LMS-2242 Production log

AI concept lecture video v2 — interactive player with linked review (follow-up to LMS-2241)

Deliverables

Item	Location
Web player link	https://claude.ai/artifact/QxEPQfBTKgB6ipBQptNZyX (shared within the W Labs organization)
Script (subtitles + TTS input + checkpoint problems)	https://bitbucket.org/devmeoi06/aiv/src/main/docs/LMS-2242_script_ko.md
Lesson data (reusable template)	`lessons/schema.ts` (format), `lessons/linear-function-equation/lesson.ko.json` (content)
Source code	https://bitbucket.org/devmeoi06/aiv — `src/lesson-v2/` (lesson engine), `src/lesson/Senior.tsx` (avatar), `player/` (web player), `scripts/` (voice, checking, script and publishing scripts)
Production log	https://bitbucket.org/devmeoi06/aiv/src/main/docs/LMS-2242_production-log_en.md (this file), https://bitbucket.org/devmeoi06/aiv/src/main/docs/LMS-2242_production-log_ko.md (Korean)

Unit: Linear functions and graphs — Finding the equation of a linear function (the sub-unit after last lesson's "slope and y-intercept")
Linked review: last lesson (slope, y-intercept) + Grade 7 direct proportion y = ax
Curriculum: 2022 revised curriculum [9수02-16], understanding and applying the properties of linear function graphs. ⚠️ Matched via a secondary source; confirm against the official NCIC text
Length: 6:24 (requirement 5–10 min ✅; excludes time paused at checkpoints)
Voice and subtitles: Korean narration + Korean subtitles ✅
Avatar: an original character drawn in code (male senior student). No real person's likeness ✅
Textbook copying: none. All examples and problems are newly written ✅

Acceptance criteria check

Criterion	Result
Working web player link, source code and script submitted	✅ Link, source and script ready (attaching and sharing still to do)
At least 2 checkpoint problems that block playback until answered	✅ 3 (1:44 multiple choice, 3:36 number input, 5:32 multiple choice)
Section timing 5% / 90% / 5%	✅ Measured 4.8% / 90.4% / 4.8%
Speed control keeps audio and subtitles in sync	✅ Tested at 0.75×, 1×, 1.25×, 1.5×, 2× (see below)
Zero math errors, confirmed by a Korean reviewer	⏳ Automated check passes — Korean reviewer needed
Tools, prompts, time and cost documented, compared with LMS-2241	✅ This document
No copied textbook content, no real person's likeness	✅

Lesson structure

Section shares are computed from the measured narration. The 2 s intro counts toward the review and the 4 s outro toward the summary.

Section	Content	Length	Share
Opening (linked review)	Last lesson's y = ax + b; Grade 7 direct proportion y = 2x → y = 2x + 2	18.4 s	4.8%
Main (concept + checkpoints)	① slope and y-intercept ② slope and one point (parallel lines) ③ two points (x- and y-intercepts), 3 checkpoints, comparing the three methods and checking answers	346.2 s	90.4%
Closing (key summary)	The three cases recapped, next lesson preview	18.5 s	4.8%

Interactive features and test results

Each was checked by running the player in a browser.

Feature	Behavior	Test result
Checkpoint stop	Stops exactly at the problem and shows the question card	✅ Stopped exactly at 1:44 and 3:36, audio silent
Skip blocking	Space bar, progress-bar click and play button are all blocked	✅ All three stayed at 1:44
Instant feedback	Correct → explanation / wrong → hint / 2 wrong → answer and explanation revealed	✅ All three cases confirmed
Number-input problem	Typed number; the "−" sign used in the subtitles is also accepted	✅ "2" → hint, "−2" → correct
Continue	Resumes into the solution narration	✅ (confirmed after fixing one bug)
Speed control	0.75×–2× buttons	✅ 2×: 9 s of video in 4.2 s; 0.75×: 6 s of video in 8 s
Audio/subtitle sync	Subtitles and mouth follow the frame, so they match at any speed	✅ At 2×, the subtitle matched the playing narration in 6 of 6 samples; pitch preserved
Mobile	No sideways scrolling at 375 px	✅ (subtitles inside the video look small on phones)

CEO feedback, round 2

Feedback	Cause	Fix
"No sound for the first 1–2 seconds"	Each line's audio file was only loaded when that line started, so its first syllables were lost while it loaded	Each voice's narration and chimes are mixed into one continuous track, loaded once (`scripts/lesson-track.ts`). First syllables play; checkpoint stop/resume stays in sync (stopped at 106.6 s → after resume audio 109.5 s / video 1:50)
"A bright, high-pitched female instructor voice"	—	Full narration added in `ko-KR-SunHiNeural`, rate +10%, pitch +15%. Its ~1 s stall after a mid-sentence "!" is fixed by reading it as a comma. Length 6:34, split 4.9% / 90.4% / 4.8%
(added) Avatar and theme selector	—	Presenter buttons above the player (male senior = Hyunsu / female teacher = SunHi with the teacher avatar) and theme buttons (classic, chalkboard, night, pastel). Changing voice restarts the lesson; changing theme keeps the position

