Input tracks

Access media track information and read packets from input files

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.

InputTrack

Base class representing a media track in an input file.

Properties

input · Input

The input file this track belongs to.

type · TrackType

The type of the track (‘video’, ‘audio’, or ‘subtitle’).

codec · MediaCodec | null

The codec of the track’s packets.

id · number

The unique ID of this track in the input file.

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.

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.

languageCode · string

The ISO 639-2/T language code for this track. If the language is unknown, this field is 'und' (undetermined).

name · string | null

A user-defined name for this track.

timeResolution · number

A positive number x such that all timestamps and durations of all packets of this track are integer multiples of 1/x.

disposition · TrackDisposition

The track’s disposition, i.e. information about its intended usage.

Methods

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.

computeDuration()

async computeDuration(): Promise<number>

Returns the end timestamp of the last packet of this track, in seconds.

getCodecParameterString()

async getCodecParameterString(): Promise<string | null>

Returns the full codec parameter string for this track.

canDecode()

async canDecode(): Promise<boolean>

Checks if this track’s packets can be decoded by the browser.

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.

computePacketStats()

async computePacketStats(targetPacketCount?: number): Promise<PacketStats>

Computes aggregate packet statistics for this track, such as average packet rate or bitrate.

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.

return · PacketStats

Show PacketStats properties

packetCount · number

The total number of packets.

averagePacketRate · number

The average number of packets per second. For video tracks, this will equal the average frame rate (FPS).

averageBitrate · number

The average number of bits per second.

isVideoTrack()

isVideoTrack(): this is InputVideoTrack

Returns true if and only if this track is a video track.

isAudioTrack()

isAudioTrack(): this is InputAudioTrack

Returns true if and only if this track is an audio track.

InputVideoTrack

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

Properties

codec · VideoCodec | null

The video codec of this track.

codedWidth · number

The width in pixels of the track’s coded samples, before any transformations or rotations.

codedHeight · number

The height in pixels of the track’s coded samples, before any transformations or rotations.

rotation · Rotation

The angle in degrees by which the track’s frames should be rotated (clockwise). Can be 0, 90, 180, or 270.

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).

squarePixelWidth · number

The width of the track’s frames in square pixels, adjusted for pixel aspect ratio but before rotation.

squarePixelHeight · number

The height of the track’s frames in square pixels, adjusted for pixel aspect ratio but before rotation.

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.

Methods

getColorSpace()

async getColorSpace(): Promise<VideoColorSpaceInit>

Returns the color space of the track’s samples.

hasHighDynamicRange()

async hasHighDynamicRange(): Promise<boolean>

If this method returns true, the track’s samples use a high dynamic range (HDR).

canBeTransparent()

async canBeTransparent(): Promise<boolean>

Checks if this track may contain transparent samples with alpha data.

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.

InputAudioTrack

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

Properties

codec · AudioCodec | null

The audio codec of this track.

numberOfChannels · number

The number of audio channels in the track.

sampleRate · number

The track’s audio sample rate in hertz.

Methods

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.

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`);
}