Video Terms Flashcards
AAC (Advanced Audio Coding)
Advanced Audio Coding (AAC) is a commonly used audio compression codec developed by MPEG. It is the most commonly supported audio codec and is available in every major browser and device. There are two common versions of AAC: AAC-LC (Low complexity) and AAC-HE (High Efficiency).
ABR (Adaptive Bitrate)
Adaptive Bitrate (ABR) is a content streaming technique which allows multiple different video renditions in different resolutions and bitrates to be made available to a video player. Players can then use client side bandwidth estimations to decide which is the best rendition to use given the current available bandwidth. ABR is used on the pretense that reducing the visual quality to the viewer is more important than the user experiencing buffering.
AC-3 also known as Dolby Digital
An audio codec developed by Dolby Laboratories. Also known as AC-3. It’s commonly available in living room devices but usually not in web browsers or mobile devices.
AOM (Alliance for Open Media)
AOM stands for the Alliance for Open Media which is an organization founded by Google, Intel, Amazon Nvidia, Netflix, and Mozilla, among others. AOMs goal is to provide royalty free media technologies for use on the open internet. Likely a response to the unclear licensing requirements on the HEVC codec, their first effort being the AV1 video codec.
AV1
Alliance Video Codec version 1 is a royalty free video compression codec developed by AOM. AV1 is the spiritual successor to the VP (specifically VP9) line of codecs. While AV1 is very new, many, but not all evergreen browsers, have already added support for decoding. However, support in mobile devices is still lacking. AV1 provides exceptional video quality at very low bitrates, but is extremely computationally expensive to encode. It is therefore not suitable (at least for now) for live video encoding, and only economical in environments where a single video receives a large number of views by offsetting the high encoding cost with bandwidth savings.
AVC (Advanced Video Coding) H.264
Advanced Video Coding (AVC), also known as H.264, is a video codec developed by MPEG. It is the most commonly supported video codec on the planet and is available in every major browser and device. It is comparatively cheap to encode and decode.
Aspect Ratio
Aspect ratio refers to the ratio of the width and height dimensions of a video. You can calculate the ratio by dividing the width and height by the greatest common divisor of both.
For a video that is 1920 pixels wide and 1080 pixels in height, the greatest common divisor is 120, resulting in an aspect ratio of 16:9.
The two most common aspect ratios for video are 4:3 (e.g. 640x480) and 16:9 (1920x1080 or 1080p). With vertical video, popular for mobile device recording, the common aspect ratio numbers get reversed and 16:9 becomes 9:16.
The square aspect ratio, 1:1, is also becoming popular because of social sites like Instagram that allow square video as an option.
Beacon
In the streaming video context, beacon often refers to sending analytics data from a client application to an analytics service. This often comes in the form of an HTTP GET request with the data encoded as URL query variables, or as a POST request with the data in the body of the request.
For example with Mux Data, which tracks the quality of experience of video players, the Mux client SDKs sends beacons of data to Mux servers to track when player errors and other issues occur.
Bitrate
Bitrate, in a generic sense, represents the number of bits that can be (or need to be) sent per second within a stream of data. In the video space, bitrate refers to the number of bits used per second of content within an encoded video.
Buffering
Buffering is the term given to the end user experience of waiting for enough video content to have been downloaded for playback to start or continue. This can happen mid-playback if sufficient bandwidth is not available to stream the content. Buffering is often represented visually with a spinning circle. It is considered to be the biggest single cause of abandoned playback sessions by viewers.
CBR (Constant Bitrate)
CBR, or Constant Bitrate, describes a method of encoding where the continuous bitrate of the video remains constant as it plays. This is in comparison to VBR, or Variable Bitrate encoding. CBR can be valuable in live streaming where dramatic changes in the bitrate of the stream could cause the player to fall behind and stall.
CDM (Content Decryption Module)
A Content Decryption Module (CDM) is a proprietary piece of software embedded in a web browser that is used to decrypt encrypted (DRM) content. It works as a “black box”, receiving keys and encrypted content and returning decrypted content. It can be interacted with via the Encrypted Media Extensions (EME) API in browsers.
