Call recording - make it work on Nexus 5X (rooting

Question

I'm attempting to use AudioRecord with AudioSource.VOICE_DOWNLINK on Nexus 5X, Android 7.1 (my own build from AOSP).

I'm already past the permissions stage - moved my APK to privileged apps, made an adjustment to AudioRecord in Android source to stop throwing an exception about this source.

Now I'm getting empty recording buffers during a phone call.

I know that there are a lot of call recording apps, and they work on other devices. I've also seen certain apps that can perform some hack on a rooted N5 and make it work.

I wish to achieve the same on Nexus 5X - ANY adjustment is OK for me, including changing Android version, modifying Qualcomm drivers, device configuration files, etc. - basically anything that can be achieved in a custom ROM.

I've tried messing around with platform code - hardware/qcom/audio/hal/voice.c, especially the function voice_check_and_set_incall_rec_usecase, but could not make sense out of it so far.

Also checked device/lge/bullhead/mixer_paths.xml, found there's a section related to call recording:

<!-- Incall Recording -->
<ctl name="MultiMedia1 Mixer VOC_REC_UL" value="0" />
<ctl name="MultiMedia1 Mixer VOC_REC_DL" value="0" />
<ctl name="MultiMedia8 Mixer VOC_REC_UL" value="0" />
<ctl name="MultiMedia8 Mixer VOC_REC_DL" value="0" />
<!-- Incall Recording End -->

But I also couldn't make sense out of it or how it can be helped.

Answer 1

Not sure if it is a Nexus 5 specific issue but usually the class used to record calls is MediaRecorder. Have you tried to replace AudioRecorder by a MediaRecorder?

Based on this stack-overflow question, I think you could try the following code based on Ben blog post:

import android.media.MediaRecorder;
import android.os.Environment;

import java.io.File;

import java.io.IOException;


public class CallRecorder {

    final MediaRecorder recorder = new MediaRecorder();
    final String path;

    /**
     * Creates a new audio recording at the given path (relative to root of SD card).
     */
    public CallRecorder(String path) {
        this.path = sanitizePath(path);
    }

    private String sanitizePath(String path) {
        if (!path.startsWith("/")) {
            path = "/" + path;
        }
        if (!path.contains(".")) {
            path += ".3gp";
        }
        return Environment.getExternalStorageDirectory().getAbsolutePath() + path;
    }

    /**
     * Starts a new recording.
     */
    public void start() throws IOException {
        String state = android.os.Environment.getExternalStorageState();
        if(!state.equals(android.os.Environment.MEDIA_MOUNTED))  {
            throw new IOException("SD Card is not mounted.  It is " + state + ".");
        }

        // make sure the directory we plan to store the recording in exists
        File directory = new File(path).getParentFile();
        if (!directory.exists() && !directory.mkdirs()) {
            throw new IOException("Path to file could not be created.");
        }

        recorder.setAudioSource(MediaRecorder.AudioSource.VOICE_CALL);
        recorder.setOutputFormat(MediaRecorder.OutputFormat.THREE_GPP);
        recorder.setAudioEncoder(MediaRecorder.AudioEncoder.AMR_NB);
        recorder.setOutputFile(path);
        recorder.prepare();
        recorder.start();
    }

    /**
     * Stops a recording that has been previously started.
     */
    public void stop() throws IOException {
        recorder.stop();
        recorder.release();
    }

}

In this sample, I've used MediaRecorder.AudioSource.VOICE_CALL but you can test other options like MediaRecorder.AudioSource.VOICE_COMMUNICATION and also the microphone just to see if there are any hardware issues on your phone.