Quick Start#

MediaComposer is used in Scripting to compose video, image, and audio timelines and export a final media file. It provides a stable and precise timeline model that supports video clips, image clips, audio overlays, fades, audio ducking, and flexible export configuration.

This module is suitable for:

• Mixing videos and images into a single output
• Adding background music, voice-over, or sound effects
• Generating videos from image sequences
• Automated and script-driven media production

#Design Overview

MediaComposer consists of three core layers:

1. Time Model Based on MediaTime and TimeRange for precise time representation

2. Timeline Model

   • VideoItem[]: visual timeline (videos or images, sequential)
   • AudioClip[]: audio timeline (positioned or sequential)

3. Export System A unified composeAndExport API for rendering and exporting

#Timeline Structure

timeline: {
  videoItems: VideoItem[]
  audioClips: AudioClip[]
}

• videoItems Defines the visual timeline. Video and image items are concatenated strictly in array order.
• audioClips Defines the audio timeline. Clips may be explicitly positioned or appended sequentially.

The final exported duration is determined by the videoItems timeline.

#VideoItem

type VideoItem = XOR<VideoClip, ImageClip>

A VideoItem represents a single visual segment in the timeline. It can be either a video clip or an image clip, but never both.

#VideoClip

type VideoClip = {
  videoPath: string
  sourceTimeRange?: TimeRange | null
  keepOriginalAudio?: boolean
  fade?: FadeConfig | null
}

#videoPath

• Path to the video file
• Local video files are supported

#sourceTimeRange

sourceTimeRange?: TimeRange | null

• Specifies the portion of the source video to use
• Defaults to the entire video when omitted

Common use cases:

• Trimming a video
• Extracting a specific segment as material

#keepOriginalAudio

keepOriginalAudio?: boolean

• Whether to keep the original audio from the video
• Default: false

Notes:

• When true, the video’s original audio participates in the final mix
• External audioClips may still be used simultaneously
• Ducking behavior is controlled by ExportOptions.ducking

#fade

fade?: FadeConfig | null

• Per-clip fade-in / fade-out configuration
• Overrides the global video fade when provided

#ImageClip

type ImageClip = {
  imagePath: string
  duration: MediaTime
  contentMode?: "fit" | "crop"
  backgroundColor?: Color
  fade?: FadeConfig | null
}

ImageClip allows a still image to appear as a timed segment within the video timeline.

#imagePath

• Path to the image file
• Common image formats are supported (JPEG, PNG, HEIC, etc.)

#duration

duration: MediaTime

• The display duration of the image clip in the video
• This field is required

#contentMode

contentMode?: "fit" | "crop"

• Controls how the image is scaled to the render size
• Default: fit

Behavior:

• fit: Entire image is visible; letterboxing may occur
• crop: Image fills the frame; excess is cropped

#backgroundColor

backgroundColor?: Color

• Background color for areas not covered by the image
• Commonly used together with fit mode

#fade

fade?: FadeConfig | null

• Fade-in / fade-out configuration for the image clip
• Behaves the same as fades for video clips

#AudioClip

type AudioClip = {
  path: string
  sourceTimeRange?: TimeRange | null
  at?: MediaTime
  volume?: number
  fade?: FadeConfig | null
  loopToFitVideoDuration?: boolean
}

AudioClip is used to add background music, narration, or sound effects to the final video.

#path

• Path to the audio file

#sourceTimeRange

• Specifies the portion of the audio to use
• Defaults to the entire audio file

#at

at?: MediaTime

• Explicit placement time on the final timeline
• When omitted, audio clips are appended sequentially

#volume

volume?: number

• Per-clip gain (0…1)
• Default: 1

#fade

• Fade-in / fade-out configuration for the audio clip

#loopToFitVideoDuration

loopToFitVideoDuration?: boolean

• Whether the audio should loop to match the total video duration
• Commonly used for background music

#FadeConfig

type FadeConfig = {
  fadeInSeconds?: number
  fadeOutSeconds?: number
}

• Duration is expressed in seconds
• Applicable to video, image, and audio clips
• Defaults to 0 when omitted

#ExportOptions

type ExportOptions = {
  renderSize?: Size
  frameRate?: number
  scaleMode?: VideoScaleMode
  globalVideoFade?: FadeConfig | null
  externalAudioBaseVolume?: number
  ducking?: DuckingConfig
  presetName?: ExportPreset
  outputFileType?: ExportFileType
}

#Common options

• renderSize Output resolution, default is 1080×1920

• frameRate Rendering frame rate, default is 30

• globalVideoFade Global fade applied to all visual clips unless overridden

• ducking Automatically lowers external audio volume when original video audio exists

• presetName / outputFileType Control encoding quality and output format

#composeAndExport

function composeAndExport(options: {
  exportPath: string
  timeline: {
    videoItems: VideoItem[]
    audioClips: AudioClip[]
  }
  exportOptions?: ExportOptions
  overwrite?: boolean
}): Promise<{
  exportPath: string
  duration: MediaTime
}>

#Parameters

• exportPath Output file path

• timeline.videoItems Visual timeline (videos and images, in sequence)

• timeline.audioClips Audio timeline (positioned or sequential)

• exportOptions Optional export configuration

• overwrite Whether to overwrite an existing file (default: true)

#Return Value

{
  exportPath: string
  duration: MediaTime
}

• exportPath: final output path
• duration: total duration of the exported video (derived from videoItems)

#Usage Guidelines and Best Practices

• Always use MediaTime for time values; avoid raw floating-point seconds
• ImageClip.duration must always be explicitly specified
• Audio and visual timelines are independent but mixed in the final output
• For complex projects, use a consistent timescale (e.g. 600)
• Background music typically uses loopToFitVideoDuration

#Typical Use Cases

• Mixed image and video composition
• Adding background music or narration to videos
• Automated video generation
• Script-driven content creation pipelines