(Android/Kotlin) Record Audio from MIC to .3GP file (that can be read with VLC).

MainActivity.kt

// https://ntic974.blogspot.com

package com.reuniware.poneyvid

import android.Manifest
import android.content.Context
import android.content.Intent
import android.content.pm.PackageManager
import android.media.MediaRecorder
import android.media.projection.MediaProjection
import android.media.projection.MediaProjectionManager
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.os.Environment
import androidx.core.app.ActivityCompat
import kotlinx.android.synthetic.main.activity_main.*

class MainActivity : AppCompatActivity() {

    val REQUEST_MEDIA_PROJECTION = 5555
    val REQUEST_AUDIO = 7777
    val REQUEST_STORAGE = 9999
    lateinit var manager : MediaProjectionManager
    lateinit var projection : MediaProjection
    lateinit var recorder : MediaRecorder

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.RECORD_AUDIO) != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(
                this,
                arrayOf(Manifest.permission.RECORD_AUDIO),
                REQUEST_AUDIO
            )
        }

        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(
                this,
                arrayOf(Manifest.permission.WRITE_EXTERNAL_STORAGE),
                REQUEST_STORAGE
            )
        }

        if (!::manager.isInitialized) {
            manager = getSystemService(Context.MEDIA_PROJECTION_SERVICE) as MediaProjectionManager
            startActivityForResult(manager.createScreenCaptureIntent(), REQUEST_MEDIA_PROJECTION)
        }
        buttonStart.setOnClickListener {
            val PATH_NAME = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DCIM).absolutePath + "/recorded.3gp" //+ "/mavid.mp4"
            recorder = MediaRecorder()
            recorder.setAudioSource(MediaRecorder.AudioSource.MIC)
            recorder.setOutputFormat(MediaRecorder.OutputFormat.THREE_GPP)
            recorder.setAudioEncoder(MediaRecorder.AudioEncoder.AMR_NB)
            recorder.setOutputFile(PATH_NAME)
            recorder.prepare()
            recorder.start()   // Recording is now started

        }
        buttonStop.setOnClickListener {
            recorder.stop()
            recorder.reset()
            recorder.release()
        }
    }

    var resultCode_ = -1
    var data_ = Intent()

    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        super.onActivityResult(requestCode, resultCode, data)
        if (!::projection.isInitialized) {
            resultCode_ = resultCode
            data_ = data!!
            projection = manager.getMediaProjection(resultCode, data) as MediaProjection
        }
    }
}