Skip to main content
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 describe what the composition needs. The agent resolves each need to a frozen local file. Precision is the whole craft here. Vague asks come back wrong. “Add some music” and “no sound” are the two that bite most often, because the pipeline does exactly what the words say.

​
Voiceover (TTS)

The agent picks a voice engine in a fixed order. HeyGen Starfish goes first if your HeyGen account is configured. ElevenLabs is next if that key is set. Otherwise the local Kokoro model runs, and it needs no API key. Describe the content and let the agent pick a fitting voice. Or name the voice, tone, and speed yourself:
Generate narration for this script with a professional female voice.
Add TTS voiceover, British male voice, at 1.1× speed.
The Vocabulary table maps content types to Kokoro voices. af_heart and af_nova suit a product demo. am_adam and bf_emma suit a tutorial. af_sky and am_michael suit marketing. Name a voice 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. It should almost always sit under the narration rather than 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
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.

​
Sound effects

SFX resolve from a bundled 19-file library plus the catalog. Cue them to specific moments — a transition, a stamp-in, an impact. Don’t sprinkle 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. Say 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. Skip this and 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. Narration is transcribed with per-word timestamps — the same machinery behind captions. So “on its spoken cue” is a real, executable instruction. The inverse rule matters just as much. The narration never waits for the visuals. Pace the camera and the reveals to the voice, not the voice to the animation.

​
Captions and transcription

Captions come from word-level timestamps. Generate a voiceover and the timing comes with it. For existing footage, transcription produces the timing: Parakeet runs when it’s installed, and whisper handles it otherwise. 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 the 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. You get back 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 (u2net_human_seg) is purpose-built for people: head-and-shoulders or full-body, reasonably stable framing, a background that contrasts with the subject. On non-human subjects — products, animals, objects — it returns a mostly-empty mask. So if you need to cut out a product, say so. The agent should route to a different tool instead of running the person model and getting 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 for a person. For a product, flag that it’s a non-human subject so a different matter is used.
The Remove background guide 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 is a compositing prompt: a talking head over a scene, a subject in front of a headline, a PiP inset. The agent applies the frame-accuracy rules for you. Naming the layout you want still 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.
Two mechanics the workflow skills handle automatically, from the Remove background guide:
  • A cutout that reveals into view goes inside a non-timed <div>, and the wrapper is what gets animated. HyperFrames owns clip visibility, so animating the media element directly fights the clip lifecycle.
  • The base video and the cutout both mount at data-start="0", so their decoders stay in sync at the cut.
You rarely need to say either one. They’re why “late-mounting” a PiP clip can land a frame off.

​
Bring any footage

You don’t need to pre-convert supplied footage before naming it in a prompt. Some codecs don’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 that 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. Proxying is optional. Pass --no-proxy per command, or set media.autoProxy: false in hyperframes.json project-wide. The same mechanism covers alpha-channel sources. ProRes 4444 and alpha WebM get a VP8 + Opus WebM proxy 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.
Rendered from the prompt above, unedited. The source clip is a plain H.265/HEVC file. The render decoded it directly via FFmpeg. Preview would have used the automatic H.264 proxy. See the Rendering guide for the mechanics — proxy generation, caching, and which codecs it covers.

​
The supplied-assets rule

For any asset you already have, an explicit path removes the most ambiguity. The agent will search when you only describe an asset. A path settles which file.
  • ❌ use my logo
  • ✅ use assets/logo.svg
This matters even when a search would have worked. 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 redraws them by hand. 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. Close the gap explicitly, because the engine acts on the literal words.

​
The capstone thread

Capstone thread — the Level 7 film’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).
This is the clause in the full capstone prompt that buys the piece. It’s 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.
That clause, rendered — the region cut from the finished film. Next: Design systems and brand — pointing the agent at a source of brand truth instead of describing a vibe.