User Camera Access: Request and Manage Browser Camera Permissions Safely

Question

## Problem

Implement a module that requests camera access via the browser's MediaDevices API, handles permission denial gracefully, streams video to a `<video>` element, and cleanly releases the camera when no longer needed.

```js
class CameraAccessManager {
  constructor(videoElement) {
    this.video = videoElement;
    this.stream = null;
  }

async requestAccess(constraints = { video: true }) { ... }
  async switchCamera(deviceId) { ... }
  release() { ... }  // stops all tracks
  captureFrame() { ... }  // returns ImageData from current frame
}
```

**Requirement:** If the user denies permission, show a clear error message. If multiple cameras exist, expose a list and allow switching.

## Follow-ups

1. What is the difference between `getUserMedia` constraints `facingMode: 'environment'` and specifying a `deviceId`?
2. How do you enumerate available cameras before requesting access, and what limitation applies?
3. What cleanup is required to ensure the browser's camera indicator light turns off?
4. How would you handle the case where the user revokes camera permission while the stream is active?

User Camera Access: Request and Manage Browser Camera Permissions Safely

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