It is necessary to get sound level value to test microphone before streaming. The standard class android.media.MediaRecorder can be used to do that. In this case, audio data should be recorded to a file. Android 10 and lower allows recording to the pseudodevice /dev/null. but in Android 11 and newer this is impossible, and a real file stored in application data must be used:

code

            mRecorder = new MediaRecorder();
            mRecorder.setAudioSource(MediaRecorder.AudioSource.MIC);
            mRecorder.setOutputFormat(MediaRecorder.OutputFormat.THREE_GPP);
            mRecorder.setAudioEncoder(MediaRecorder.AudioEncoder.AMR_NB);
            String fileName = context.getFilesDir().getAbsolutePath() + "/test.3gp";
            //Path /dev/null throw exception on Android 11
            mRecorder.setOutputFile(fileName);

            try {
                mRecorder.prepare();
            } catch (IllegalStateException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

            mRecorder.start();

An instantaneous value of sound amplitude may be received from MediaRecorder object

code

    public double getAmplitude() {
        if (mRecorder != null)
            return (mRecorder.getMaxAmplitude() / 2700.0);
        else
            return 0;

    }

and then average this value to display it

code

    static final private double EMA_FILTER = 0.6;
    private double mEMA = 0.0;
    ...
    public double getAmplitudeEMA() {
        double amp = getAmplitude();
        mEMA = EMA_FILTER * amp + (1.0 - EMA_FILTER) * mEMA;
        return mEMA;
    }