repcast.

A workout coach for Amazon Fire TV

The coach on your TV that sees every rep.

Prop up the phone you already own. It watches your form; the TV counts every rep, tells you what to fix in a coach's voice, and never counts a rep that doesn't count.

See how it works Read the code
  • Any Fire TV — even the 1 GB stick
  • Your phone — nothing to install
  • 2 metres of floor
RepCast on a Fire TV: live video of a lifter at the bottom of a squat in a gym, an orange skeleton drawn on him, the rep count and the coach's line
The phone camera page: the same lifter at the bottom of a squat with the skeleton, 6 of 12, knee at 70°, and “Good rep”.
Phone → TV over your Wi-Fi. Never the cloud.
Clean Good depth. No rep Not low enough — that one doesn't count Note Push your knees out No rep That's a lunge — this set is squats Coach Step back a little, so I can see all of you. No rep Feet wider — this set is sumo squats Clean That's it — smooth. No rep That was a full squat — this set is half squats Note Chest up the whole way down Coach Rest. Next: squats, set 2.

An honest coach

Every rep judged. None of them given away.

A rep only counts when it's real. When it doesn't, RepCast says why — and it knows a lunge from a squat, a reverse lunge from a forward one, and a step jack from a jumping jack.

Clean Good depth.

Deep enough, knees out, chest up. Counted, and coloured orange on your receipt.

Counted, with a note Push your knees out.

The rep counts, and the coach tells you the one thing to fix on the next one.

No rep That's a lunge — this set is squats.

Not low enough, the wrong move, or you wandered off your spot: it doesn't count, and you hear why.

Tested in a real gym

Real lifters, real reps — judged by the same code that runs on your phone.

Squats, from the frontEvery rep counted, every one clean.
A second lifterFirst rep too shallow: counted, with “go a little lower”.
Split squats, from the sideEvery rep counted — side-on works too.
Same clip, as a squat setNone counted: “That's a split squat — this set is squats.”
12moves the camera checks, each with an easier version
3camera angles it judges from: front, 45° and the side
72tests in the open-source rep engine
1 GBFire TV Stick it was built and measured on
117coach lines, recorded with Amazon Polly

How it works

Pick a move. Scan. Train.

No account, no app on your phone, no camera to buy. The TV leads; the phone just watches.

The TV's pairing screen: a QR code and a 4-digit code, the phone connected, the live picture with head, hips, knees and feet ticked, and the set about to start.

Pick a move on the TV

Squats, lunges, jumping jacks, push-ups or glute bridges. The TV shows a QR code and a 4-digit code.

The phone page tracking a squat.

Scan it with your phone

The camera page opens in the browser. Prop the phone at hip height, about 2.5 m away, turned 45° to you.

The live set on the TV with the person's video and skeleton.

Train — it starts itself

When the phone can see you, a 5-second countdown starts the set. Reps, rests and the coach's voice come from the TV.

Workout analysis on the TV: all 36 counted, 100% clean, deepest knee angle 60°, a bar for every attempt, form breakdown, a trend against earlier sessions and Amazon Nova's coach note.

After every move

See exactly how it went.

  • A bar for every attempt, by set: how deep, and whether it counted.
  • What the camera spotted most, and how today compares with last time.
  • A coach's note from Amazon Nova on Amazon Bedrock, written from your numbers only.
Progress on the TV: a year of training as a calendar of squares, streaks, clean-form trend and the moves trained most.

For everyone in the house

A year at a glance.

  • One square per day, darker the more reps you did.
  • Streaks, clean form over time and the moves you train most.
  • A profile per person, kept on the TV. No sign-in.
When the live picture can't reach the TV: the 3D trainer shows the move, a notice explains the phone and TV need the same Wi-Fi, and the person's outline is shown in a corner.

Built for real living rooms

Even when the picture can't get through.

  • On guest or office Wi-Fi the video can't cross — the 3D trainer shows the move instead, and your outline still follows you.
  • Reps still count, and the coach still talks.
  • No camera on the TV? Follow along with the trainer instead, on a steady beat.

Follow along · no camera needed

A 3D trainer for all 17 moves, in time with the coach's count.

SquatsHips back, chest up.
Jumping jacksOn the beat, counted for you.
Push-upsSide-on, so you see the line.
Forearm plankHolds are timed, not counted.

Private by design

Your picture never leaves your home.

Body tracking runs on your phone. The video goes straight to your TV. Only numbers ever reach the internet. Read the privacy policy.

Your phone

Finds your body in each frame and judges every rep, right in the browser.

live video,
home Wi-Fi only

Your Fire TV

Shows you, keeps the count, speaks, and keeps everyone's history — on the TV.

rep numbers only
no video, ever

AWS

Links phone and TV with a code that expires in 2 hours, and writes the AI note if you ask for one.

Open source

The rep engine is yours to use.

repcast-movement turns pose points into reps, holds and honest form feedback. MIT licensed, 72 tests, exercises defined as plain data — add your own without new code.

Amazon Fire TV React Native for TV Expo TypeScript MediaPipe Pose WebRTC Vite Vitest GitHub Actions AWS AppSync Events Amazon API Gateway AWS Lambda Amazon DynamoDB Amazon Polly Amazon Bedrock · Nova AWS SAM · CloudFormation 
import { RepDetector, squat } from 'repcast-movement';

const detector = new RepDetector(squat);

// Every video frame, from MediaPipe:
const update = detector.update({
  t: performance.now(),
  landmarks: result.landmarks[0],
});

if (update.rep) {
  update.rep.verdict; // 'no-rep'
  update.rep.cues;    // ["Not deep enough"]
}

Built for Build, Ship, Shape — the Amazon Developer Hackathon 2026

Every rep, seen.

Get RepCast on GitHub Open the phone camera page