Audio Injection on Real Devices
Test audio-driven and microphone-dependent features on real Android and iOS devices through Appium / Selenium automation. Inject pre-recorded audio files directly into the device microphone — no physical mic input required.
To enable it for your organization, please contact us via 24×7 chat support or you can also drop a mail to support@testmuai.com.
Overview
Audio Injection enables you to simulate microphone input on real devices by injecting pre-recorded audio files (MP3, WAV) into the device's mic pipeline during automated tests.
Use it to test speech-to-text, voice commands, voice assistants, in-app recording, KYC voice verification, and any other microphone-dependent feature.
Supported Platforms
| Platform | Minimum OS Version |
|---|---|
| Android | Android 13 (SDK 33) and above |
| iOS | iOS 16 and above |
Audio Injection is supported on real devices only. It is not available on emulators or simulators.
Supported File Formats
| Format | Max Size |
|---|---|
| MP3 | 200 MB |
| WAV | 200 MB |
The audio file must be uploaded to TestMu AI before it can be injected.
Step 1 - Upload Audio File
Use the Upload Media API to upload an audio file to your TestMu AI account.
curl -u "LT_USERNAME:LT_ACCESS_KEY" -X POST "https://api.lambdatest.com/mfs/v1.0/media/upload" -F "media_file=@/path/to/test.wav" -F "type=audio" -F "custom_id=SampleAudio"
Response
{
"media_url": "lt://MEDIAID",
"status": "success"
}
Save the returned media_url — you will use it in subsequent steps.
Step 2 - Enable Audio Injection on Your Session
Set the enableAudioInjection capability when creating your driver session.
- Java
- Python
- Node.js
DesiredCapabilities caps = new DesiredCapabilities();
caps.setCapability("enableAudioInjection", true);
caps.setCapability("media", "lt://MEDIA1234567890abcdef"); // optional — pre-set audio
desired_caps = {
"enableAudioInjection": True,
"media": "lt://MEDIA1234567890abcdef", # optional
# ... other capabilities
}
const capabilities = {
enableAudioInjection: true,
media: "lt://MEDIA1234567890abcdef", // optional
// ... other capabilities
};
Setting the media capability pre-injects the audio when the session starts. You can still use the lambda-audio-injection hook later to switch to a different file mid-session.
Step 3 - Inject and Control Audio with Lambda Hooks
Use the following hooks via driver.executeScript:
| Hook | Description |
|---|---|
lambda-audio-injection=<media_url> | Set the audio file to be injected |
lambda-audio-start | Start playing the injected audio into the device microphone |
lambda-audio-stop | Stop audio playback |
- Java
- Python
- Node.js
// 1. Set the audio file
driver.executeScript("lambda-audio-injection=lt://MEDIA1234567890abcdef");
// 2. Trigger the app's mic input (e.g., tap Record / Start Voice Search)
driver.findElement(AppiumBy.id("recordButton")).click();
// 3. Start audio playback — the app receives the file as live mic input
driver.executeScript("lambda-audio-start");
// ... wait for the app to finish capturing ...
// 4. Stop audio playback
driver.executeScript("lambda-audio-stop");
driver.execute_script("lambda-audio-injection=lt://MEDIA1234567890abcdef")
driver.find_element(AppiumBy.ID, "recordButton").click()
driver.execute_script("lambda-audio-start")
# ...
driver.execute_script("lambda-audio-stop")
await driver.executeScript("lambda-audio-injection=lt://MEDIA1234567890abcdef");
await driver.findElement(By.id("recordButton")).click();
await driver.executeScript("lambda-audio-start");
// ...
await driver.executeScript("lambda-audio-stop");
Execution Rules
- Audio must be injected before triggering the microphone in the app. The last injected audio is the active input.
- The session must be created with
enableAudioInjection: true. Hooks called without the capability return HTTP 403 Forbidden. - Calling
lambda-audio-startbefore any file has been injected returns HTTP 400 withAUDIO_INJECTION_MEDIA_FILE_NOT_PROVIDED_ERROR. - Multiple injections in the same session — the last injected audio is used on the next
lambda-audio-start. - The app must be granted microphone permission. Audio Injection does not bypass permission prompts.
Best Practices
- Keep audio files short (under 5 minutes) for predictable timing.
- Use 16 kHz mono PCM-encoded MP3 or WAV for best compatibility across devices.
- Inject the audio file once at session start, then call
lambda-audio-start/lambda-audio-stoparound your test steps for precise control. - For voice-recognition tests, allow the device 1-2 seconds of silence before injecting speech to let the recognizer initialize.
FAQs
Q. Can I use Audio Injection with my own automation framework?
Yes — Audio Injection is a server-side feature controlled entirely by capabilities and executeScript hooks. It works with any Appium- or Selenium-compatible framework.
Q. Does Audio Injection work in parallel test runs?
Yes — each session has its own isolated injection pipeline. Multiple parallel sessions can inject different audio files simultaneously without interference.
Q. What audio formats give the best results?
16 kHz mono MP3 or WAV files give the most consistent results across both Android and iOS. iOS internally upscales to 48 kHz; Android operates natively at 16 kHz.
Q. My speech-to-text app isn't picking up the injected audio. What's happening?
Confirm:
enableAudioInjection: trueis set on the session.lambda-audio-injection=<url>was called beforelambda-audio-start.- The app has been granted microphone permission.
- Some apps (e.g., Google Recorder on Pixel) use privileged hardware audio paths that bypass standard injection — use a different recorder app to verify.
Q. Can I switch audio files mid-session?
Yes — call lambda-audio-injection=<new_url> followed by lambda-audio-start. The new file replaces the previous one immediately.
Related Features
- Camera Image Injection — Inject images into the device camera
- Video Injection — Inject videos into the device camera
- Biometric Authentication — Simulate fingerprint/face authentication
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