private WaveformView mWaveformView;
    private TextView mDecibelView;

    private RecordingThread mRecordingThread;
    private int mBufferSize;
    private short[] mAudioBuffer;
    private String mDecibelFormat;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.layout_waveform);

        mWaveformView = (WaveformView) findViewById(R.id.waveform_view);
        mDecibelView = (TextView) findViewById(R.id.decibel_view);

        // Compute the minimum required audio buffer size and allocate the buffer.
        mBufferSize = AudioRecord.getMinBufferSize(SAMPLING_RATE, AudioFormat.CHANNEL_IN_MONO,
                AudioFormat.ENCODING_PCM_16BIT);
        mAudioBuffer = new short[mBufferSize / 2];

        mDecibelFormat = getResources().getString(R.string.decibel_format);
    }

    @Override
    protected void onResume() {
        super.onResume();

        mRecordingThread = new RecordingThread();
        mRecordingThread.start();
    }

    @Override
    protected void onPause() {
        super.onPause();

        if (mRecordingThread != null) {
            mRecordingThread.stopRunning();
            mRecordingThread = null;
        }
    }

    /**
     * A background thread that receives audio from the microphone and sends it to the waveform
     * visualizing view.
     */
    private class RecordingThread extends Thread {

        private boolean mShouldContinue = true;

        @Override
        public void run() {
            android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_AUDIO);

            AudioRecord record = new AudioRecord(AudioSource.MIC, SAMPLING_RATE,
                    AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_16BIT, mBufferSize);
            record.startRecording();

            while (shouldContinue()) {
                record.read(mAudioBuffer, 0, mBufferSize / 2);
                mWaveformView.updateAudioData(mAudioBuffer);
                updateDecibelLevel();
            }

            record.stop();
            record.release();
        }

        /**
         * Gets a value indicating whether the thread should continue running.
         *
         * @return true if the thread should continue running or false if it should stop
         */
        private synchronized boolean shouldContinue() {
            return mShouldContinue;
        }

        /** Notifies the thread that it should stop running at the next opportunity. */
        public synchronized void stopRunning() {
            mShouldContinue = false;
        }

        /**
         * Computes the decibel level of the current sound buffer and updates the appropriate text
         * view.
         */
        private void updateDecibelLevel() {
            // Compute the root-mean-squared of the sound buffer and then apply the formula for
            // computing the decibel level, 20 * log_10(rms). This is an uncalibrated calculation
            // that assumes no noise in the samples; with 16-bit recording, it can range from
            // -90 dB to 0 dB.
            double sum = 0;

            for (short rawSample : mAudioBuffer) {
                double sample = rawSample / 32768.0;
                sum += sample * sample;
            }

            double rms = Math.sqrt(sum / mAudioBuffer.length);
            final double db = 20 * Math.log10(rms);

            // Update the text view on the main thread.
            mDecibelView.post(new Runnable() {
                @Override
                public void run() {
                    mDecibelView.setText(String.format(mDecibelFormat, db));
                }
            });
        }
    }
}

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