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100ms
100ms Software Engineer Interview Guide 2026
Complete 100ms Software Engineer interview guide. Prepare for WebRTC and live video infrastructure questions, practical coding rounds, SDK engineering, and the fast-moving culture of a video API startup.
5 min read
Updated Sep 2026
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100ms builds live video and audio infrastructure, SDKs and APIs that let apps embed conferencing and streaming rooms, and its Software Engineer loop is a startup-fast, technically deep process. Expect a recruiter or founder screen, a coding round at LeetCode medium with practical leanings, a systems round that dives into realtime media, WebRTC concepts, SFU architecture, latency and quality trade-offs, or SDK design for mobile and web tracks, and a culture round with founders or senior engineers. The team came from building video at scale and interviews for depth plus velocity, small teams own large surface and ship quickly. Media experience is a plus, not a prerequisite, strong systems fundamentals and genuine curiosity carry the loop. Timelines are quick, often 2 to 4 weeks.
2-4 weeks
Sample Questions
Design a group video calling service for 50 participants
SFU architecture, simulcast layer selection per subscriber, room state management, regional media servers, and reconnection with continuity.
Why can't a 10-person call use peer-to-peer mesh?
Upload bandwidth arithmetic, N-1 encoded streams per client, leading to the SFU model and its per-subscriber forwarding economics.
A user's video freezes while audio continues. Diagnose it
Reason across packet loss on the video stream, keyframe waits, layer switching, and client decode issues, a realistic media debugging scenario.
Design the SDK API for joining a room and rendering peers
Developer-experience design, minimal join flow, reactive peer and track events, error surfaces, and hiding platform lifecycle complexity.
Implement a jitter buffer for audio packets
Reorder out-of-sequence packets under a latency budget, handle gaps and late arrivals, and justify the buffer-depth trade-off.
Tell me about the most ambiguous project you drove alone
Startup ownership check, scoping without guidance, deciding under uncertainty, shipping, and iterating on real feedback.
About the Interview Process
100ms interviews are run by senior engineers and founders who built video systems at scale before starting the company, and they calibrate for both depth and speed. Coding rounds check fundamentals efficiently; domain rounds teach as they test, interviewers happily explain media concepts and grade how quickly you reason with new information; culture rounds assess ownership appetite for a startup where engineers carry meaningful surface alone. The loop moves fast and communicates directly.
Recruiter / Founder Screen
Background, motivation, and mutual pitch. At startup scale this round carries real evaluative weight, come prepared with why 100ms specifically.
Coding Round
One or two problems at LeetCode medium, often with practical texture, buffering, scheduling, stream processing, graded on correctness and speed of clean execution.
Systems / Domain Round
Design a group video call service or component, SFU forwarding, quality adaptation, room state, reconnection, with interviewers supplying media context as needed and probing your reasoning.
SDK or Platform Deep Dive
Track-dependent depth, mobile lifecycle and permissions handling for SDK roles, Go or Node service design for backend roles, or browser media APIs for web roles.
Culture & Founder Round
Ownership stories, pace preferences, and ambition alignment with founders or senior leadership, an honest two-way conversation about startup fit.
Timeline
2 to 4 weeks, sometimes faster. Startup decision-making means offers can follow finals within days.
Tips
Reason from first principles when you hit unfamiliar media territory, interviewers reward candidates who derive why jitter buffers exist rather than bluffing.
Quantify latency budgets in design answers, interactive video needs roughly 200 milliseconds end to end, and knowing that number frames every trade-off.
For SDK questions, champion the developer experience, a video SDK's API clarity is the product, and caring about it visibly matters.
Ask the founders about roadmap and market directly, they engage candidly, and thoughtful questions register as signal.
What they test
100ms's technical rounds center on realtime media systems, and the SFU is the architectural heart. Strong candidates can explain why a five-person call cannot be a full mesh at scale, how a selective forwarding unit routes each publisher's simulcast layers to subscribers based on their bandwidth and view layout, and what happens when a subscriber's network degrades mid-call, layer downgrade, jitter buffer stretch, and eventually audio-only fallback. None of this requires prior media work, interviewers supply context, but you must reason crisply with it once given.
