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Timeline Control

Control exactly when your video layers appear and disappear in your composition. The timing system has two levels:

📹 Source Timing

Which part of the source video to use (trimming)

🎬 Composition Timing

When to show the layer in the final video

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Composition Timeline

Control when layers appear in your final video:

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Start Time

Set when a layer begins appearing: 
// Layer appears at 2 seconds
comp.add(transparent).start(2.0)

// Layer appears immediately (default)
comp.add(transparent).start(0.0)

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Duration Control

Control how long layers are visible: 
// Show for exactly 5 seconds
comp.add(transparent).start(2.0).duration(5.0)
// Appears at 2s, disappears at 7s

// Show from 10s to 15s
comp.add(transparent).start(10.0).end(15.0)
// Appears at 10s, disappears at 15s

// Show from start time until end of composition
comp.add(transparent).start(5.0)
// Appears at 5s, continues until composition ends

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Source Trimming

Use only specific parts of your source videos: 
// Use seconds 5-10 of the source video
const trimmed = transparent.subclip(5, 10)
comp.add(trimmed)

// Use from 3 seconds to end of source
const fromMiddle = transparent.subclip(3)
comp.add(fromMiddle)

// Or trim directly in composition
comp.add(transparent).subclip(2, 8)

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Combined Timing

You can combine source trimming with composition timing: 
// Use seconds 1-4 of source (3 seconds of content)
// Show it at 10-13 seconds in the final video
comp.add(transparent)
  .subclip(1, 4)      // Source: use 1-4s (3s of content)
  .start(10)          // Composition: show at 10s
  .duration(3)        // Composition: show for 3s (10-13s)

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Staggered Animations

Create dynamic sequences with layers appearing at different times: 
const videos = [transparent1, transparent2, transparent3, transparent4]
const positions = [
  Anchor.TOP_LEFT, Anchor.TOP_RIGHT,
  Anchor.BOTTOM_LEFT, Anchor.BOTTOM_RIGHT
]

videos.forEach((vid, i) => {
  comp.add(vid)
    .at(positions[i], 50, 50)
    .size(SizeMode.CANVAS_PERCENT, { percent: 40 })
    .start(i * 2)        // Start every 2 seconds: 0s, 2s, 4s, 6s
    .duration(6)         // Each visible for 6 seconds
    .opacity(0.8)
})

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Audio Timing

Control audio from your layers: 
// Layer with full audio
comp.add(transparent1)
  .start(0)
  .audio(true, 1.0)  // Full volume

// Layer with reduced audio
comp.add(transparent2)
  .start(5)
  .audio(true, 0.3)  // 30% volume

// Silent layer
comp.add(transparent3)
  .start(10)
  .audio(false)      // No audio

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Duration Rules

Understanding how composition duration is determined:

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Rule 1: Video Background Controls Duration

When you use a video background, it determines the final length: 
// 30-second background video = 30-second final composition
const bg = Background.fromVideo('30_second_bg.mp4')
const comp = new Composition(bg)
comp.add(transparent) // Even if foreground is 5 seconds

// Final video will be 30 seconds

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Rule 2: Color/Image Backgrounds Use Longest Foreground

Color and image backgrounds adapt to your content: 
// Color background adapts to content
const bg = Background.fromColor('#FF0000', 1920, 1080, 30)
const comp = new Composition(bg)
comp.add(tenSecondTransparent)    // 10-second transparent video
comp.add(fiveSecondTransparent)   // 5-second transparent video

// Final video will be 10 seconds (longest foreground)

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Rule 3: Explicit Duration Override

You can always force a specific duration: 
const comp = new Composition(anyBackground)
comp.setDuration(20.0) // Force 20-second duration
comp.add(transparent)

// Final video will be exactly 20 seconds

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Source Trimming

Use only specific parts of your source videos:

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Basic Trimming

// Method 1: Trim the foreground before adding
const trimmed = video.subclip(10, 20)  // Use seconds 10-20
comp.add(trimmed, 'segment')

// Method 2: Trim in the composition
comp.add(transparent).subclip(10, 20)

// Method 3: Open-ended trim (from 5s to end)
comp.add(transparent).subclip(5)

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Advanced Trimming

// Multiple segments from same source
comp.add(transparent).subclip(0, 3).start(0)      // 0-3s of source at 0s
comp.add(transparent).subclip(10, 15).start(5)   // 10-15s of source at 5s
comp.add(transparent).subclip(25, 30).start(12)   // 25-30s of source at 12s

// Re-trimming (trim a trimmed video)
const firstTrim = transparent.subclip(5, 20)    // 5-20s of original
const secondTrim = firstTrim.subclip(2, 8) // 2-8s of first trim = 7-13s of original

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Audio Synchronization

Control audio timing with your video layers:

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Audio with Timing

// Transparent video with audio that starts at 3 seconds
comp.add(transparent)
  .start(3.0)
  .audio(true, 1.0)  // Audio automatically delayed to match video

// Multiple audio sources with different timing
comp.add(transparent1).start(0).audio(true, 0.8)   // Main audio
comp.add(transparent2).start(5).audio(true, 0.3)      // Background music
comp.add(transparent3).start(10).audio(true, 0.5)   // Sound effects

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Audio Mixing

The system automatically mixes audio from multiple layers:
  • Single audio source: Used directly
  • Multiple audio sources: Mixed with volume control
  • Timing: Audio delays automatically match video timing

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Performance Tips

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Optimize for Speed

  • Shorter segments: Trim videos to only needed parts
  • Reasonable overlaps: Avoid too many overlapping layers
  • Fast encoding: Use faster encoder presets for testing

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Memory Management

  • Large videos: Consider trimming before composition
  • Many layers: Test with fewer layers first
  • Long compositions: Break into segments if needed

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What’s Next?

🎬 Export Your Video

Choose the right export format and quality settings

🍳 See Examples

Explore complete timing and animation examples