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