The quality axis is latency versus resilience. Interactive conversation tolerates roughly 200 milliseconds end to end, which forces UDP transport, shallow buffers, and loss recovery that cannot wait for retransmission round trips, hence FEC and reference-frame tricks. Candidates who internalize that single constraint can derive most right answers in the domain round from first principles.
SDKs, scale, and startup surface
Half of 100ms's engineering is developer experience, SDKs for Android, iOS, React Native, Flutter, and web that wrap brutal platform complexity, camera lifecycles, permission flows, backgrounding, Bluetooth audio routing, into APIs a developer integrates in an afternoon. SDK-track interviews probe platform depth and API taste, design the room-join API, handle a mid-call device rotation, keep the SDK small and the errors actionable.
Backend tracks own the media servers, room orchestration, recording pipelines, and global deployment that keep calls flowing, Go-heavy services where a bug is a thousand simultaneous dropped calls. Across tracks, the startup reality is the pitch and the filter, small teams, direct founder access, meaningful equity, and ownership that big-company engineers wait years for, offered at Bangalore-centered compensation with the intensity that stage implies.
Leveling & Compensation
| Level | Title | YoE | Total Comp (USD/yr) |
|---|---|---|---|
SDE-2 | Software Engineer II | 2-5 yrs | $30k - $65k |
SDE-3 | Senior Software Engineer | 5-8 yrs | $50k - $95k |
Staff | Staff Engineer / Tech Lead | 8+ yrs | $75k - $140k |
Software Engineer II
Owns features across a service or SDK, ships quickly with quality judgment, and grows toward independent surface ownership.
Senior Software Engineer
Owns a platform area, media, SDK, or infrastructure, drives its design, and mentors while carrying startup-scale delivery.
Staff Engineer / Tech Lead
Sets technical direction across the platform, owns the hardest realtime problems, and multiplies the team through design and review.
How to Stand Out
Behavioral Focus Areas
Velocity: startup pace with small teams and large ownership
Depth: infrastructure customers build on demands real engineering
Ownership: features go from design to production with your name on them
Pragmatism: shipping the 80% that matters over polishing the 20%
Curiosity: media engineering rewards people who enjoy hard rabbit holes
1.
Learn WebRTC's architecture at a working level, peer connections, SDP negotiation, ICE with STUN and TURN, and why group calls need an SFU rather than mesh.
2.
Understand the SFU model, selective forwarding, simulcast layers, and how servers pick quality per subscriber under bandwidth constraints.
3.
Review networking fundamentals, UDP versus TCP for media, jitter buffers, packet loss recovery with NACK and FEC, and congestion control at a conceptual level.
4.
Practice LeetCode mediums, coding rounds are real, arrays, heaps, and concurrency-flavored problems appear.
5.
For SDK tracks, prepare platform depth, Android and iOS lifecycle handling, web browser quirks, and API design developers will love.
6.
Show shipping energy, concrete stories of building fast and owning outcomes fit the company's stage.
Related Courses
Recommended Resources
FAQ
Do I need WebRTC experience?
No, and most successful candidates arrive without it. Interviewers teach the media context and grade reasoning speed. That said, a weekend with WebRTC for the Curious and an SFU explainer converts you from learning live to confirming live, a meaningful edge worth the hours.
Where is the team and is remote possible?
100ms is India-centered with its core in Bangalore, and hires primarily in Indian time zones with hybrid or remote flexibility varying by role. Compensation bands here reflect the India market, with equity as a significant component at startup stage.
How does this compare to interviewing at Agora or Twilio?
The domain overlaps, realtime media infrastructure, while 100ms's loop is faster, more founder-involved, and weighted toward ownership fit. Larger incumbents run more standardized big-company processes; preparation for one substantially covers the other technically.
What is the honest startup risk?
Standard early-stage math, equity may become significant or may not, priorities shift quickly, and intensity is real. In exchange come rare ownership, direct work with founders who know the domain deeply, and infrastructure engineering experience that transfers anywhere. Ask about runway and revenue directly, founders answer.
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