---
title: Media and audio
description: "Ask for the voiceover, music, sound, captions, cutouts, and assets a composition needs — with the precise, unambiguous phrasing the media pipeline acts on."
---

By now your video moves and reads right; this level gives it a voice. HyperFrames owns media *playback*; a sibling media pipeline resolves everything else — voice, music, sound effects, images, icons, logos, captions, and background removal. You reach all of it by describing what the composition needs, and the agent resolves each need to a frozen local file. The craft here is precision: vague media asks ("add some music," "no sound") are the ones that come back wrong, because the pipeline does exactly what the words say.

## Voiceover (TTS)

Text-to-speech runs locally through Kokoro — no API key needed — with a HeyGen TTS upsell behind it. Describe the content and the agent picks a fitting voice, or name the voice, tone, and speed directly:

> Generate narration for this script with a professional female voice.

> Add TTS voiceover, British male voice, at 1.1× speed.

The [Vocabulary](/prompting/vocabulary#text-to-speech-voices) table maps content types to Kokoro voices (for example `af_heart` / `af_nova` for a product demo, `am_adam` / `bf_emma` for a tutorial, `af_sky` / `am_michael` for marketing). Name one directly if you already know it; otherwise describe the read and let the agent choose.

- ❌ `add a voice`
- ✅ `warm, unhurried female narration of the quoted script` — tone and pace are what actually change the delivery

## Background music

Music resolves from a large catalog by mood, and it should almost always sit *under* the narration, not compete with it. Give the mood **and** a loudness target — the pipeline can duck and normalize to a level, so an explicit target lands a mix instead of a guess:

> Add subtle electronic BGM, kept under −18 dB so it stays beneath the voiceover.

> Upbeat tech-launch music bed at a low level, ducking under narration.

- ❌ `add background music` — you'll get a full-volume track fighting the VO
- ✅ `subtle background music, ducked ~12 dB under the voice` — a mix instruction the pipeline can execute

<Tip>
  A stated loudness target ("under −18 dB," "ducked under the voice") is the difference between music that supports the piece and music that buries it. When there's narration, always say the bed goes under it.
</Tip>

## Sound effects

SFX resolve from a small bundled library plus the catalog. Cue them to specific moments — a transition, a stamp-in, an impact — rather than sprinkling them:

> Add a whoosh on each of the three scene transitions.

> Put a soft click on the button press at 0:04.

## Pace reveals to the narration

Once a video has a voice, the voice is the clock — the next instruction that matters is telling the agent that on-screen elements land **on their spoken cues** — the stat appears as the narrator says it, not at some independent time the builder eyeballed. Without this, narration and visuals drift into two parallel tracks that happen to share a file:

> VO-paced reveals: each scene's elements land on their spoken cues; secondary elements keep resolving while the narrator is mid-thought; the scene is complete just as the narration moves on.

The capstone film applies exactly this rule to every region — its Direction block reads:

> VO-paced reveals: each region's elements land on their spoken cues as the camera arrives; secondary elements keep resolving while the camera is present; the region is complete just as the camera accelerates away.

Two practical notes: the agent gets word timings for free (the narration is transcribed with per-word timestamps, the same machinery behind [captions](#captions-and-transcription)), so "on its spoken cue" is a real, executable instruction — and the inverse rule matters just as much: the narration never waits for the visuals. Pace the camera and reveals to the voice, not the voice to the animation.

## Captions and transcription

Captions come from word-level timestamps. When you generate a voiceover, the timing comes with it; for existing footage, transcription produces the timing (Parakeet by default, with a whisper.cpp fallback). Scaffolding a project from a source video can generate captions from its audio directly.

> Transcribe the narration and add karaoke-style captions synced to it.

> Generate captions from `assets/interview.mp4` and style them hype, scale-pop.

Caption *look* is its own vocabulary (tone, size, per-word emphasis) — see [Captions catalog](/prompting/captions-catalog) for the styles. This page is about producing the timed text; that page is about styling it.

## Background removal (transparent cutouts)

The `remove-background` command mattes a subject out of a video or image locally and hands you a transparent WebM you can drop into any scene as a `<video>`:

> Remove the background from `assets/presenter.mp4` and float the subject over the scene.

One caveat is load-bearing: the built-in model is **purpose-built for people** — head-and-shoulders or full-body, reasonably stable framing, a background that contrasts with the subject. It returns a mostly-empty mask on **non-human subjects** (products, animals, objects). If you need to cut out a product, say so — the agent should route to a different tool rather than run the person model and get nothing.

- ❌ `remove the background from this product shot` with the built-in command — the human-matting model can't see it
- ✅ `matte the presenter out of assets/talk.mp4` (person) — or, for a product, flag that it's a non-human subject so a different matter is used

The [Remove background guide](/guides/remove-background) covers the person-only caveat, the two-layer plate for text-behind-subject, and alternatives for objects and hair-fine mattes.

## Video-in-video and picture-in-picture

Layering footage — a talking head over a scene, a subject in front of a headline, PiP inset — is a compositing prompt. Two grounded rules keep it frame-accurate, and the agent applies them for you, but naming the layout you want helps:

> Put the transparent presenter cutout in the bottom-right, over the chart scene.

