Mock Video Injection on Web Automation (Selenium/Chromium)

Inject a custom video file as a fake camera feed in Chromium-based Selenium tests on TestMu AI. This is useful for testing WebRTC, video conferencing, KYC or identity verification, and any flow that calls getUserMedia().

How It Works

---

Upload a video file, pre-load it onto the test VM, and pass Chrome flags to use it as a fake camera device.

1. Upload your .mjpeg or .y4m video file to TestMu AI using the web automation user-files API.
2. Pre-load the file onto the test VM using the lambda:userFiles capability.
3. Pass Chrome flags to use the uploaded file as a fake camera device.

Chrome treats the file as a looping camera feed, so any getUserMedia({ video: true }) call receives frames from your file instead of a real camera.

Prerequisites

---

Verify the following before configuring mock video injection.

1. Get a TestMu AI account with Web Automation access from your dashboard.
2. Prepare a .mjpeg video file such as sample_640x360.mjpeg (recommended resolution: 640x360 or 1280x720; Chrome also supports .y4m format).
3. Set TestMu AI credentials as LT_USERNAME and LT_ACCESS_KEY.

Step 1: Upload the Video File

---

Upload your .mjpeg file using the web automation user-files API.

cURL

Verified

curl -X POST \
  "https://api.lambdatest.com/automation/api/v1/user-files" \
  -u "$LT_USERNAME:$LT_ACCESS_KEY" \
  -F "files=@/path/to/sample_640x360.mjpeg"

Response

Verified

{
  "status": "success",
  "data": [
    {
      "error": "",
      "message": "File have been uploaded successfully to our lambda storage",
      "key": "sample_640x360.mjpeg"
    }
  ]
}

note

Limits: maximum 20 MB per upload and maximum 150 files per organization.

The /mfs/v1.0/media/upload endpoint is for mobile and app automation. For web automation, use /automation/api/v1/user-files.

Step 2: Configure Selenium Capabilities

---

Add the video file and Chrome flags to your Selenium capabilities configuration.

Java (Selenium 4, W3C)

Verified

import org.openqa.selenium.chrome.ChromeOptions;
import org.openqa.selenium.remote.RemoteWebDriver;
import java.net.URL;
import java.util.*;

ChromeOptions options = new ChromeOptions();

options.addArguments(
    "--use-fake-ui-for-media-stream",
    "--use-fake-device-for-media-stream",
    "--use-file-for-fake-video-capture=/home/ltuser/Downloads/sample_640x360.mjpeg"
);

HashSet<String> userFiles = new HashSet<>();
userFiles.add("sample_640x360.mjpeg");

HashMap<String, Object> ltOptions = new HashMap<>();
ltOptions.put("platform", "Linux");
ltOptions.put("build", "Mock Video Injection Test");
ltOptions.put("name", "Fake Camera Feed Test");
ltOptions.put("video", true);
ltOptions.put("w3c", true);

options.setCapability("LT:Options", ltOptions);
options.setCapability("lambda:userFiles", userFiles);

RemoteWebDriver driver = new RemoteWebDriver(
    new URL("https://" + LT_USERNAME + ":" + LT_ACCESS_KEY + "@hub.lambdatest.com/wd/hub"),
    options
);

Python

Verified

from selenium import webdriver

options = webdriver.ChromeOptions()
options.add_argument("--use-fake-ui-for-media-stream")
options.add_argument("--use-fake-device-for-media-stream")
options.add_argument("--use-file-for-fake-video-capture=/home/ltuser/Downloads/sample_640x360.mjpeg")

lt_options = {
    "platform": "Linux",
    "build": "Mock Video Injection Test",
    "name": "Fake Camera Feed Test",
    "video": True,
    "w3c": True,
}

options.set_capability("LT:Options", lt_options)
options.set_capability("lambda:userFiles", ["sample_640x360.mjpeg"])

driver = webdriver.Remote(
    command_executor=f"https://{LT_USERNAME}:{LT_ACCESS_KEY}@hub.lambdatest.com/wd/hub",
    options=options,
)

JavaScript (WebDriverIO or raw WebDriver)

Verified

const capabilities = {
  browserName: "Chrome",
  browserVersion: "latest",
  platformName: "Linux",
  "LT:Options": {
    platform: "Linux",
    build: "Mock Video Injection Test",
    name: "Fake Camera Feed Test",
    video: true,
    w3c: true,
  },
  "lambda:userFiles": ["sample_640x360.mjpeg"],
  "goog:chromeOptions": {
    args: [
      "--use-fake-ui-for-media-stream",
      "--use-fake-device-for-media-stream",
      "--use-file-for-fake-video-capture=/home/ltuser/Downloads/sample_640x360.mjpeg",
      "--no-sandbox",
      "--disable-gpu",
    ],
  },
};

Step 3: Verify the Video Feed in Your Test

---

Navigate to a page that requests camera access and confirm the fake stream is active.

After the session starts, navigate to a page that requests camera access and confirm the fake stream is being used.

Verified

driver.get("https://www.lambdatest.com/selenium-playground/webrtc-video");

// Or open your application's camera page
driver.get("https://your-app.com/video-call");

Boolean isPlaying = (Boolean) driver.executeScript(
    "const video = document.querySelector('video');" +
    "return video && !video.paused && video.readyState >= 2;"
);

File Paths by OS

---

The lambda:userFiles capability places files in these directories.

Platform	File Path
Linux	/home/ltuser/Downloads/sample_640x360.mjpeg
Windows	C:\\Users\\ltuser\\Downloads\\sample_640x360.mjpeg
macOS	/Users/ltuser/Downloads/sample_640x360.mjpeg

Adjust the --use-file-for-fake-video-capture path to match your target platform.

Chrome Flags Reference

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The following Chrome flags control fake media device behavior.

Flag	Purpose
--use-fake-ui-for-media-stream	Auto-grants getUserMedia() permission without a popup
--use-fake-device-for-media-stream	Replaces real camera and microphone hardware with fake devices
--use-file-for-fake-video-capture=<path>	Uses the specified file as the fake camera feed
--use-file-for-fake-audio-capture=<path>	Uses the specified file as fake microphone input (.wav format)

Troubleshooting

---

Refer to the following table for common issues and solutions.

Issue	Solution
Black or empty video feed	Verify the file name in lambda:userFiles matches exactly, including case
Permission popup still appears	Confirm --use-fake-ui-for-media-stream is set
File not found on VM	Check the OS-specific path; if needed, use driver.executeScript("lambda-files-download=sample_640x360.mjpeg") as a fallback
Video not looping	Chrome loops .mjpeg files automatically; .y4m files also loop by default
Wrong resolution	Use a file resolution that matches your app expectations; 640x360 is a safe default
Windows path errors	Use escaped backslashes: C:\\Users\\ltuser\\Downloads\\sample_640x360.mjpeg
macOS video does not render	This is a known Chrome limitation; use Linux when visual verification is required