Tools

Step	Tool	Notes
Script, lesson data, avatar, player code	Claude Code (Claude Opus 5.5)	All AI-written
Voice	Microsoft Edge neural TTS, `ko-KR-HyunsuMultilingualNeural`, rate +10%, pitch +4%	Picked from 3 samples
Lip sync	ffmpeg extracts voice loudness → avatar mouth shapes
Lesson engine	Remotion 4.0.535 + @remotion/player	Draws the lesson straight from its JSON
Web player	React 19, Vite 6.3.5	Checkpoints, feedback, speed control
Hosting	Claude Artifact (private link)	For the pilot
Math check	Custom checker `scripts/lesson-check.mjs`	Verifies every example, point, slope and answer by calculation

Prompts

User → Claude Code prompts (verbatim, in order):

Currently I have an in progress related to the continuation of this ticket, please retrieve that ticket and analyze it. → LMS-2242 analysis
Go with your recommended defaults: topic = 일차함수의 식 구하기, review = 지난 시간 기울기·y절편 + 중1 정비례, host as a private Artifact link first, keep the illustrated avatar restyled as a friendly senior. Start with the lesson JSON template and script. → lesson template and script
Yes, generate 2-3 short voice samples of the friendly-senior persona (different Edge voices or settings) so I can pick one. → 3 voice samples
Use C (Hyunsu, young male senior) for the lesson. → voice chosen
Yes, restyle the avatar as a young male senior student to match the Hyunsu voice, then generate the full narration. → avatar and full narration
Yes, build the interactive web player: checkpoints that block playback, instant feedback, 0.75x-2.0x speed control with synced subtitles, using the new avatar and narration. → web player
Yes, publish the player as a private Artifact link. → published
CEO feedback relayed: no sound for the first 1–2 s, a bright high-pitched female instructor voice, plus I think let's add an avatar and theme selector? → continuous track, SunHi voice, presenter and theme selectors

Time

Step	Time
Ticket analysis, choosing defaults	~5 min
Lesson template and script, automated math check, section balancing	~20 min
3 voice samples	~3 min
Avatar + full narration (44 clips)	~10 min
Lesson engine + web player	~12 min
Browser testing, 2 bug fixes	~5 min
Publishing	~3 min
Total	~1 h (excluding time waiting on user replies)

Cost

Item	Cost
TTS (Edge neural TTS)	₩0
Remotion · @remotion/player (free license for small teams*)	₩0
React, Vite, ffmpeg, fonts	₩0
Hosting (Claude Artifact)	Within existing subscription
Claude Code usage	Within existing subscription (no extra charge)
Total	₩0 extra

* Remotion is free for companies with 3 or fewer employees; larger companies need a company license. The same applies to the player (@remotion/player).

Comparison with LMS-2241

	LMS-2241 (v1)	LMS-2242 (v2)
Deliverable	MP4 video	Web player (link)
Unit	Linear functions and graphs — slope and y-intercept	Finding the equation of a linear function (next sub-unit)
Length	4:27	6:24
Structure	Intro, explanation, summary (no ratio target)	Linked review 5% / main 90% / key summary 5% (measured 4.8 / 90.4 / 4.8)
Linked review	None	Last lesson + Grade 7 direct proportion
Learner participation	None (watch only)	3 checkpoints that block playback; correct / hint / explanation feedback
Speed control	None (depends on the video player)	0.75×–2× with audio and subtitles in sync
Voice	SunHi (female), polite teacher, rate −4%	Hyunsu (male), casual senior, rate +10%
Avatar	Female teacher	Male senior student (hoodie)
Lesson content format	Each scene written as code	JSON template; a new lesson is a new JSON file
Math check	Checked by AI by eye	Checker script verifies every example, point and answer by calculation
Time	First Korean video ~30 min (~3 h 10 min with variants)	~1 h (including the player)
Cost	₩0 extra	₩0 extra
Making the next lesson	Write new scene code	Write JSON → `lesson-check` → `lesson-tts` → build (engine and player reused)

Math check (automated check passes — Korean reviewer needed)

Result of node scripts/lesson-check.mjs lessons/linear-function-equation/lesson.ko.json:

Slope 3, y-intercept −2 → y = 3x − 2 ✔
Graph through (0, −1), right 1 / up 2 → y = 2x − 1 ✔
Checkpoint 1: slope −2, y-intercept 5 → y = −2x + 5 ✔
Slope 2 through (1, 5) → y = 2x + 3 ✔
Slope −3 through (2, −1) → y = −3x + 5 ✔
Parallel to y = 3x through (2, 1) → y = 3x − 5 ✔
Checkpoint 2: slope 3 through (2, 4) → b = −2 ✔
Through (1, 3) and (3, 7) → y = 2x + 1 ✔
Through (−1, 4) and (1, 0) → y = −2x + 2 ✔
x-intercept 2, y-intercept 4 → y = −2x + 4 ✔
Checkpoint 3: through (−1, 1) and (2, 7) → y = 2x + 3 ✔ (each of the 3 wrong choices misses at least one of the points)
Every point on a graph lies on a drawn line, and every run/rise label matches the actual coordinate difference ✔

Open items

Korean reviewer confirms zero math errors — against LMS-2242_script_ko.md
Curriculum check — confirm [9수02-16] against the official NCIC text
For production: host the player in the W Labs LMS, licensed TTS (e.g. Azure Speech), Remotion company license
Possible improvement: subtitles look small on phones → show them in the player UI below the video on mobile