Key concepts and terms

Familiarize yourself with some common terms related to streaming media.

FormatFile typeDescriptionExtensionExample
Apple HTTP Live Streaming (HLS)Alternate Audio RenditionA playlist file that enables an alternate representation of the audio data to be played along with the main video content. It's listed via the #EXT-X-MEDIA tag in the Master Playlist and it allows the player to switch to a different audio language track or surround sound playback.N/AN/A
HLSAudio-Only Variant StreamA playlist file that can be played independent of other playlists containing video data. It is listed via the #EXT-X-STREAM-INF tag in the Master Playlist and allows the player to switch to an audio-only playback when bandwidth is constrained.N/AN/A
HLSMaster PlaylistContains a list of all the requested stream's available bitrates (tracks). For HLS Ingest, the player requests this file just once at the start of the session. Also includes each track's bandwidth, so the player uses this information to switch between the most appropriate bitrates in case of network bandwidth fluctuations..m3u8.master.m3u8
HLSMedia PlaylistContains a list of media segments. When they're played sequentially, they make up a multimedia presentation. For a live stream, the player requests this file frequently to get the next set of segments for playback. The encoder includes an end-of-stream marker. When the player receives this, it stops requesting the file and also stops playback (after running through its buffer)..m3u8index_1000kpbs.m3u8
HLSSegmentOne or more tracks, including video, audio, or audio mixed with video or subtitles. Video segments use the MPEG2-TS file format. Audio-only segments can be either in MPEG2-TS or packed audio format (.aac)..ts or .aacsegment10.ts
HLSEncryption KeyIncludes a 128-bit key used to encrypt the segments. It is only requested when encryption is turned on at the encoder..keycrypt.key
Dynamic Adaptive Streaming over HTTP (DASH)MPDMedia presentation description. Equivalent to the master playlist in HLS. MPD provides sufficient information for a DASH client for adaptive streaming of the content by downloading the media segments from an HTTP server. Each MPD has one or more Adaptation sets. An Adaptation set is a collection of segment representations. There is no equivalent for this in HLS. There is no separate file store for Adaptation set; it resides in the MPD. For details, refer to [DASH}9dash).mpdgame_ finals_2015.mpd
Common Media Application Format (CMAF)CMAF IngestCommon Media Application Format (CMAF) is a new MPEG standard for packaging content in the ISO Base Media File Format (ISOBMFF) format. Both DASH and HLS formats can now reuse the same set of audio/video files to target Apple and non-Apple devices, resulting in a simplified content preparation workflow and reduced storage and delivery costs for customers. For details, see CMAF.N/AN/A
Adobe HTTP Dynamic Streaming (HDS)Set-Level ManifestA manifest document that describes only set-level details of a set of content renditions, such as bitrates, screen resolution, and language. A set-level manifest refers to the details of individual renditions via a URL reference. This is equivalent to master.m3u8 in HLS..f4mtennis_all.f4m
HDSStream-Level ManifestA manifest document that describes the details of a single content rendition (as opposed to describing the details of all renditions that make up a set)..f4mtennis_ 1000kbps.f4m
HDSManifest FileA file conforming to the Flash Media Manifest specification that is used to describe a presentation..f4mtennis.f4m
HDSFragmentA fragment is a named downloadable entity that contains the audio or video data for a given interval of the presentation. For example, a fragment of a video rendition might contain the video data for a short sequence of video frames corresponding to a four-second interval of time. Although audio and video fragments are the most common types of fragments; fragments may contain data other than audio or video data. Fragments are identified by a number. There is an equivalent to HLS segment size..f4ftennis_1000kbps_1.f4f
HDSSegmentA contiguous group of content fragments. In HDS, segments are the largest unit of content and are used to improve storage and cache efficiency. This is the entire file duration, specified by the sum of all segment durations.N/AN/A