video-audio-design

Key principles

1. Layered audio architecture - Every video has three audio layers: narration on top (loudest), SFX in the middle (accent volume), and background music at the base (lowest).

2. Narration drives timing - Generate narration first, measure its duration, then set scene timing to match. Never fit narration into arbitrary scene lengths.

3. Duck music during speech - Background music must drop 50-60% when narration plays. Use smooth ramps (10-15 frames) to avoid jarring jumps.

4. SFX as accents, not distractions - Keep SFX short (under 0.5s), subtle in volume, and relevant to on-screen action.

5. Test audio in context - Always preview the full mix with all layers together. Listen for muddy speech, volume spikes, or dead silence.

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Core concepts

3-layer audio architecture

ElevenLabs API model

ElevenLabs provides neural TTS via a REST API. The core flow:

1. Pick a voice (pre-made or cloned) - each has a voice_id
2. Send text + voice settings to /v1/text-to-speech/{voice_id}
3. Receive raw audio bytes (mp3 by default)
4. Write to file and measure duration for scene timing

Voice settings:

Audio ducking concept

Audio ducking reduces background music volume when narration starts and restores it when narration ends. In Remotion, use interpolate():

Music volume:  0.4 ---\              /--- 0.4
                       \            /
               0.15     \__________/
                     narration start → end

Ramps should take 10-15 frames (~0.3-0.5s at 30fps).

Frame-based audio sync in Remotion

• useCurrentFrame() returns the current frame number
• interpolate() maps frame ranges to value ranges (e.g., volume)
• <Sequence from={frame}> places audio at a specific frame
• <Audio volume={fn}> accepts a static number or a per-frame function

Convert seconds to frames: frames = seconds * fps.

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Common tasks

1. Set up ElevenLabs API key and generate narration

import fs from 'fs';

const ELEVENLABS_API_URL = 'https://api.elevenlabs.io/v1';

async function generateNarration(
  text: string,
  voiceId: string,
  outputPath: string
): Promise<void> {
  const response = await fetch(
    `${ELEVENLABS_API_URL}/text-to-speech/${voiceId}`,
    {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        'xi-api-key': process.env.ELEVEN_LABS_API_KEY!,
      },
      body: JSON.stringify({
        text,
        model_id: 'eleven_multilingual_v2',
        voice_settings: {
          stability: 0.5,
          similarity_boost: 0.75,
          style: 0.5,
          use_speaker_boost: true,
        },
      }),
    }
  );

  if (!response.ok) {
    const error = await response.text();
    throw new Error(`ElevenLabs API error ${response.status}: ${error}`);
  }

  const buffer = Buffer.from(await response.arrayBuffer());
  fs.writeFileSync(outputPath, buffer);
}

2. Select and configure voice settings

Voice selection questions: gender, age range, accent, energy level, warmth.

interface VoiceSettings {
  stability: number;
  similarity_boost: number;
  style: number;
  use_speaker_boost: boolean;
}

const presets: Record<string, VoiceSettings> = {
  explainer: { stability: 0.6, similarity_boost: 0.75, style: 0.4, use_speaker_boost: true },
  promo: { stability: 0.3, similarity_boost: 0.7, style: 0.7, use_speaker_boost: true },
  tutorial: { stability: 0.7, similarity_boost: 0.8, style: 0.2, use_speaker_boost: false },
};

3. Generate narration per scene from a script

import { execSync } from 'child_process';
import path from 'path';

interface Scene { id: string; narrationText: string; }
interface SceneWithAudio extends Scene {
  audioPath: string;
  durationMs: number;
  durationFrames: number;
}

function getAudioDurationMs(filePath: string): number {
  const output = execSync(
    `ffprobe -v error -show_entries format=duration -of csv=p=0 "${filePath}"`
  ).toString().trim();
  return Math.round(parseFloat(output) * 1000);
}

async function generateSceneNarrations(
  scenes: Scene[], voiceId: string, outputDir: string, fps: number
): Promise<SceneWithAudio[]> {
  const results: SceneWithAudio[] = [];
  for (const scene of scenes) {
    const audioPath = path.join(outputDir, `${scene.id}.mp3`);
    await generateNarration(scene.narrationText, voiceId, audioPath);
    const durationMs = getAudioDurationMs(audioPath);
    results.push({
      ...scene, audioPath, durationMs,
      durationFrames: Math.ceil((durationMs / 1000) * fps),
    });
  }
  return results;
}

