CoreFit MD

What it does

Playback

Every set opens on the movement

Each exercise carries a clip window. The player starts at 0:30, re-seeks on ready, and a watchdog pulls it back if playback ever passes the window end — so fifty seconds of plank keeps showing the plank. If the clip is blocked, dead or you are offline, a still of the same move takes its place — so the workout becomes a slideshow rather than a black box.

Programme

Six weeks that get harder

Work intervals climb from 45 to 60 seconds with a deload in week four, driven by how many sessions you have actually logged. Warm-up and cool-down bracket every session.

Privacy

Nothing leaves the device

History, streaks, clip windows and settings live in this browser. Export a JSON backup, print a one-page summary, or wipe it by clearing site data.

With the network off

Every move also has a still of its own — 1280×720, watermarked, a hundred kilobytes. No connection, no licensing problem, no black box.

Forearm plank demonstration still — **Plank**anti-extension

Dead bug demonstration still — **Dead bug**anti-extension

Bird dog demonstration still — **Bird dog**anti-rotation

Bicycle crunch demonstration still — **Bicycle**rotation

Hollow body hold demonstration still — **Hollow hold**anti-extension

These are generated for this app, not frames from the videos — the clips are other people's work and are only ever embedded, with the channel credited under the player and listed in the app's Sources and credits.

What it refuses to do

✕
No account, no sign-in, no sync There is no server to sync with. A backup file is the whole sync story.
✕
No analytics, no third-party scripts The only network request the app makes is the video embed. Set Clip source to Local and there are none at all.
✕
No streak mechanics that punish rest One missed day is forgiven anywhere in the chain. Two in a row end it.
✕
No medical claims It screens for contraindications and tells you to stop if a move hurts. It is a training aid, not advice.

The rule

Why the first frame is the one that matters.

0:00 — 1:20 of source videoplayback window

Most workout apps embed a video and press play. The clip begins with a channel ident, then a presenter explaining the move, then the movement — by which point you have lost fifteen seconds of a fifty-second set.

Here the clip window is data: start 0:30, end 0:55, editable per exercise. The player is created with that start, seeked again the moment it is ready, and re-seeked whenever playback passes the end. During each rest interval the next clip is preloaded, so the following set opens instantly.

If an embed is blocked, dead, or you are offline, the session still runs — a still of the movement takes the video's place, the channel is still credited, and the timer never notices.

The numbers

5moves

6:15week 1, full session

0:30clip in-point

3languages

0runtime deps

1.4MB, whole app

Run it

# any static server works
git clone https://github.com/drsamonline/corefit-md
cd corefit-md
python3 -m http.server 8080
# then open localhost:8080/docs/

# the app alone, from disk:
open docs/play/index.html

# regenerate the assets in this repo
python3 scripts/badges.py
python3 scripts/figures.py
bash scripts/shot.sh . app

docs/index.html       this page
docs/play/            the app
  index.html            markup only
  assets/css/app.css    the design system
  assets/js/            config · data · store
                        i18n · video · session
                        ui · main
  assets/i18n/          en · hi · gu
  assets/media/         10 stills, watermarked
  assets/demo/          10 SVG figures (fallback)
  sw.js                 offline shell
scripts/              badges and screenshots
BACKLOG.md            what is next, and what is refused

CoreFit MD Five minutes, and the clip starts where the movement starts.

This is the app itself, not a picture of it.