I am writing a new Android Audio HAL, to let my App to feed audio to other apps, to allow my handheld remote microphone input to reach Google app. Essentially, a Virtual Audio Cable.
Its a work in progress. I'll probably be overriding AUDIO_DEVICE_IN_BACK_MIC, but this is open for suggestions.
I have doubts on how to make sure Android uses this HAL for input.
Do I need to replace audio.primary.default.so or should I leave it as audio.vcable.default.so?
More specifically: If I am not replacing primary, how will Android know to use my HAL instead of primary?
Update:
I could really use any help in this work. Any pointers are helpful.
I have written an Audio HAL module. I have added following (bold items) to audio_policy.conf:
global:
global_configuration {
attached_output_devices AUDIO_DEVICE_OUT_SPEAKER|**AUDIO_DEVICE_OUT_LINE**
default_output_device AUDIO_DEVICE_OUT_SPEAKER
attached_input_devices AUDIO_DEVICE_IN_BUILTIN_MIC|AUDIO_DEVICE_IN_BACK_MIC|AUDIO_DEVICE_IN_REMOTE_SUBMIX|**AUDIO_DEVICE_IN_LINE**
}
and under audio_hw_modules
vloop {
inputs {
vloop {
sampling_rates 16000
channel_masks AUDIO_CHANNEL_IN_MONO
formats AUDIO_FORMAT_PCM_16_BIT
devices AUDIO_DEVICE_IN_LINE
}
}
outputs {
vloop {
sampling_rates 16000
channel_masks AUDIO_CHANNEL_OUT_STEREO
formats AUDIO_FORMAT_PCM_16_BIT
devices AUDIO_DEVICE_OUT_LINE
flags AUDIO_OUTPUT_FLAG_DIRECT
}
}
}
I also added following (bold) to AudioFlinger.cpp
static const char * const audio_interfaces[] = {
AUDIO_HARDWARE_MODULE_ID_PRIMARY,
AUDIO_HARDWARE_MODULE_ID_A2DP,
AUDIO_HARDWARE_MODULE_ID_USB,
**AUDIO_HARDWARE_MODULE_ID_VLOOP**
};
I can see that during boot, my HAL gets loaded, and I get these logs:
10-06 06:14:40.365 194-194/? I/AudioFlinger: Using default 3000 mSec as standby time.
10-06 06:14:46.664 194-194/? I/AudioPolicyService: AudioPolicyService CSTOR in new mode
10-06 06:14:46.673 194-194/? I/APM::ConfigParsingUtils: loadAudioPolicyConfig() loaded /system/etc/audio_policy.conf
10-06 06:14:46.681 194-194/? D/audio_hw_primary: adev_open: enter
10-06 06:14:46.797 194-194/? I/AudioFlinger: loadHwModule() Loaded primary audio interface from QCOM Audio HAL (audio) handle 1
10-06 06:14:46.797 194-194/? I/AudioFlinger: openOutput(), module 1 Device 2, SamplingRate 48000, Format 0x000001, Channels 3, flags 2
10-06 06:14:46.797 194-194/? I/AudioFlinger: AudioStreamOut::open(), mHalFormatIsLinearPcm = 1
10-06 06:14:46.798 194-194/? I/AudioFlinger: HAL output buffer size 240 frames, normal sink buffer size 960 frames
10-06 06:14:46.813 194-194/? I/AudioFlinger: Using module 1 has the primary audio interface
10-06 06:14:46.816 194-607/? I/AudioFlinger: AudioFlinger's thread 0xb4140000 ready to run
10-06 06:14:46.816 194-607/? D/audio_hw_primary: out_set_parameters: enter: usecase(1: low-latency-playback) kvpairs: routing=2
10-06 06:14:46.818 194-194/? I/AudioFlinger: openOutput(), module 1 Device 2, SamplingRate 48000, Format 0x000001, Channels 3, flags 8
10-06 06:14:46.818 194-194/? I/AudioFlinger: AudioStreamOut::open(), mHalFormatIsLinearPcm = 1
10-06 06:14:46.818 194-194/? I/AudioFlinger: HAL output buffer size 960 frames, normal sink buffer size 960 frames
10-06 06:14:46.818 194-608/? I/AudioFlinger: AudioFlinger's thread 0xb3dc0000 ready to run
10-06 06:14:46.818 194-607/? E/AudioFlinger: no wake lock to update!