4. Source background music

Royalty-free music sources:

• Pixabay Audio: https://pixabay.com/music/ (free, no attribution)
• Freesound: https://freesound.org/ (CC0/CC-BY)
• YouTube Audio Library: download from YouTube Studio
• Local files: place in public/audio/ for Remotion's staticFile()

5. Generate SFX with FFmpeg

# Click sound - short sine burst
ffmpeg -f lavfi -i "sine=frequency=800:duration=0.05" \
  -af "afade=t=out:st=0.02:d=0.03" click.wav

# Keyboard typing - filtered noise burst
ffmpeg -f lavfi -i "anoisesrc=d=0.08:c=white:a=0.3" \
  -af "highpass=f=2000,lowpass=f=8000,afade=t=out:st=0.04:d=0.04" type.wav

# Whoosh - frequency sweep
ffmpeg -f lavfi -i "sine=frequency=200:duration=0.4" \
  -af "vibrato=f=8:d=0.5,afade=t=in:d=0.1,afade=t=out:st=0.2:d=0.2,lowpass=f=1000" \
  whoosh.wav

# Ding/chime - bell synthesis
ffmpeg -f lavfi -i "sine=frequency=1200:duration=0.6" \
  -af "afade=t=out:st=0.1:d=0.5,aecho=0.8:0.88:40:0.4" ding.wav

# Pop - impulse
ffmpeg -f lavfi -i "sine=frequency=400:duration=0.08" \
  -af "afade=t=out:st=0.02:d=0.06,lowpass=f=600" pop.wav

# Transition swoosh
ffmpeg -f lavfi -i "sine=frequency=300:duration=0.3" \
  -af "vibrato=f=12:d=0.8,afade=t=in:d=0.05,afade=t=out:st=0.15:d=0.15,bandpass=f=500:w=400" \
  swoosh.wav

6. Implement audio ducking in Remotion

import React from 'react';
import { Audio, useCurrentFrame, interpolate, Sequence } from 'remotion';

const AudioMixer: React.FC<{
  narrationSrc: string;
  musicSrc: string;
  narrationStart: number;
  narrationDuration: number;
}> = ({ narrationSrc, musicSrc, narrationStart, narrationDuration }) => {
  const frame = useCurrentFrame();

  const duckRampFrames = 10;
  const musicVolume = interpolate(
    frame,
    [
      narrationStart - duckRampFrames,
      narrationStart,
      narrationStart + narrationDuration,
      narrationStart + narrationDuration + duckRampFrames,
    ],
    [0.4, 0.15, 0.15, 0.4],
    { extrapolateLeft: 'clamp', extrapolateRight: 'clamp' }
  );

  return (
    <>
      <Audio src={musicSrc} volume={musicVolume} />
      <Sequence from={narrationStart} durationInFrames={narrationDuration}>
        <Audio src={narrationSrc} volume={0.9} />
      </Sequence>
    </>
  );
};

export default AudioMixer;

