Video
Standards-Based, Premium Content for the Modern Web
How Premium Video Content Streams over the Internet
These days, a person is just as likely to be watching a movie on their laptop, tablet, or mobile phone, as they are to be sitting in front of a television. Cable operators are eager to provide premium video content to these types of devices but there are high costs involved in supporting the wide array of devices owned by their customers. A multitude of technological obstacles stand in the way of delivering a secure, high-quality, reliable viewing experience to the small-screen. This four-part blog series describes an open, standards-based approach to providing premium, adaptive bitrate, audio/video content in HTML and how open source software can assist in the evaluation and deployment of these technologies.
Part 1 - Open Web Standards: Encrypted Media Extensions (EME)
HTML5 extension APIs enable JavaScript applications to facilitate encryption key requests between a DRM-specific Content Decryption Model (CDM) embedded in the browser and a remote license server. Using EME, the app may choose between multiple DRM systems available in the browser to meet the requirements of both the content and its legal distribution rights. The mechanism by which each DRM conducts its business is opaque to the application since it simply functions as a proxy for messages to and from the license server.
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Part 2 - Streaming Media Formats: Adaptive Bitrate (ABR) Media and MPEG-DASH
In the world of streaming video, a provider’s worst nightmare is the infamous “buffering circle” animation. On slower network connections, devices will not be able to download media segments for high-resolution, high-bitrate video fast enough to prevent the player from buffering. Adaptive Bitrate (ABR) media formats were designed to alleviate this problem by chopping the media up into segments, providing multiple resolutions and bitrates for each segment, and then allowing the client application to choose which segment to download based on current network conditions. Multiple ABR formats exist today, but we will focus on the MPEG open standard, Dynamic Adaptive Streaming over HTTP (DASH). While the main DASH specification enables a vast array of media and manifest choices, several standards bodies (like the DASH Industry Forum) have been established to define subsets of DASH that make it easier to implement and test deployable solutions.
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Part 3 - Web Media Playback: dash.js
The W3C Media Source Extensions (MSE) and Encrypted Media Extensions (EME) APIs provide all the tools necessary to play adaptive bitrate, premium video content in modern web browsers. However, we still need sophisticated HTML/JavaScript applications that can make use of these APIs. What began as a reference implementation for the Dash Industry Forum’s interoperability specification, the dash.js open source media player has since been adopted as the basis for several commercial applications. dash.js contains a configurable adaptation rules engine and full support for encrypted content playback using EME on a variety of browsers and operating systems.
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Part 4 - Tools for Creating Premium Content: Content Creation with CommonEncryption
The ISO CommonEncryption standard specifies a single encryption mechanism (AES-128) and a limited selection of block modes for protected content. No matter the mechanism used to obtain decryption keys, a media engine that recognizes the CommonEncryption format and has access to the keys can decrypt the media samples contained within. In addition to the cipher algorithm and block mode, the CommonEncryption specifications indicate how DRM-specific data may be carried within the media to assist in the retrieval of decryption keys. CableLabs has developed open-source tools that can be used to create encrypted, MPEG-DASH content for several commercial DRM systems supported by EME browsers today.
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Greg Rutz is a Lead Architect at CableLabs working on several projects related to digital video encoding/transcoding and digital rights management for online video.