309 lines
11 KiB
Markdown
309 lines
11 KiB
Markdown
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---
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title: Glossary
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---
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## General - Media ##
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###### ABR
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Adaptive Bitrate. An ABR algorithm is an algorithm that selects between a number
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of [tracks](#track) during playback, where each track presents the same media
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but at different bitrates.
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###### Adaptive streaming
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In adaptive streaming, multiple [tracks](#track) are available that present the
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same media at different bitrates. The selected track is chosen dynamically
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during playback using an [ABR](#abr) algorithm.
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###### Access unit
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A data item within a media [container](#container). Generally refers to a small
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piece of the compressed media bitstream that can be decoded and presented to the
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user (a video picture or fragment of playable audio).
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###### AV1
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AOMedia Video 1 [codec](#codec).
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For more information, see the
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[Wikipedia page](https://en.wikipedia.org/wiki/AV1).
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###### AVC
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Advanced Video Coding, also known as the H.264 video [codec](#codec).
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For more information, see the
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[Wikipedia page](https://en.wikipedia.org/wiki/Advanced_Video_Coding).
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###### Codec
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This term is overloaded and has multiple meanings depending on the context. The
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two following definitions are the most commonly used:
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* Hardware or software component for encoding or decoding
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[access units](#access-unit).
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* Audio or video sample format specification.
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###### Container
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A media container format such as MP4 and Matroska. Such formats are called
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container formats because they contain one or more [tracks](#track) of media,
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where each track uses a particular [codec](#codec) (e.g. AAC audio and H.264
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video in an MP4 file). Note that some media formats are both a container format
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and a codec (e.g. MP3).
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###### DASH
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Dynamic [Adaptive Streaming](#adaptive-streaming) over HTTP. An industry driven
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adaptive streaming protocol. It is defined by ISO/IEC 23009, which can be found
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on the
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[ISO Publicly Available Standards page](https://standards.iso.org/ittf/PubliclyAvailableStandards/).
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###### DRM
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Digital Rights Management.
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For more information, see the
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[Wikipedia page](https://en.wikipedia.org/wiki/Digital_rights_management).
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###### Gapless playback
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Process by which the end of a [track](#track) and/or the beginning of the next
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track are skipped to avoid a silent gap between tracks.
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For more information, see the
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[Wikipedia page](https://en.wikipedia.org/wiki/Gapless_playback).
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###### HEVC
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High Efficiency Video Coding, also known as the H.265 video [codec](#codec).
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###### HLS
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HTTP Live Streaming. Apple’s [adaptive streaming](#adaptive-streaming) protocol.
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For more information, see the
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[Apple documentation](https://developer.apple.com/streaming/).
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###### Manifest
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A file that defines the structure and location of media in
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[adaptive streaming](#adaptive-streaming) protocols. Examples include
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[DASH](#dash) [MPD](#mpd) files, [HLS](#hls) multivariant playlist files and
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[Smooth Streaming](#smooth-streaming) manifest files. Not to be confused with an
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AndroidManifest XML file.
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###### MPD
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Media Presentation Description. The [manifest](#manifest) file format used in
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the [DASH](#dash) [adaptive streaming](#adaptive-streaming) protocol.
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###### PCM
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Pulse-Code Modulation.
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For more information, see the
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[Wikipedia page](https://en.wikipedia.org/wiki/Pulse-code_modulation).
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###### Smooth Streaming
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Microsoft’s [adaptive streaming](#adaptive-streaming) protocol.
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For more information, see the
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[Microsoft documentation](https://www.iis.net/downloads/microsoft/smooth-streaming).
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###### Track
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A single audio, video, text or metadata stream within a piece of media. A media
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file will often contain multiple tracks. For example a video track and an audio
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track in a video file, or multiple audio tracks in different languages. In
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[adaptive streaming](#adaptive-streaming) there are also multiple tracks
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containing the same content at different bitrates.
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## General - Android ##
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###### AudioTrack
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An Android API for playing audio.
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For more information, see the
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[Javadoc](https://developer.android.com/reference/android/media/AudioTrack).
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###### CDM
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Content Decryption Module. A component in the Android platform responsible for
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decrypting [DRM](#drm) protected content. CDMs are accessed via Android’s
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[`MediaDrm`](#mediadrm) API.
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For more information, see the
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[Javadoc](https://developer.android.com/reference/android/media/MediaDrm).
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###### IMA
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Interactive Media Ads. IMA is an SDK that makes it easy to integrate multimedia
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ads into an app.
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For more information, see the
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[IMA documentation](https://developers.google.com/interactive-media-ads).
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###### MediaCodec
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An Android API for accessing media [codecs](#codec) (i.e. encoder and decoder
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components) in the platform.
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For more information, see the
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[Javadoc](https://developer.android.com/reference/android/media/MediaCodec).
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###### MediaDrm
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An Android API for accessing [CDMs](#cdm) in the platform.
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For more information, see the
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[Javadoc](https://developer.android.com/reference/android/media/MediaDrm).
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###### Audio offload
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The ability to send compressed audio directly to a digital signal processor
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(DSP) provided by the device. Audio offload functionality is useful for low
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power audio playback.
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For more information, see the
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[Android interaction documentation](https://source.android.com/devices/tv/multimedia-tunneling).
