Develop Reference

Android - can I direct midi output of MediaPlayer to Bluetooth

I am new to Android development, and would like to know if it is possible to send a midi file data out of Bluetooth?
I am using the following to load and start a midi file..
MediaPlayer mediaPlayer;
String music = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MUSIC).getAbsolutePath();
mediaPlayer = MediaPlayer.create(MainActivity.this, Uri.parse(music + "/test.mid"));
mediaPlayer.start();
After requesting permissions etc, this will start playing the midi file on my device.
My next step it to send this out via Bluetooth, i.e. I want just the midi going to blue tooth and NOT any other audio that may be playing on my device (in another application).
How can this be done (if it can be done)?
Edit 1
Just a bit more info that may have not been clear.
What I am after is sending midi data, NOT midi audio. Ie I want to load a midi file, and then send via Bluetooth to a Bluetooth midi cable like this, which is plugged into a keyboard, and have the midi file play the keyboard.

Android Call Recording Downlink muted

I am trying to record both Uplink and Downlink voice using Android. Regardless the law and everything, i am already aware, so please do not put comments related to the law.
The code below works fine, except when i mute the microphone, it wont record the downlink voice.
I am using Android 8.1. I've tried using a third party app called ACR on the same device, and it works fine, while i am muted, it still records the downlink voice.
val audioManager = applicationContext.getSystemService(Context.AUDIO_SERVICE) as AudioManager
val maximumVolume = audioManager.getStreamMaxVolume(AudioManager.STREAM_VOICE_CALL)
audioManager.setStreamVolume(AudioManager.STREAM_VOICE_CALL, maximumVolume, 0)
val audioSource = MediaRecorder.AudioSource.MIC
val mediaRecorder = MediaRecorder()
mediaRecorder.apply {
setAudioSource(audioSource)
setOutputFormat(MediaRecorder.OutputFormat.MPEG_4)
setAudioEncoder(MediaRecorder.AudioEncoder.AAC)
setAudioChannels(audioChannels)
setAudioSamplingRate(audioSamplingRate)
setAudioEncodingBitRate(audioEncodingBitRate)
setOutputFile(path)
prepare()
start()

This is not an issue. You set the MediaRecorder to use MIC as input, so if you MUTE the microphone it's obliviously that the input signat is lost/muted. When you use "downlink" word I expected to see a different input source as VOICECALL or DOWNLINK instead of MIC. Trying to record a voicecall using the MIC it's wrong in my opinion because: (1) you have to set max volume to speaker and redirect the voicecall through it (2) while recording a voicecall from the MIC the caller hears ALL what it happens around your device and all what you're saying to other people (3) this method records much noise and echoes. The right way is to record from VOICECALL but most of new devices (using newer Android version) prevents to record from this source and allows it only at System Apps. ACR uses a workaround by calling hidden API methods, but this method could stop stop work at any time due to Android updates.

Distinguish source when capturing audio with AudioRecord

The AudioRecord class allows recording of phone calls with one of the following options as the recording source:
VOICE_UPLINK: The audio transmitted from your end to the other party. IOW, what you speak into the microphone.
VOICE_DOWNLINK: The audio transmitted from the other party to your end.
VOICE_CALL: VOICE_UPLINK + VOICE_DOWNLINK.
I'd like to build an App that records both VOICE_UPLINK & VOICE_DOWNLINK and identify the source of the voice.
When using VOICE_CALL as the AudioSource option, the UP/DOWN-LINK streams are bundled together in to the received data buffer which makes it hard to identify the source of the voice.
Using two AudioRecords with VOICE_UPLINK & VOICE_DOWNLINK does not work - the second AudioRecord fails to start because the first AudioRecord locks the recording stream.
Is there any creative way to bypass the locking problem presented at case (2), thus enable recording of the VOICE_UPLINK & VOICE_DOWNLINK streams simultaneously and easily identifying the source?

Recording voice calls in android

I want to make an app that records incoming and outgoing calls. I am using the media recorder to do so and also I am using service/broadcastreceiver to detect phone state change. I have set the audio source as Audiosource.VOICE_CALLS.I am able to record voices at my end but not from the other end. The same happens when the audio source is set as Audiosource.MIC.
Please suggest a solution.

You cannot access the incall audio stream in Android using the public SDK. Call audio is not exposed to apps, and you can only do this if you modify Android at a source level, and then build and install a new image from the customized source to your device.

Sounds doesn't come out from the phone when I play them during the call through the coding?

I have tested my app: it starts playing a song by getting incoming call on external speaker with enough volume to make person on another side to listen what we play on our side.
But when I answer a call, the playing song stops. I want the song to be playing during call so the person on the other side can hear it.
I would appreciate any suggestion from anyone if they has also faced this problem or know a solution.

That's because while you're in a call, media playback routing will follow the voice call routing. And the default output routing for voice calls if you don't have any accessories attached is to use the earpiece.
You could try waiting for the phone state to switch to MODE_IN_CALL, and then use setSpeakerPhoneOn to change the output routing to use the loudspeaker. Note that this will also route the voice call audio to the loudspeaker, not just the media audio.
EDIT: You could try using the stream type ENFORCED_AUDIBLE (integer value 7) for your media playback. However, it might not work across all devices / all Android versions.