10-06 06:14:46.818 194-608/? D/audio_hw_primary: out_set_parameters: enter: usecase(0: deep-buffer-playback) kvpairs: routing=2
10-06 06:14:46.818 194-608/? E/AudioFlinger: no wake lock to update!
10-06 06:14:46.820 194-609/? I/AudioFlinger: AudioFlinger's thread 0xb3c40000 ready to run
10-06 06:14:46.823 194-194/? I/AudioFlinger: loadHwModule() Loaded a2dp audio interface from A2DP Audio HW HAL (audio) handle 7
10-06 06:14:46.828 194-194/? I/AudioFlinger: loadHwModule() Loaded usb audio interface from USB audio HW HAL (audio) handle 8
10-06 06:14:46.832 194-194/? I/r_submix: adev_open(name=audio_hw_if)
10-06 06:14:46.832 194-194/? I/AudioFlinger: loadHwModule() Loaded r_submix audio interface from Wifi Display audio HAL (audio) handle 9
10-06 06:14:46.832 194-194/? D/r_submix: submix_audio_device_create_pipe_l(addr=0, idx=9)
10-06 06:14:46.833 194-610/? I/AudioFlinger: AudioFlinger's thread 0xb3bc0000 ready to run
10-06 06:14:46.833 194-194/? D/r_submix: submix_audio_device_release_pipe_l(idx=9) addr=0
10-06 06:14:46.833 194-194/? D/r_submix: submix_audio_device_destroy_pipe_l(): pipe destroyed
10-06 06:14:46.835 194-194/? D/audio_vloop: adev_open: audio_hw_if
10-06 06:14:46.835 194-194/? D/audio_vloop: adev_open(): 1678
10-06 06:14:46.835 194-194/? D/audio_vloop: adev_open(): 1685
10-06 06:14:46.835 194-194/? D/audio_vloop: adev_open(): 1688
10-06 06:14:46.835 194-194/? D/audio_vloop: adev_open(): 1722
10-06 06:14:46.835 194-194/? D/audio_vloop: adev_init_check(): 1252
10-06 06:14:46.835 194-194/? D/audio_vloop: adev_set_master_volume: 1.000000
10-06 06:14:46.835 194-194/? D/audio_vloop: adev_set_master_mute: 0
10-06 06:14:46.835 194-194/? I/AudioFlinger: loadHwModule() Loaded vloop audio interface from UI_audio_HW_HAL (audio) handle 11
10-06 06:14:46.835 194-194/? D/audio_vloop: adev_open_input_stream(): 1490
10-06 06:14:46.835 194-194/? D/audio_vloop: in_get_sample_rate(): 979
10-06 06:14:46.835 194-194/? D/audio_vloop: in_get_channels(): 1017
10-06 06:14:46.835 194-194/? D/audio_vloop: in_get_channels: 0x00000001
10-06 06:14:46.835 194-194/? D/audio_vloop: in_get_format(): 1029
10-06 06:14:46.836 194-194/? D/audio_vloop: in_get_format: 0x00000001
10-06 06:14:46.836 194-194/? D/audio_vloop: in_get_format(): 1029
10-06 06:14:46.836 194-194/? D/audio_vloop: in_get_format: 0x00000001
10-06 06:14:46.836 194-194/? D/audio_vloop: in_get_channels(): 1017
10-06 06:14:46.836 194-194/? D/audio_vloop: in_get_channels: 0x00000001
10-06 06:14:46.836 194-194/? D/audio_vloop: in_get_buffer_size(): 1005
10-06 06:14:46.836 194-194/? D/audio_vloop: in_get_buffer_size: 1600
10-06 06:14:46.836 194-194/? D/audio_vloop: in_get_buffer_size(): 1005
10-06 06:14:46.836 194-194/? D/audio_vloop: in_get_buffer_size: 1600
10-06 06:14:46.836 194-194/? D/audio_vloop: in_get_format(): 1029
10-06 06:14:46.836 194-194/? D/audio_vloop: in_get_format: 0x00000001
10-06 06:14:46.836 194-194/? D/audio_vloop: in_get_sample_rate(): 979
10-06 06:14:46.836 194-194/? D/audio_vloop: in_get_channels(): 1017
