> ## Documentation Index > Fetch the complete documentation index at: https://hyperframes.heygen.com/llms.txt > Use this file to discover all available pages before exploring further. # Media and audio > 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 companion 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 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 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 `