Picture Perfect: MPEG-DASH Basics
Those of us old enough to remember the 1990s will recall the challenges of viewing video content online. From proprietary formats like RealPlayer to platform-specific file types such as QuickTime, consumers occasionally had to download an entire software package to play a single file. Even if the file did display, there was no control over its quality, while primitive line speeds made streaming media seem like an unattainable goal.
MPEG-DASH represents a remarkable evolution from the days of incompatible and inefficient file formats. This adaptive bitrate streaming platform was developed to an international standard, with its interoperability defined by eight charter members, and over 60 associate or contributor members. The former include Microsoft, Samsung and Dolby, while Google, Netflix, and Verizon are among the latter. The aim of this unprecedented collaboration was to ensure that consumers around the world enjoyed the near-identical multimedia experience, regardless of their hardware choice, operating system or connection speed.
MPEG-DASH Core principles
One of the few major tech firms missing from MPEG-DASH’s current member’s list is Apple, though they were involved in its original development. Apple continues to use its own HTTP Live Streaming protocol, mimicking its rival’s method of operation. In this process, a media file is subdivided into numerous small segments, each of which is recorded at several bit rates.
These are distributed to consumer devices in chronological order, while the sender automatically selects the highest-quality version suitable for real-time bandwidth fluctuations. This explains the tendency for a video clip to look pixelated during initial playback, before quickly settling into a smoother picture. Lower-quality file snippets will be distributed if the host detects bandwidth issues, or if an established buffer of up-next segments begins to deplete.
The second part of MPEG-DASH’s name is an abbreviation of Dynamic Adaptive Streaming over HTTP. It is distributed using the HTTP protocol powering the internet. This means that it works on almost any device, from smartphones and tablets to internet-enabled TVs or games consoles. Indeed, the recent explosion of hardware capable of playing streaming media content ensured DASH’s 2010 launch was well-timed. It built and expanded on the Moving Pictures Experts Group format, pioneered in 1988 and publicly debuted five years later. Rather like the standard created by the Joint Photographic Experts Group, MPEG was always intended as a universal format, but it took almost twenty years of competition before it became an industry standard.
Reasons to be cheerful
Below are some of the advantages of MPEG-DASH over other video streaming formats:
- It’s codec-agnostic, so consumers don’t have to endure “a codec is required to play this file” messages anymore. Compatible coding formats range from Google’s open source VP9 to the intensive data compression of HEVC (also known as H.265).
- Although the founders of DASH admit it is “no magic panacea for the fragmentation problems of media, devices and markets”, it gives developers and programmers a widely-recognized platform with a guaranteed future of evolution, not revolution.
- DASH is compatible with multiplexed and non-multiplexed video and audio tracks, making it a one-size-fits-all solution when firms want to provide multiple files. Variants might include different screen resolutions, languages or even audio options.
- Closed captioning is integrated, supported using a format developed by the same W3C consortium which regulates internet development. Timed Text Markup Language is used to display interpretative information as subtitles or descriptions.
- It’s been designed with HTML5 compatibility in mind. As HTML evolves towards a single universal Write Once Run Anywhere standard, it’s vital to have a multimedia format offering equal compatibility with consumer hardware and software.