10-06 06:14:46.836 194-194/? D/audio_vloop: in_get_channels: 0x00000001
10-06 06:14:46.838 194-613/? I/AudioFlinger: AudioFlinger's thread 0xb3bc0000 ready to run
10-06 06:14:46.838 194-194/? D/audio_vloop: adev_close_input_stream(): 1570
10-06 06:14:46.839 194-194/? W/APM::AudioPolicyManager: Input device 00020000 unreachable
10-06 06:14:46.839 194-611/? D/audio_vloop: looper_thread(): 216: Entered
10-06 06:14:46.839 194-611/? D/audio_vloop: looper_thread(): 366: Exiting
10-06 06:15:07.137 616-616/? I/InputManager: Initializing input manager, mUseDevInputEventForAudioJack=false
10-06 06:15:10.155 616-616/? I/SystemServer: Audio Service
10-06 06:15:10.222 194-607/? E/AudioFlinger: no wake lock to update!
10-06 06:15:10.222 194-608/? E/AudioFlinger: no wake lock to update!
10-06 06:15:10.224 194-614/? D/audio_hw_primary: adev_set_mic_mute: state 0
10-06 06:15:10.224 194-614/? D/audio_vloop: adev_set_mic_mute: 0
10-06 06:15:14.061 194-614/? D/audio_hw_primary: adev_set_parameters: enter: A2dpSuspended=false
10-06 06:15:14.061 194-614/? D/audio_vloop: adev_set_parameters(): [A2dpSuspended=false]
10-06 06:15:14.084 194-194/? I/AudioFlinger: systemReady
10-06 06:15:16.308 194-194/? D/audio_hw_primary: adev_set_mic_mute: state 0
10-06 06:15:16.308 194-194/? D/audio_vloop: adev_set_mic_mute: 0
10-06 06:15:17.072 194-194/? D/audio_hw_primary: adev_set_parameters: enter: A2dpSuspended=false
10-06 06:15:17.072 194-194/? D/audio_vloop: adev_set_parameters(): [A2dpSuspended=false]
10-06 06:15:25.023 733-733/? W/AudioTrack: AUDIO_OUTPUT_FLAG_FAST denied by client; transfer 4, track 44100 Hz, output 48000 Hz
10-06 06:15:25.032 194-607/? D/audio_hw_primary: out_set_parameters: enter: usecase(1: low-latency-playback) kvpairs: routing=2
10-06 06:15:25.043 194-607/? D/audio_hw_primary: select_devices: out_snd_device(2: speaker) in_snd_device(0: none)
10-06 06:15:25.043 194-607/? D/audio_hw_primary: enable_snd_device: snd_device(2: speaker)
10-06 06:15:25.050 194-607/? D/audio_hw_primary: enable_audio_route: apply and update mixer path: low-latency-playback
10-06 06:15:26.431 1150-1298/? I/MicrophoneInputStream: mic_starting com.google.android.apps.gsa.speech.audio.ag@c6eb0e1
10-06 06:15:26.443 194-1585/? I/AudioFlinger: AudioFlinger's thread 0xb3bc0000 ready to run
10-06 06:15:26.447 1150-1298/? I/MicrophoneInputStream: mic_started com.google.android.apps.gsa.speech.audio.ag@c6eb0e1
10-06 06:15:26.457 194-1585/? D/audio_hw_primary: select_devices: out_snd_device(0: none) in_snd_device(38: voice-rec-mic)
10-06 06:15:26.457 194-1585/? D/audio_hw_primary: enable_snd_device: snd_device(38: voice-rec-mic)
10-06 06:15:26.460 194-1585/? D/audio_hw_primary: enable_audio_route: apply and update mixer path: audio-record
10-06 06:15:26.942 1150-1271/? I/AudioController: internalShutdown
10-06 06:15:26.943 1150-1271/? I/MicrophoneInputStream: mic_close com.google.android.apps.gsa.speech.audio.ag@c6eb0e1
10-06 06:15:26.943 1150-1298/? E/AudioRecord-JNI: Error -4 during AudioRecord native read