> Layer the headline *behind* the presenter so their silhouette occludes the text.

<Note>
  Two mechanics the workflow skills handle automatically (from the [Remove background guide](/guides/remove-background#compositing-patterns-and-pitfalls)): a cutout that reveals into view is wrapped in a non-timed `<div>` and the *wrapper* is animated (the framework forces `opacity: 1` on timed clips, so animating the video directly does nothing); and both the base video and the cutout mount at `data-start="0"` so their decoders stay in sync at the cut. You rarely need to say this — but it's why "late-mounting" a PiP clip can land a frame off.
</Note>

## Bring any footage

You don't need to pre-convert supplied footage before naming it in a prompt. If a clip's codec doesn't play back cleanly in a browser — HEVC (H.265) is the common case, straight off an iPhone or a screen recorder — the framework probes the asset and builds a bounded H.264 proxy automatically, cached under `.transcode-cache/`. `preview`, `play`, Studio, and published player pages use the proxy for playback; a render always decodes the original file, so nothing about final quality or color is touched. `hyperframes lint` also flags the asset at info level (`hevc_preview_codec`) so you know a proxy is in play, and it's optional — `--no-proxy` per command, or `media.autoProxy: false` in `hyperframes.json` project-wide. The same mechanism covers alpha-channel sources too (ProRes 4444, alpha WebM proxy to VP9+Opus WebM instead of being refused), so a transparent cutout in a hostile codec isn't a blocker either.

None of this changes how you phrase the ask: name the footage by path like any other supplied asset, and describe the composition you want built from it.

> Build a short picture-in-picture piece from `source-hevc.mp4` — inset it bottom-right over a full-bleed background scene, with a soft rounded border.

<video controls muted loop playsinline preload="metadata" src="https://static.heygen.ai/hyperframes-oss/docs/images/prompting/proxy-footage.mp4#t=0.1" style={{ borderRadius: "0.5rem", marginTop: "0.75rem" }}></video>
*Rendered from the prompt above, unedited — the source clip is a plain H.265/HEVC file; render decoded it directly via FFmpeg, while preview would have used the automatic H.264 proxy.*

See the [Rendering guide](/guides/rendering#input-video-codecs) for the mechanics — proxy generation, caching, and which codecs it covers.

## The supplied-assets rule

For any asset you already have, an explicit path is the instruction that removes the most ambiguity. The agent will search when you describe an asset, but a path removes every ambiguity about *which* file — and for your own brand assets, it's the only way to guarantee the right one:

- ❌ `use my logo`
- ✅ `use assets/logo.svg`

This matters even when resolution would otherwise work: brand and entity assets should point at *your* file, not a resolved lookalike. (Third-party logos are a separate case — the pipeline pulls official marks from a logo cascade and never hand-redraws them, so "add the LinkedIn logo" is fine; "add my company's logo" needs a path.)

## Say what "no sound" actually means

The most common audio mistake is a negative that means less than you think. "No narration" removes the voiceover — it does **not** silence music or sound effects. If you want genuine silence, say so:

- ❌ `no narration` when you mean a completely silent video — music and SFX can still be added
- ✅ `no audio at all` — the unambiguous way to ask for silence

This mirrors the negatives discipline in [Anatomy](/prompting/anatomy): close the gap explicitly, because the engine acts on the literal words.

## Related

<CardGroup cols={2}>
  <Card title="Vocabulary" href="/prompting/vocabulary">Voice names, caption tones, and audio-reactive mappings</Card>
  <Card title="Captions catalog" href="/prompting/captions-catalog">Styling the timed text this page produces</Card>
  <Card title="Remove background guide" href="/guides/remove-background">The matting command, its person-only caveat, and alternatives</Card>
  <Card title="Video components" href="/guides/video-components">Installable overlays, captions, and effects</Card>
</CardGroup>

<Note>
**Capstone thread** — the [Level 7 film](/prompting/capstone)'s Material region runs this chapter's entire pipeline on one clip: generated footage → HEVC auto-proxy → background removal mid-scene → word-synced captions from the clip's own transcription, with the clip's audio ducking the BGM (cut from the film, below).
</Note>

This is the clause in the [full capstone prompt](/prompting/capstone#the-full-prompt-verbatim) that buys the piece — prompt language you can lift for your own video:

> […] a real talking-head clip (generate a short clip of a person speaking one neutral line via the media pipeline's avatar video generation […] **transcode it to HEVC `hvc1`** so the automatic proxy subsystem carries preview) sits as a clip on the wire. The order of operations IS the story: as the camera arrives and BEFORE the person speaks, the framework mattes the footage — **the background peels away via background removal** […] THEN they speak, and the main **keywords of their own line — derived from the clip's transcription — land word-synced** […] The clip's own audio ducks the BGM briefly; the VO resumes as the camera pulls away.

<video controls muted loop playsinline preload="metadata" src="https://static.heygen.ai/hyperframes-oss/docs/images/prompting/capstone-region-material.mp4#t=0.1" style={{ borderRadius: "0.5rem", marginTop: "0.75rem" }}></video>
*That clause, rendered — the region cut from the finished film.*

*Next: [Design systems and brand](/prompting/design-systems) — pointing the agent at a source of brand truth instead of describing a vibe.*
