CODEWITHSUNDEEP
androidaudiophone-call
ventres
ventres

Reputation: 291

Stream audio to a phone call Android

I am attempting to send an audio stream out over a phone call on Android.

For example, to create an app which would play some custom on-hold music, or answer a call and play a recording/audio file. I know it is possible to have an app automatically answer a call, but can it send audio to the caller?

If it is possible, please let me know what classes/functions handle this.

Upvotes: 28

Views: 29560

Answers (7)

VisualPlugin Rōblox
VisualPlugin Rōblox

Reputation: 23

Following up with a previous answer.

There was research being done in 2018 on forwarding custom audio to the Xiaomi Redmi Note 3:

https://xdaforums.com/t/direct-audio-playback-through-alsa.3806297/

More info can be found there.

First of all, you need your card name. You can get it from /proc/asound/cards. For example:

0 [msm8976tashalit]:
msm8976-tashali - msm8976-tashalite-snd-card
                  msm8976-tashalite-snd-card

card name will be "msm8976-tashalite-snd-card". Next thing is paths. You need to figure out how codec needs to be prepared. This info lies in mixer_paths.xml in /system/etc or /vendor/etc. Search for paths called deep-buffer-playback, low-latency-playback, compress-offload-playback, etc. Put values from there to "device" section. And a device number. See /proc/asound/pcm. Example:

00-09: (Compress1) :  : playback 1

Device number is 9. Volume is hard one because android changes it with software, so you can't see any difference when dumping control vars (at least in my case). Use AlsaMixer and guess... This blog post can help you: https://arunraghavan.net/2016/01/audio-devices-and-configuration/

Upvotes: 0

Saqib
Saqib

Reputation: 2283

I know the apps that are already sending all system audio to phone's earpiece even the songs you plays in your media player without root or any other special permission.

After some research I found that it can be done using Audio Manager class. For example

 AudioManager audioManager = (AudioManager) getSystemService(Context.AUDIO_SERVICE);
 audioManager.setMode(AudioManager.MODE_IN_COMMUNICATION);
 audioManager.setSpeakerphoneOn(false);

Why not to set default output speakers as device earpiece and then play audio using MediaPlayer class?

Upvotes: 1

Tim Hallman
Tim Hallman

Reputation: 894

This must be possible because phones will allow Bluetooth to send audio as a microphone.

Since I need to solve this problem one idea I have is to essentially send a bluetooth signal to myself "cloaked" as a microphone input.

Another idea (apologies if it sucks) is to reverse the speaker as a microphone. Since it seems the speaker has access to the hardware required, there may be a way to inject the audio data stream that way.

Since I'm entirely new to coding on Androids with the SDK please excuse the initial botchery of this post, I'll update as I/we figure this out.

Upvotes: 3

Lilo
Lilo

Reputation: 640

To get the audio data is very possible, but to write audio to upstreaming channel, that's not possible

Upvotes: 0

Dr. Abhishek
Dr. Abhishek

Reputation: 158

Capturing the remote submix audio requires the CAPTURE_AUDIO_OUTPUT permission. This permission is reserved for use by system components and is not available to third-party applications:(

Upvotes: 0

kieran
kieran

Reputation: 401

Writing to the phone call stream IS possible, but not from the app level on a stock (non rooted) phone.

When a phone call is initiated the mic is "typically" (really depends on the specific phone) routed directly to the baseband, ie skipping the main processor altogether.

For outgoing audio: mic->codec->baseband For incoming audio: baseband->codec->speaker

If it were always routed: mic->codec->mainprocessor->codec->baseband

Then the stream would be "presumably" available if the Android APIs (frameworks) supported accessing it.

The reason I say it is possible is because the audio (for nearly all smartphones now) is connected via SlimBus This allows dynamic changing of audio paths. It is however done in the kernel via the codec driver living in ALSA.

So.... were you so motivated, you could get the source for the Linux kernel for a phone and modify the codec/ALSA driver to allow you to change what happens when the call audio path is setup.

Of course then you would incur latency with the new path, breaking the call/latency standards AT&T setup (that Audience helped them write...) and the baseband chip might reject your audio as it's not timely.

Lastly you would need to modify the Android source (frameworks) to grow the API to support injecting audio onto that stream. (You'd need to make big mods to mediaserver, audioflinger in particular...)

It's complicated, but there is your answer. Cheers, :-)

Upvotes: 30

Konstantin Burov
Konstantin Burov

Reputation: 69238

Writing to phone call stream is not possible, sorry.

Upvotes: -5

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