CDN (Content Delivery Network)
A Content Delivery Network (CDN) is a global network of servers where local copies of a file are stored to increase the delivery speed of that file to nearby users. For example if a user is in Japan viewing a video that is hosted in the eastern US, it can be very slow to load that video. If a CDN is in use, the CDN would instead copy (or “cache”) the video onto a server in or near Japan, so that it can be loaded much more quickly.
CDNs only cache a file after its been requested by a user, and only store the cached copy for a limited amount of time. This means delivering the file may still be slow the first time a file is requested, and after long periods where no user requests the file. However, CDNs do still help in this case by optimizing the route of the file from the origin (where the original file is hosted) to the edge (the server close to the user). CDNs can pick delivery routes that avoid internet congestion, similarly to how Google Maps helps you avoid traffic.
The decision of which server to load a file from happens dynamically behind the scenes, so the same URL can be used for users all around the world.
Common CDNs include Akamai, Fastly, Limelight, Level3, CloudFront, StackPath and many others.
CENC
MPEG Common Encryption (CENC) is an MPEG standard for the storage of encrypted video and audio content within the ISOBMFF file format. CENC allows content to be protected against multiple DRM Schemes (Playready, Widevine etc.) but only stored once.
Cache
Cache refers to storing data for quicker access at a later time. The word can be used as a noun (e.g. “the cache of data”) or a verb (e.g. “cache the data”).
Video data can be cached at a number of points in the delivery pipeline. CDNs cache video data in edge servers closer to users. Web browsers cache the results of requests for video data so that later requests for the same data can pull from the browser’s memory.
Clipping
Clipping is taking a smaller segment or clip of an existing video and creating a new stand-alone video. Clipping is often used to grab a sports highlight from a longer game recording, or a quick trailer from a movie or longer piece of content.
Codec
Codec is a portmanteau combining the words “coder” and “decoder.” A codec is a specification that describes a method for representing information. In digital media, codec typically refers to a method of encoding audio, video (and sometimes text and other metadata) in a compact fashion for transmission and storage. Codecs may be lossless, where the decoder is capable of reproducing the original content exactly, or lossy where the decoder can only reproduce an approximation of the original content. Lossy codecs use significantly less storage and bandwidth, but produce lower fidelity media. Sometimes the word codec is used to describe a specific implementation of a coder or decoder. x264 for example is an encoder implementation of the h.264 video compression standard.
Content Management System (CMS)
CMS is an initialism meaning “Content Management System”, which typically describes a user interface for organizing collections of content. A CMS can be specific to any kind of content, such as a blog, but a feature specific to many online video platforms is that they also provide a proprietary content management system specific to their asset library.
DAM (Digital Asset Management)
DAM is an initialism for Digital Asset Management. DAMs are responsible for managing digital assets, including storage, sharing, and organization. Some compare a DAM to a specialized CMS that focuses only on digital asset such as videos and images.
DASH / MPEG DASH
MPEG DASH (Dynamic Adaptive Streaming over HTTP) is an implementation of an adaptive bitrate (ABR) streaming technology designed by MPEG. It uses a single XML-based manifest file usually delivered with the .mpd file extension. It is commonly used with fMP4 media fragments. It is often used when delivering DRM’d content since it is easy to interchange with CENC encrypted media.
DRM (Digital Rights Management)
Digital Rights Management (DRM) is the process of protecting content such that it can only be played with certain restrictions. These restrictions might include a period of time in which the content can be played or set limitations on the hardware security features available on the device which is playing the content. The most common DRM technologies are Apple’s Fairplay, Google’s Widevine, and Microsoft’s Playready.
DRM License
When playing back a DRM-protected video, the client must first retrieve a DRM license. This license specifies the restrictions to playback the content, such as an expiration time, any geographic restrictions, or even device-specific restraints such as HDCP.
Decoding
Decoding is the process of converting compressed data back into a presentable format. For streaming video, the raw video frames are encoded into a compressed data stream and then decoded in order to convert the compressed data back into playable video frames. Decoding is the inverse of encoding.
Demultiplexing / Demuxing
Demultiplexing (a.k.a. demuxing) is the process of extracting each individual signal from within a single stream, where these signals have previously been combined via multiplexing.
