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A Simple Streaming Glossary

The meaning of some common terms you’ll hear

A recent Radio World ebook explores the world of streaming for radio. In this excerpt David Bialik lays out some commonly heard terms.

The following may help you navigate the language around streaming. It is not intended to be comprehensive but to give you a head start in this growing medium with new technology emerging daily.

  • AAC — Audio Coding, an audio coding format for lossy digital audio compression. Usually preferred Advanced over MP3, it promises comparable or better quality at lower bitrates. AAC has been standardized by ISO and IEC as part of the MPEG-2 and MPEG-4 specifications.
  • Ad Delivery Network — An on-demand file serving network that can deliver commercial content for the streamer.
  • Ad Replacement — When ads broadcast over the air are replaced with different content on the stream.
  • AES TD1004 — The Audio Engineering Society’s Recommendation for Loudness of Audio Streaming and Network File Playback. These recommendations primarily are intended for “radio-like” mono and stereo streams.
  • Bitrate — Bitrate = Sample rate X bits per sample used to encode the music. The number of bits per sample also depends on the number of audio channels.
  • CDN — Content Delivery Network, a scalable distributer of streams.
  • Client-Side Ad Insertion (CSAI) — Advertising that only happens within the website or app streaming your content. Banners, video pre-rolls, other items specific to a player or page.
  • CMAF — A container format (see below).
  • Codec — Digital audio compression algorithm used.
  • Container Format — Otherwise known as a wrapper, this may contain the audio and video plus all the associated metadata (i,e. MP4, CMAF). The container carries the payload (audio, video, or data files).
  • Cuepoint — A marker residing in the metadata, triggering a new action.
  • Decoder — A component that is part of the player, used to reassemble the content.
  • Direct Ad Insertion (DAI) — Personalized ad replacement that is unique to the listener. This can be based on listener location, browsing preferences, etc.
  • Encoder — The system used to take the content and send it to the stream, usually by compressing your linear audio into an MP3 or AAC stream.

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  • Encoding Format — The method of converting to a digital format (i.e., AAC, MP3)
  • FLAC — Free Lossless Audio Codec, a compressed audio format with no loss of quality.
  • FLV — Flash Video Format, a container file format used to deliver digital video content over the internet via Adobe Flash Player.
  • HE-AAC / HE-AAC v2 / AAC+ — “High-Efficiency AAC,” a lossy audio codec for low bit rate streaming, expanding on the quality vs. size gains made by standard AAC.
  • HLS — HTML Live Streaming, a high-quality transport format used by Apple.
  • Icecast — A streaming media project released as free software, maintained by the Foundation.
  • ID3 or ID3 tag — A metadata format that stores information (Title, Artist, etc.). This may be called the data container.
  • Injected content — Content from another source, usually replacing other content.
  • Interstitial — One or more recorded elements used in stream production (i.e., bumpers, jingles, promos, etc.)
  • LKFS — “Loudness, K-weighted, relative to full scale.” A standard loudness measurement. Sometimes referred as LUFS.
  • Lossless Streams — A high-bitrate non-compressed stream.
  • Lossy Streams — Digitally compressed sampled streams (i.e., MP3/AAC).
  • LUFS — “Loudness units relative to full scale,” synonymous with LKFS.
  • Metadata — The data stream that accompanies the media content. This can hold the “Now Playing” information, commercial cues, time code or any other information needed to play the stream.
  • MP3 — An audio coding format for lossy digital audio compression developed by Fraunhofer and Bell Labs. This supports very low bit rates.
  • MP4 — One of the earliest digital video file formats. Can be used for high-quality video or audio while maintaining relatively small file sizes.
  • MPEG-DASH — Dynamic Adaptive Streaming over HTTP, an adaptive bitrate streaming technique that allows for high quality of content. This is comparable to HLS.
  • Now Playing Information — “What the stream is playing” can be displayed, usually sent by metadata.
  • Ogg — A container format.
  • Ogg Vorbis — An audio coding format with lossy audio compression.
  • Player — The program used on the audience side to play the content; it could be an app.
  • Podcast — A digital audio file that can be downloaded to a personal device and/or player.
  • RTMP — Real Time Messaging Protocol, a TCP-based protocol that maintains persistent connections and also allows communication with low latency. This allows for a stream to be delivered correctly.
  • Server-Side Ad Insertion (SSAI) — Advertising added to audio as it is streamed or delivered, rather than from the studio playout. Ads become part of the audio itself.
  • Shoutcast — A software application that allows anyone to stream audio over the internet.
  • Total Line Reporting — When the stream and over-the-air product are the same and no segments are substituted.
  • Transport Format — How the stream is delivered (e.g. HLS, Icecast, rtmp)
  • xHE-AAC — A lossy audio codec for low bit rate streaming. It also is used by Digital Radio Mondiale (DRM).

David Bialik is a consultant; co-chair of the AES Technical Committee for Broadcast and Online Delivery; and chair of the Metadata Usage Working Group at the NRSC. He is former director of stream operations for CBS Radio and Entercom.