generate-background-music

name	generate-background-music
description	Generate ambient background music for social media videos using ElevenLabs Sound Effects API. Use when the user asks to "add background music", "generate music", "create bg music", "add ambient sound", "make background track", or wants music underneath their video voiceover.
version	0.1.0

Generate Background Music

Generate ambient background music for social media videos using the ElevenLabs Sound Effects API. The generated music is mixed at low volume underneath the voiceover track.

Requirements

• ElevenLabs API key (stored in .env file as ELEVENLABS_API_KEY)
• Node.js 18+ (for native fetch)
• ffmpeg (for mixing audio tracks)

API Configuration

• Endpoint: https://api.elevenlabs.io/v1/sound-generation
• Method: POST
• Output Format: MP3

API Call Pattern

import { readFileSync, writeFileSync } from "fs";

const API_KEY = "your-elevenlabs-api-key";

const response = await fetch(
  "https://api.elevenlabs.io/v1/sound-generation",
  {
    method: "POST",
    headers: {
      "xi-api-key": API_KEY,
      "Content-Type": "application/json",
      Accept: "audio/mpeg",
    },
    body: JSON.stringify({
      text: musicPrompt,          // Descriptive prompt for the music
      duration_seconds: duration,  // Duration in seconds (match video length)
      prompt_influence: 0.3,       // 0.0-1.0 — how closely to follow the prompt
    }),
  }
);

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

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

Music Prompt Guidelines

Write prompts that describe the mood and style of background music. Keep it concise and descriptive.

Recommended Prompts by Content Type

The music should be upbeat and energetic — keep viewers engaged, not sleepy. Since we mix at very low volume (1.5%), the track itself can be punchy and lively.

Content Type	Prompt
Business/Startup	upbeat modern background music, driving beat, synth bass, confident energy, startup vibe
Motivational	upbeat motivational background music, energetic drums, inspiring synths, fast tempo
Educational	upbeat electronic background music, light beat, modern, engaging rhythm
Hormozi/Offer	energetic confident background music, punchy beat, modern trap-inspired, business energy
Tech/SaaS	upbeat tech background music, electronic beats, futuristic synths, driving rhythm
Success Story	triumphant upbeat music, building energy, powerful drums, inspiring crescendo

Prompt Tips

• Always include "background music" in the prompt
• Use words like "upbeat", "energetic", "driving beat", "modern", "punchy" — we want energy, not a lullaby
• The track plays at 1.5% volume so it can be as lively as needed without overpowering voiceover
• Avoid words like "calm", "ambient", "relaxing", "soft" — these put viewers to sleep
• Match the energy to the video content — business content should feel confident and fast-paced

Mixing Audio with ffmpeg

After generating background music, mix it with the voiceover at reduced volume:

Mix voiceover + background music into one audio file

ffmpeg -y \
  -i voiceover.mp3 \
  -i bg_music.mp3 \
  -filter_complex "[0:a]volume=1.0[vo];[1:a]volume=0.015[bg];[vo][bg]amix=inputs=2:duration=first:dropout_transition=3:normalize=0[out]" \
  -map "[out]" -c:a aac -b:a 192k \
  mixed_audio.m4a

Key parameters:

• volume=1.0 on voiceover — voiceover MUST stay at 100% volume, this is non-negotiable
• volume=0.015 — background music at 1.5% volume — subtle texture underneath voiceover
• normalize=0 — CRITICAL: disables amix auto-normalization which otherwise halves the voiceover volume
• amix=inputs=2:duration=first — output length matches voiceover duration
• dropout_transition=3 — smooth fade out at the end

CRITICAL: Background Music Volume Rule

The voiceover MUST be the dominant audio. Background music must be barely perceptible — the viewer should feel it subconsciously, not hear it consciously. If you can clearly hear the music over the voice, it's TOO LOUD.

• Voiceover MUST be at volume=1.0 (100%) — never reduce voiceover volume
• Background music: use volume=0.015 (1.5%) as the standard — never higher than volume=0.03
• ALWAYS use normalize=0 in amix — without this, ffmpeg auto-normalizes and halves the voiceover
• After mixing, listen/check the waveform: the voiceover peaks should be 10-15x louder than bg music peaks
• When in doubt, go QUIETER on bg music

Merge mixed audio with video

ffmpeg -y \
  -i video.mp4 \
  -i mixed_audio.m4a \
  -c:v copy -c:a aac -b:a 192k -shortest \
  -map 0:v:0 -map 1:a:0 \
  final_video.mp4

Full Pipeline: Video + Voiceover + Background Music

1. Generate voiceover (see generate-voiceover skill)
2. Generate background music matching video duration with appropriate mood prompt
3. Mix audio tracks: voiceover at full volume + bg music at 1.5% volume
4. Merge with video: combine mixed audio with the rendered video

# Step 1: Mix voiceover + bg music (voiceover at 100%, bg at 1.5%, normalize OFF)
ffmpeg -y \
  -i voiceover.mp3 -i bg_music.mp3 \
  -filter_complex "[0:a]volume=1.0[vo];[1:a]volume=0.015[bg];[vo][bg]amix=inputs=2:duration=first:dropout_transition=3:normalize=0[out]" \
  -map "[out]" -c:a aac -b:a 192k mixed_audio.m4a

# Step 2: Merge with video
ffmpeg -y \
  -i video-9x16.mp4 -i mixed_audio.m4a \
  -c:v copy -c:a aac -b:a 192k -shortest \
  -map 0:v:0 -map 1:a:0 \
  final-video-9x16.mp4

Browser-Based API Call (Sandbox Workaround)

If the sandbox blocks direct API calls, use the Chrome browser JavaScript execution:

(async () => {
  const response = await fetch("https://api.elevenlabs.io/v1/sound-generation", {
    method: "POST",
    headers: {
      "xi-api-key": API_KEY,
      "Content-Type": "application/json",
      Accept: "audio/mpeg",
    },
    body: JSON.stringify({
      text: "upbeat modern background music, driving beat, synth bass, confident energy, startup vibe",
      duration_seconds: 25,
      prompt_influence: 0.3,
    }),
  });

  const blob = await response.blob();
  const url = URL.createObjectURL(blob);
  const a = document.createElement('a');
  a.href = url;
  a.download = 'bg_music.mp3';
  document.body.appendChild(a);
  a.click();
  a.remove();
  return `Success! Size: ${(blob.size / 1024).toFixed(1)} KB`;
})()

Then copy the downloaded file to the outputs folder and proceed with mixing.

Workflow

1. Determine the video duration and content mood
2. Write a music prompt matching the content tone
3. Call the ElevenLabs Sound Effects API
4. Save the MP3 output
5. Mix with ffmpeg: voiceover at volume=1.0, bg at volume=0.015, always normalize=0
6. Merge mixed audio with the video