> ## Documentation Index
> Fetch the complete documentation index at: https://docs.decktalk.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Product demos

> Narrate a feature over the screen it runs on, and rebuild the one section a product change touched.

A viewer sees the feature narrated over the screen it runs on, with every callout landing on the
word that names it.

A demo ages faster than anything else a company publishes, because the product moves every week. In
DeckTalk the demo is text and code, so a renamed button is a one-line edit and a rebuild of the
section that shows it. Nothing else is recorded again, and nothing else is voiced again.

## What a viewer gets

* Each callout, arrow and highlight appears on the word that names it, so the eye is never hunting
  for what the voice is talking about.
* Real product footage, because a section can be a screen recording rather than a page.
* A cut with no dead air, because DeckTalk cuts the video to the narration and not the other way
  round.
* Captions, chapters and a transcript page, which a demo needs on a site where most viewers watch
  with the sound off.

## What the author writes

| File            | What it holds                                                                              |
| --------------- | ------------------------------------------------------------------------------------------ |
| `script.md`     | The pitch, one heading per section, with a time budget that keeps the whole demo short.    |
| `decktalk.toml` | The sections, the voice and the `clip` value on any section that plays a screen recording. |
| `cues.json`     | The phrase each callout starts on.                                                         |
| The deck page   | The title cards, the callouts and the closing card.                                        |

A screen recording enters the video as a clip section. The section names its file in
`decktalk.toml`, and `decktalk clip` cuts a span of a built section and its narration into a clip
file and its words file. A sound effect lands on a cue through a `[[mix.sfx]]` entry, and the music
bed comes from the `[soundscape.music]` table.

## The workflow

<Steps>
  <Step title="Write the pitch first">
    Write `script.md` before the slides, because the words decide the cuts. Keep each section to its
    budget and read it aloud once.
  </Step>

  <Step title="Build it without voice">
    `decktalk build --no-voice` gives a complete video with placeholder narration, which is enough
    to judge the pacing before anyone spends a credit.
  </Step>

  <Step title="Drop the product footage in">
    Add a clip section for each screen recording, then run `decktalk verify` to see every seam
    between a page section and a clip section.
  </Step>

  <Step title="Voice it and check the landings">
    `decktalk preflight` freezes every reveal and estimates the run, then a voiced build writes the
    takes. `decktalk verify` reports every cue that did not land on its word.
  </Step>

  <Step title="Rebuild the section the product change touched">
    Edit the sentence or the callout, then run `decktalk build --only 3`. Every other section keeps
    its take and its recording.
  </Step>
</Steps>

Read [Quickstart](/quickstart) for the first build, [Add a clip section](/guides/clip-section) for
screen recordings, and [Put a sound effect on a cue](/guides/sfx-on-a-cue) for the accents a demo
lives on.

The other two use cases with worked examples are
[technical tutorials](/use-cases/technical-tutorials) and [lessons](/use-cases/lessons).