Why does the AudioRecord output only zeros?

I am using Java Android AudioRecorder (Code as below). When I start recording, rms is normal value larger than 0. Several seconds after recording, rms only gets 0.0 value, which means audioBuffer is a zero buffer. How can I fix it? Thanks.

        recorder = new AudioRecord(MediaRecorder.AudioSource.MIC, sampleRate, channelConfig, audioFormat, bufferSize);
        while (isRecording) {
            int read = recorder.read(audioBuffer, 0, bufferSize);
            if (read > 0) {
                long currentTime = System.currentTimeMillis();

                // Calculate the RMS (root mean square) value of the audio buffer
                double sum = 0;
                for (int i = 0; i < read; i += 2) {
                    short sample = (short) ((audioBuffer[i + 1] << 8) | (audioBuffer[i] & 0xFF));
                    sum += sample * sample;
                }
                double rms = Math.sqrt(sum / (read / 2));

And here is a more detailed version of my code:

    private void writeAudioDataToFile(String filePath, int bufferSize) {
        byte[] audioBuffer = new byte[bufferSize];
        FileOutputStream os = null;

        while (isRecording) {
            int read = recorder.read(audioBuffer, 0, bufferSize);
            if (read > 0) {
                long currentTime = System.currentTimeMillis();

                // Calculate the RMS (root mean square) value of the audio buffer
                double sum = 0;
                for (int i = 0; i < read; i += 2) {
                    short sample = (short) ((audioBuffer[i + 1] << 8) | (audioBuffer[i] & 0xFF));
                    sum += sample * sample;
                }
                double rms = Math.sqrt(sum / (read / 2));

                // Check if the audio level is above the silence threshold
                if (rms > SILENCE_THRESHOLD) {
                    lastVoiceTimestamp = currentTime;
                    Log.i(Config.TAG, "Loud.");
                    // If the output stream is null, create a new file
                    if (os == null) {
                        try {
                            os = new FileOutputStream(filePath);
                        } catch (FileNotFoundException e) {
                            e.printStackTrace();
                        }
                    }

                    // Write audio data to file
                    try {
                        os.write(audioBuffer, 0, read);
                    } catch (IOException e) {
                        e.printStackTrace();
                    }

                } else {
                    Log.i(Config.TAG, "Silent "+ String.valueOf(rms)+" "+String.valueOf(recorder.getState()));
                    // Check if silence duration has exceeded the threshold
                    if (currentTime - lastVoiceTimestamp > SILENCE_DURATION) {
                        Log.i(Config.TAG, "Silent Time Out "+ String.valueOf(rms)+" "+ String.valueOf(lastVoiceTimestamp));
                        // Close the current file and prepare for a new one
                        if (os != null) {
                            try {
                                os.close();
                            } catch (IOException e) {
                                e.printStackTrace();
                            }
                            os = null;

                            // Encode the recorded PCM data to M4A
                            String m4aFilePath = filePath.replace(".pcm", ".m4a");
                            convertPcmToM4a(filePath, m4aFilePath);
                            filePath = audioDir + "/" + "record_" + System.currentTimeMillis() + ".pcm";
                            // Trigger transcription and translation
                            new Thread(() -> {
                                triggerTranscriptionAndTranslation(m4aFilePath);
                            }).start();
                            Log.i(Config.TAG, "New audio "+ filePath);
                        }
                    } else {
                        // If within silence duration, continue writing silence (optional)
                        if (os != null) {
                            try {
                                os.write(audioBuffer, 0, read);
                            } catch (IOException e) {
                                e.printStackTrace();
                            }
                        }
                    }
                }
            }
        }

        // Clean up when recording stops
        if (os != null) {
            try {
                os.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            os = null;

            // Encode the last recorded PCM data to M4A
            String m4aFilePath = filePath.replace(".pcm", ".m4a");
            convertPcmToM4a(filePath, m4aFilePath);

            // Trigger transcription and translation
            new Thread(() -> {
                triggerTranscriptionAndTranslation(m4aFilePath);
            }).start();
        }
    }

I have logged the rms. At the beginning it is normal value larger than 0. Then suddenly it becomes 0.

It's hard to tell what exactly is wrong based on the information given. But here are a few tips:

1. Make sure that writeAudioDataToFile doesn't run on the main (UI) thread.
2. Make sure the recording happens in the foreground (in Activity or a foreground service).
3. Increase the buffer size (e.g. 2 times the minimum size).
4. You should check the result of recorder.read() and handle possible errors (e.g. AudioRecord.ERROR_BAD_VALUE, AudioRecord.ERROR_INVALID_OPERATION, etc.)
5. You might want to acquire a Wake Lock while recording.