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This question is commonly asked for Software Engineer candidates at Verkada during technical interviews.

Implement a JavaScript frame player controller

Q: Implement a JavaScript frame player controller

This question evaluates a candidate's understanding of precise time-based scheduling, browser timer APIs, closure-based state encapsulation, and playback control logic in JavaScript for a frame-by-frame media controller.

Implement a frame-by-frame browser media controller with drift-proof scheduling

Context

You are given a skeleton for a frame-by-frame browser media player. Assume you have:

A renderFrame(index) callback that draws frame index onto the UI (e.g., a canvas or an image element).
A known total number of frames: frameCount.

Your job is to implement a JavaScript controller that manages playback precisely by frames.

Requirements

Implement a controller that:

Jumps to any frame by index.
Starts and pauses autoplay at a configurable frames-per-second (FPS).
Exposes methods:
- play()
- pause()
- seek(frameIndex)
- setFPS(fps)
- currentFrame()
- isPlaying()
Uses setTimeout or setInterval correctly to schedule frames, handles timer drift, and prevents overlapping timers.
Encapsulates internal state via closures and cleans up timers/listeners to avoid memory leaks.

Deliverables

A working design and explanation of your time-scheduling strategy.
A comparison of setTimeout vs setInterval (and optionally requestAnimationFrame) for this use case.
Pseudocode or tests showing expected behavior and edge cases.

Context

You are given a skeleton for a frame-by-frame browser media player. Assume you have:

A renderFrame(index) callback that draws frame index onto the UI (e.g., a canvas or an image element).

A known total number of frames: frameCount.

Your job is to implement a JavaScript controller that manages playback precisely by frames.

Requirements

Implement a controller that:

Jumps to any frame by index.

Starts and pauses autoplay at a configurable frames-per-second (FPS).

Exposes methods:

play()
pause()
seek(frameIndex)
setFPS(fps)
currentFrame()
isPlaying()

Uses setTimeout or setInterval correctly to schedule frames, handles timer drift, and prevents overlapping timers.

Encapsulates internal state via closures and cleans up timers/listeners to avoid memory leaks.

Implement a JavaScript frame player controller

Quick Overview

Implement a frame-by-frame browser media controller with drift-proof scheduling

Context

Requirements

Deliverables

Solution

Submit Your Answer to Earn 20XP

Implement a JavaScript frame player controller

Quick Overview

Implement a frame-by-frame browser media controller with drift-proof scheduling

Context

Requirements

Deliverables

Solution

Submit Your Answer to Earn 20XP