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Documentation Index

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Input tracks represent individual media streams (video, audio) within an input file. They provide access to track properties, codec information, and methods for reading encoded packets or decoded samples.

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InputTrack

Base class representing a media track in an input file.

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Properties

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input
Input
The input file this track belongs to.
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type
TrackType
The type of the track (‘video’, ‘audio’, or ‘subtitle’).
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codec
MediaCodec | null
The codec of the track’s packets.
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id
number
The unique ID of this track in the input file.
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number
number
The 1-based index of this track among all tracks of the same type in the input file. For example, the first video track has number 1, the second video track has number 2, and so on.
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internalCodecId
string | number | Uint8Array | null
The identifier of the codec used internally by the container. It is not homogenized by Mediabunny and depends entirely on the container format.
  • For ISOBMFF files, this field returns the name of the Sample Description Box (e.g. 'avc1').
  • For Matroska files, this field returns the value of the CodecID element.
  • For WAVE files, this field returns the value of the format tag in the 'fmt ' chunk.
  • For ADTS files, this field contains the MPEG-4 Audio Object Type.
  • For MPEG-TS files, this field contains the streamType value from the Program Map Table.
  • In all other cases, this field is null.
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languageCode
string
The ISO 639-2/T language code for this track. If the language is unknown, this field is 'und' (undetermined).
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name
string | null
A user-defined name for this track.
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timeResolution
number
A positive number x such that all timestamps and durations of all packets of this track are integer multiples of 1/x.
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disposition
TrackDisposition
The track’s disposition, i.e. information about its intended usage.

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Methods

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getFirstTimestamp()

async getFirstTimestamp(): Promise<number>
Returns the start timestamp of the first packet of this track, in seconds. While often near zero, this value may be positive or even negative. A negative starting timestamp means the track’s timing has been offset. Samples with a negative timestamp should not be presented.

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computeDuration()

async computeDuration(): Promise<number>
Returns the end timestamp of the last packet of this track, in seconds.

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getCodecParameterString()

async getCodecParameterString(): Promise<string | null>
Returns the full codec parameter string for this track.

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canDecode()

async canDecode(): Promise<boolean>
Checks if this track’s packets can be decoded by the browser.

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determinePacketType()

async determinePacketType(packet: EncodedPacket): Promise<PacketType | null>
For a given packet of this track, this method determines the actual type of this packet (key/delta) by looking into its bitstream. Returns null if the type couldn’t be determined.

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computePacketStats()

async computePacketStats(targetPacketCount?: number): Promise<PacketStats>
Computes aggregate packet statistics for this track, such as average packet rate or bitrate.
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targetPacketCount
number
Optional parameter that sets a target for how many packets this method must have looked at before it can return early. This means you can use it to aggregate only a subset (prefix) of all packets. This is very useful for getting a great estimate of video frame rate without having to scan through the entire file.
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return
PacketStats

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isVideoTrack()

isVideoTrack(): this is InputVideoTrack
Returns true if and only if this track is a video track.

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isAudioTrack()

isAudioTrack(): this is InputAudioTrack
Returns true if and only if this track is an audio track.

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InputVideoTrack

Represents a video track in an input file. Extends InputTrack with video-specific properties and methods.

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Properties

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codec
VideoCodec | null
The video codec of this track.
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codedWidth
number
The width in pixels of the track’s coded samples, before any transformations or rotations.
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codedHeight
number
The height in pixels of the track’s coded samples, before any transformations or rotations.
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rotation
Rotation
The angle in degrees by which the track’s frames should be rotated (clockwise). Can be 0, 90, 180, or 270.
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pixelAspectRatio
Rational
The pixel aspect ratio of the track’s frames, as a rational number in its reduced form. Most videos use square pixels (1:1).
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squarePixelWidth
number
The width of the track’s frames in square pixels, adjusted for pixel aspect ratio but before rotation.
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squarePixelHeight
number
The height of the track’s frames in square pixels, adjusted for pixel aspect ratio but before rotation.
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displayWidth
number
The display width of the track’s frames in pixels, after aspect ratio adjustment and rotation.
​
displayHeight
number
The display height of the track’s frames in pixels, after aspect ratio adjustment and rotation.

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Methods

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getColorSpace()

async getColorSpace(): Promise<VideoColorSpaceInit>
Returns the color space of the track’s samples.

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hasHighDynamicRange()

async hasHighDynamicRange(): Promise<boolean>
If this method returns true, the track’s samples use a high dynamic range (HDR).

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canBeTransparent()

async canBeTransparent(): Promise<boolean>
Checks if this track may contain transparent samples with alpha data.

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getDecoderConfig()

async getDecoderConfig(): Promise<VideoDecoderConfig | null>
Returns the decoder configuration for decoding the track’s packets using a VideoDecoder. Returns null if the track’s codec is unknown.

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InputAudioTrack

Represents an audio track in an input file. Extends InputTrack with audio-specific properties and methods.

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Properties

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codec
AudioCodec | null
The audio codec of this track.
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numberOfChannels
number
The number of audio channels in the track.
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sampleRate
number
The track’s audio sample rate in hertz.

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Methods

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getDecoderConfig()

async getDecoderConfig(): Promise<AudioDecoderConfig | null>
Returns the decoder configuration for decoding the track’s packets using an AudioDecoder. Returns null if the track’s codec is unknown.

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Example

import { Input, FileSource, Mp4InputFormat } from '@mediabunny/browser';

const input = new Input({
  formats: [Mp4InputFormat],
  source: new FileSource(file)
});

const videoTrack = await input.getPrimaryVideoTrack();
if (videoTrack) {
  console.log(`Codec: ${videoTrack.codec}`);
  console.log(`Resolution: ${videoTrack.codedWidth}x${videoTrack.codedHeight}`);
  console.log(`Display: ${videoTrack.displayWidth}x${videoTrack.displayHeight}`);
  console.log(`Rotation: ${videoTrack.rotation}°`);
  
  const stats = await videoTrack.computePacketStats(100);
  console.log(`Frame rate: ${stats.averagePacketRate.toFixed(2)} fps`);
  console.log(`Bitrate: ${(stats.averageBitrate / 1000000).toFixed(2)} Mbps`);
  
  const canDecode = await videoTrack.canDecode();
  console.log(`Can decode: ${canDecode}`);
}

const audioTrack = await input.getPrimaryAudioTrack();
if (audioTrack) {
  console.log(`Codec: ${audioTrack.codec}`);
  console.log(`Channels: ${audioTrack.numberOfChannels}`);
  console.log(`Sample rate: ${audioTrack.sampleRate} Hz`);
}

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