# Demo Video > Demo video - Skill: `indrasvat/demo-video` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add indrasvat/demo-video` - Raw SKILL.md: https://api.skillmd.com/api/skills/indrasvat/demo-video/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Coding & Dev Tools - Author: indrasvat (https://skillmd.com/u/indrasvat) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/indrasvat/demo-video --- # Demo video A screenshot proves a state. A video proves a *transition* — the thing working, then not working. That is the only reason to make one. ## The rule that decides whether it is worth anything **Record the product's own UI. Never record a harness narrating itself.** The first cut of this on shux #107 was a script printing `marker visible: False` and `RESULT: PANE DEAD` in colour. Every fact in it was true and it demonstrated nothing — the reviewer's response was "all I see is commands and supposed outputs saying failed or passed". The rebuild attached a real client to a real session and let the reviewer watch a counter stop. Same bug, same binaries, completely different evidence. If your recording would still make sense with the product replaced by `echo`, it is a log with colours. ## Make the failure visible A broken thing and a working thing often look identical in a still frame. Give the recording **continuous motion that stops**: - run a ticking counter in the component under test (`n=0; while :; do n=$((n+1)); printf 'tick %04d\n' $n; sleep 0.5; done`) - a frozen counter reads as broken instantly, with no narration - keep some *other* part of the UI alive (a status bar) so "the app died" and "this component died" are visually distinct — that distinction is usually the finding **Label inside the content**, not as a post-hoc overlay: bake `BEFORE ` into the ticking line itself. A caption added later can drift from the footage it labels. ## Capture Prefer VHS: it drives a real terminal emulator and writes MP4 directly, so there is no frame pipeline to get wrong. See `vhs.md` for tape syntax, the root/sandbox failure, and the traps that cost time. No browser available → `vhs.md` also covers the fallback: record the PTY with timings, replay through the app's own renderer, `ffmpeg` the frames. More moving parts, but it renders authentic output and needs nothing but a PTY. Triggering a state change the recorder cannot perform (VHS cannot resize mid-tape): drive it **out of band** — start a background helper during the hidden setup that acts on the app at a known offset. Verify the trigger works on its own first; debugging a silent trigger through a video is miserable. ## Verify before you believe it Every one of these has produced a green-looking result that proved nothing: 1. **Extract frames from the ENCODED file and look at them.** Not the source frames — the `.mp4`. `ffmpeg -ss -i out.mp4 -frames:v 1 f.png`, then actually open them. 2. **Check the video is not blank.** Two recordings that both end with the program quitting compare byte-identical and are both empty. Assert on content — a frame with under ~20 non-blank cells is not evidence. 3. **Check duration and dimensions** (`ffprobe`). A tape that failed early still produces a valid, short, useless file. 4. **Check both halves survived concatenation** — sample a frame from each side. 5. **Confirm the "before" side actually fails.** If the bug did not fire, you have recorded two working takes and captioned one of them "before". ## Before/after in one file Record two takes, concat with ffmpeg: ```bash printf "file 'before.mp4'\nfile 'after.mp4'\n" > list.txt ffmpeg -y -f concat -safe 0 -i list.txt -c:v libx264 -preset slow -crf 28 \ -pix_fmt yuv420p -movflags +faststart demo.mp4 ``` `yuv420p` for player compatibility; `+faststart` so it streams. Terminal text at ~1300×700 encodes to a few hundred KB for 40s — small enough to inline as a data URI in an artifact. ## Finish - Kill anything the demo spawned. Identify processes by pidfile or `/proc//cmdline` argv[0] — `pgrep -f ` matches the checking shell's own arguments and reports phantoms. - Keep the video out of the repo. Publish it in an artifact and link that. - If the video only shows part of the story (memory growth is not watchable), say so and keep the rest as measurements. Do not stage what you cannot film.