10-06 06:15:26.986 194-1585/? D/audio_hw_primary: disable_audio_route: reset and update mixer path: audio-record
10-06 06:15:26.987 194-1585/? D/audio_hw_primary: disable_snd_device: snd_device(38: voice-rec-mic)
10-06 06:15:27.066 194-607/? D/audio_hw_primary: out_set_parameters: enter: usecase(1: low-latency-playback) kvpairs: routing=2
10-06 06:15:27.100 194-607/? D/AudioFlinger: mixer(0xb4140000) throttle end: throttle time(7)
10-06 06:15:30.257 194-607/? D/audio_hw_primary: disable_audio_route: reset and update mixer path: low-latency-playback
10-06 06:15:30.257 194-607/? D/audio_hw_primary: disable_snd_device: snd_device(2: speaker)
10-06 06:15:30.262 194-607/? D/audio_hw_primary: out_set_parameters: enter: usecase(1: low-latency-playback) kvpairs: routing=2
10-06 06:15:30.272 194-607/? D/audio_hw_primary: select_devices: out_snd_device(2: speaker) in_snd_device(0: none)
10-06 06:15:30.273 194-607/? D/audio_hw_primary: enable_snd_device: snd_device(2: speaker)
10-06 06:15:30.280 194-607/? D/audio_hw_primary: enable_audio_route: apply and update mixer path: low-latency-playback
10-06 06:15:30.347 194-607/? D/AudioFlinger: mixer(0xb4140000) throttle end: throttle time(10)
10-06 06:15:31.517 194-607/? D/audio_hw_primary: out_set_parameters: enter: usecase(1: low-latency-playback) kvpairs: routing=2
10-06 06:15:31.751 1150-1298/? I/MicrophoneInputStream: mic_starting com.google.android.apps.gsa.speech.audio.ag@dd13203
10-06 06:15:31.762 194-1826/? I/AudioFlinger: AudioFlinger's thread 0xb3bc0000 ready to run
10-06 06:15:31.771 1150-1298/? I/MicrophoneInputStream: mic_started com.google.android.apps.gsa.speech.audio.ag@dd13203
10-06 06:15:31.780 194-1826/? D/audio_hw_primary: select_devices: out_snd_device(0: none) in_snd_device(38: voice-rec-mic)
10-06 06:15:31.780 194-1826/? D/audio_hw_primary: enable_snd_device: snd_device(38: voice-rec-mic)
10-06 06:15:31.783 194-1826/? D/audio_hw_primary: enable_audio_route: apply and update mixer path: audio-record
10-06 06:15:34.695 194-607/? D/audio_hw_primary: disable_audio_route: reset and update mixer path: low-latency-playback
10-06 06:15:34.695 194-607/? D/audio_hw_primary: disable_snd_device: snd_device(2: speaker)
10-06 06:15:34.850 1150-1271/? I/AudioController: internalShutdown
10-06 06:15:34.851 1150-1271/? I/MicrophoneInputStream: mic_close com.google.android.apps.gsa.speech.audio.ag@dd13203
10-06 06:15:34.851 1150-1298/? E/AudioRecord-JNI: Error -4 during AudioRecord native read
10-06 06:15:34.885 194-1826/? D/audio_hw_primary: disable_audio_route: reset and update mixer path: audio-record
10-06 06:15:34.885 194-1826/? D/audio_hw_primary: disable_snd_device: snd_device(38: voice-rec-mic)
Mine is audio_vloop. I can see that Android opens my device, then opens input stream, and then closes the input stream. It never attempts to open output stream. audio_vloop implements both input and output streams. After this, nothing in audio_vloop is ever invoked by Android.