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###### Passthrough
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The ability to send compressed audio directly over HDMI, without decoding it
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first. This is for example used to play 5.1 surround sound on an Android TV.
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For more information, see the
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[Android interaction documentation](https://source.android.com/devices/tv/multimedia-tunneling).
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###### Surface
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See the [Javadoc](https://developer.android.com/reference/android/view/Surface)
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and the
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[Android graphics documentation](https://source.android.com/devices/graphics/arch-sh).
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###### Tunneling
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Process by which the Android framework receives compressed video and either
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compressed or [PCM](#pcm) audio data and assumes the responsibility for
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decoding, synchronizing and rendering it, taking over some tasks usually handled
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by the application. Tunneling may improve audio-to-video (AV) synchronization,
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may smooth video playback and can reduce the load on the application processor.
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It is mostly used on Android TVs.
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For more information, see the
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[Android interaction documentation](https://source.android.com/devices/tv/multimedia-tunneling)
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and the
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[ExoPlayer article](https://medium.com/google-exoplayer/tunneled-video-playback-in-exoplayer-84f084a8094d).
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## ExoPlayer ##
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{% include figure.html url="/images/glossary-exoplayer-architecture.png" index="1" caption="ExoPlayer architecture overview" %}
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{% include figure.html url="/images/glossary-rendering-architecture.png" index="1" caption="ExoPlayer rendering overview" %}
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###### BandwidthMeter
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Component that estimates the network bandwidth, for example by listening to data
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transfers. In [adaptive streaming](#adaptive-streaming), bandwidth estimates can
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be used to select between different bitrate [tracks](#track) during playback.
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For more information, see the component
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[Javadoc](https://exoplayer.dev/doc/reference/com/google/android/exoplayer2/upstream/BandwidthMeter.html).
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###### DataSource
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Component for requesting data (e.g. over HTTP, from a local file, etc).
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For more information, see the component
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[Javadoc](https://exoplayer.dev/doc/reference/com/google/android/exoplayer2/upstream/DataSource.html).
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###### Extractor
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Component that parses a media [container](#container) format, outputting
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[track](#track) information and individual [access units](#access-unit)
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belonging to each track suitable for consumption by a decoder.
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For more information, see the component
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[Javadoc](https://exoplayer.dev/doc/reference/com/google/android/exoplayer2/extractor/Extractor.html).
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###### LoadControl
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Component that decides when to start and stop loading, and when to start
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playback.
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For more information, see the component
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[Javadoc](https://exoplayer.dev/doc/reference/com/google/android/exoplayer2/LoadControl.html).
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###### MediaSource
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Provides high-level information about the structure of media (as a
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[`Timeline`](#timeline)) and creates [`MediaPeriod`](#mediaperiod) instances
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(corresponding to periods of the `Timeline`) for playback.
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For more information, see the component
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[Javadoc](https://exoplayer.dev/doc/reference/com/google/android/exoplayer2/source/MediaSource.html).
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###### MediaPeriod
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Loads a single piece of media (e.g. audio file, ad, content interleaved between
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two ads, etc.), and allows the loaded media to be read (typically by
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[`Renderers`](#renderer)). The decisions about which [tracks](#track) within the
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media are loaded and when loading starts and stops are made by the
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[`TrackSelector`](#trackselector) and the [`LoadControl`](#loadcontrol)
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respectively.
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For more information, see the component
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[Javadoc](https://exoplayer.dev/doc/reference/com/google/android/exoplayer2/source/MediaPeriod.html).
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###### Renderer
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Component that reads, decodes and renders media samples. [`Surface`](#surface)
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and [`AudioTrack`](#audiotrack) are the standard Android platform components to
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which video and audio data are rendered.
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For more information, see the component
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[Javadoc](https://exoplayer.dev/doc/reference/com/google/android/exoplayer2/Renderer.html).
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###### Timeline
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Represents the structure of media, from simple cases like a single media file
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through to complex compositions of media such as playlists and streams with
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inserted ads.
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For more information, see the component
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[Javadoc](https://exoplayer.dev/doc/reference/com/google/android/exoplayer2/Timeline.html).
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###### TrackGroup
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Group containing one or more representations of the same video, audio or text
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content, normally at different bitrates for
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[adaptive streaming](#adaptive-streaming).
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For more information, see the component
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[Javadoc](https://exoplayer.dev/doc/reference/com/google/android/exoplayer2/source/TrackGroup.html).
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###### TrackSelection
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A selection consisting of a static subset of [tracks](#track) from a
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[`TrackGroup`](#trackgroup), and a possibly varying selected track from the
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subset. For [adaptive streaming](#adaptive-streaming), the `TrackSelection` is
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responsible for selecting the appropriate track whenever a new media chunk
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starts being loaded.
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For more information, see the component
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[Javadoc](https://exoplayer.dev/doc/reference/com/google/android/exoplayer2/trackselection/TrackSelection.html).
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###### TrackSelector
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Selects [tracks](#track) for playback. Given track information for the
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[`MediaPeriod`](#mediaperiod) to be played, along with the capabilities of the
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player’s [`Renderers`](#renderer), a `TrackSelector` will generate a
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[`TrackSelection`](#trackselection) for each `Renderer`.
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For more information, see the component
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[Javadoc](https://exoplayer.dev/doc/reference/com/google/android/exoplayer2/trackselection/TrackSelector.html).
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