7. Mix 3 audio layers in a Remotion composition

import React from 'react';
import { Audio, Sequence, useCurrentFrame, interpolate } from 'remotion';

interface NarrationSegment { src: string; startFrame: number; durationFrames: number; }
interface SfxEvent { src: string; frame: number; }

const FullAudioMix: React.FC<{
  narrations: NarrationSegment[];
  sfxEvents: SfxEvent[];
  musicSrc: string;
}> = ({ narrations, sfxEvents, musicSrc }) => {
  const frame = useCurrentFrame();
  const duckRamp = 10;

  let musicVolume = 0.4;
  for (const seg of narrations) {
    const duck = interpolate(
      frame,
      [seg.startFrame - duckRamp, seg.startFrame,
       seg.startFrame + seg.durationFrames, seg.startFrame + seg.durationFrames + duckRamp],
      [1, 0.375, 0.375, 1],
      { extrapolateLeft: 'clamp', extrapolateRight: 'clamp' }
    );
    musicVolume = musicVolume * duck;
  }

  return (
    <>
      <Audio src={musicSrc} volume={musicVolume} loop />
      {sfxEvents.map((sfx, i) => (
        <Sequence key={i} from={sfx.frame} durationInFrames={30}>
          <Audio src={sfx.src} volume={0.4} />
        </Sequence>
      ))}
      {narrations.map((seg, i) => (
        <Sequence key={i} from={seg.startFrame} durationInFrames={seg.durationFrames}>
          <Audio src={seg.src} volume={0.9} />
        </Sequence>
      ))}
    </>
  );
};

export default FullAudioMix;

8. Use alternative TTS providers

OpenAI TTS - good quality, simple API, six built-in voices:

import OpenAI from 'openai';
import fs from 'fs';

const openai = new OpenAI();

async function generateWithOpenAI(
  text: string,
  outputPath: string,
  voice: 'alloy' | 'echo' | 'fable' | 'onyx' | 'nova' | 'shimmer' = 'alloy'
): Promise<void> {
  const mp3 = await openai.audio.speech.create({
    model: 'tts-1-hd',
    voice,
    input: text,
  });
  const buffer = Buffer.from(await mp3.arrayBuffer());
  fs.writeFileSync(outputPath, buffer);
}

Edge TTS - free, many voices, uses Microsoft Edge's TTS service:

pip install edge-tts
edge-tts --voice en-US-AriaNeural --text "Hello world" --write-media output.mp3
edge-tts --list-voices

---

Anti-patterns / common mistakes

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Gotchas

1. ElevenLabs rate limits and character quotas - The free tier has a monthly character limit. Cache generated audio aggressively and only regenerate when text changes. Use a hash of the text as the cache key.

2. MP3 encoder padding adds silence - MP3 files often have 20-50ms of silence at the start. Trim with ffmpeg -af silenceremove=1:0:-50dB or account for the offset in frame timing.

3. Remotion Audio volume is per-component, not global - Two <Audio> components at volume 1.0 can clip. Keep total volume across simultaneous layers under 1.0.

4. FFmpeg SFX sound different across systems - Always specify -ar 44100 -sample_fmt s16 for consistent output across machines.

5. Voice consistency across scenes - ElevenLabs can produce different tones for the same settings with varying text. Use stability >= 0.5 for multi-scene narration.

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References

For detailed patterns on specific audio sub-domains, read the relevant file from the references/ folder:

• references/elevenlabs-api.md - advanced ElevenLabs API patterns including voice cloning, streaming TTS, websocket API, pronunciation dictionaries, and quota management
• references/audio-mixing-patterns.md - advanced mixing patterns including multi-segment ducking, crossfades between scenes, volume automation curves, and mastering the final mix
• references/sfx-generation.md - comprehensive SFX generation with FFmpeg including complex synthesis, layering multiple generators, and building a reusable SFX library

Only load a references file if the current task requires it - they are long and will consume context.

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Companion check

On first activation of this skill in a conversation: check which companion skills are installed by running ls ~/.claude/skills/ ~/.agent/skills/ ~/.agents/skills/ .claude/skills/ .agent/skills/ .agents/skills/ 2>/dev/null. Compare the results against the recommended_skills field in this file's frontmatter. For any that are missing, mention them once and offer to install:

npx skills add AbsolutelySkilled/AbsolutelySkilled --skill <name>

Skip entirely if recommended_skills is empty or all companions are already installed.