I made a small app that plays audio (from a pcm file for now). I want to redirect this output to my HAL. To achieve this, I believe I need to do a AudioTrack.setPreferredDevice() on my audio track. I found that Audio Manager should have a list of all audio devices.
so I call :
AudioDeviceInfo aDevInfo[] = am.getDevices(AudioManager.GET_DEVICES_OUTPUTS);
It only finds 1 device, more info on this device:
10-06 06:37:01.962 3295-3663/? D/AudioPlayer: Have [1] devices
10-06 06:37:01.964 3295-3663/? D/AudioPlayer: devInfo[0]: [Landroid.media.AudioDeviceInfo;@90bd9da
10-06 06:37:01.965 3295-3663/? D/AudioPlayer: getProductName()AOSP on Flo
10-06 06:37:01.965 3295-3663/? D/AudioPlayer: getType()2
10-06 06:37:01.966 3295-3663/? D/AudioPlayer: isSink()true
10-06 06:37:01.966 3295-3663/? D/AudioPlayer: isSource()false
This seemingly is from audioPort which I have not implemented. So its not from my HAL.
I've obviously missed one or more steps before Android will allow my app to talk to my device.
I need to be able to send audio from my app into my HAL. Later, I also need to be able to receive audio from my HAL (through AudioRecord etc).
What did I missed in integrating my HAL into Android? Do I need to implement Audio Ports? Is something else required?
Update 2
I found there is a typo in AOSP, in AudioPolicyManager.cpp@2922
Instead of Output, it prints Input
I had this log AudioPolicyManager: Input device 00020000 unreachable which I disregarded assuming it is talking about BT/A2DP input device.
I fixed the log for my device, and it turns out to be Line out device which we want to use. I am debugging this direction now.
Found answers.
For out stream:
- Outputs that don't support
AUDIO_CHANNEL_OUT_STEREOare not being opened by Android Outputs that mention flag
AUDIO_OUTPUT_FLAG_DIRECTare not opened by Android automatically. This is evident in following code inAudioPolicyManager.cppif ((outProfile->mFlags & AUDIO_OUTPUT_FLAG_DIRECT) != 0) { continue; }from here
There may be a way to open them in programatically, but I have not found answer to that.
These two, once fixed were sufficient for Android to start using my out stream.
For in stream:
In stream was already a part of results of AudioManager.getDevices()
So it was possible to read from vloop in stream after AudioTrack.setPreferredDevice().
To ensure that other apps will read mic input from vloop, I had to declare it to implement AUDIO_DEVICE_IN_BUILTIN_MIC. For this to work, I also removed AUDIO_DEVICE_IN_BUILTIN_MIC from primary HAL in audio_policy.conf.
Additionally, I made in stream stereo only to maintain compatibility with out stream buffer format.
After these changes, I see that there are continuous read and write calls coming to vloop.
UPDATE:
I later found that above mentioned behavior is dependent on Audio Policy Manager implementation. Most of them behave same way, (e.g. most open INBUILT_MIC for VOICE_RECOGNITION input) but some may not (Nexus Player) For these outliers, either implemnent what their APMs open, or modify APMs to open what your HAL implements.
来源：https://stackoverflow.com/questions/39746221/what-is-required-to-make-android-use-a-new-audio-hal