What Is MPEG-DASH?

8th May, 2019 by

MPEG-DASH is a name befitting a cartoon superhero, as well as a history to match. Its story of origin is an unusual tale of collaboration and cooperation among companies normally locked in mortal combat, while this adaptive bitrate streaming technique has performed heroics on behalf of internet users weary of incompatible file types and playback error messages.

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Like many aspects of the internet, video files weren’t regulated or standardised in the 1990s. The limitations of internet bandwidth and the scramble to secure a place in this new world order led to dozens of incompatible display techniques, all attempting to squeeze media files down dial-up phone lines. There were incompatible codecs, proprietary file formats, and players from the likes of Macromedia, Microsoft, and RealPlayer. Each program would play some file types but not others, requiring consumers to install various packages onto each web-enabled device. Even worse, codecs regularly stopped working or conflicted with one another, leading to videos playing without pictures and hexadecimal error messages.

The challenge of displaying moving images at a recognised standard had already been tackled by the creation of a Moving Picture Experts Group in the late 1980s. Founder members including Samsung, Microsoft, and Dolby had developed a number of international protocols for compressing, decoding, and processing moving images. MPEG-1 debuted in 1992 and spawned a number of evolutionary sequels, but these failed to achieve universal adoption on the free-for-all internet.

Got to dash

By the Noughties, MPEG members were openly discussing a streaming media delivery system which would work on as many devices as possible. The result of these lengthy negotiations was the development of Dynamic Adaptive Streaming over HTTP. Using the HyperText Transfer Protocol already familiar to internet users, this international standard was intended to make sure that consumers enjoyed a comparable media experience on any device, anywhere. When MPEG-DASH finally debuted in 2010, the plethora of web-enabled devices ranged from games consoles and web-enabled TVs to phones and tablets.

MPEG-DASH was swiftly adopted as the video codec of choice by almost everyone. Apple continued championing their proprietary HTTP Live Streaming protocol, despite having contributed to MPEG-DASH’s development. Even so, both systems operated on very similar principles. A file was split into bite-sized chunks, to be dispatched chronologically on request from a server. Each segment was saved at different bit rates, offering variations in quality and file size. Host servers would dispatch the highest-resolution version suitable for connection speeds at that precise instant, ensuring consumers enjoyed the best possible picture quality at all times. This also enabled the display device to quickly buffer at low-resolution before increasing the pixel count once connection speeds increased. The result was rapid playback, albeit characterised by pixellation during the first few seconds of footage.

A world of difference

Unlike the proprietary and incompatible formats that preceded it, MPEG-DASH is codec-agnostic. That means it works on most devices without requiring codec installations. More importantly, it gave web developers and media companies a recognised standard to adhere to. It offers consumer-oriented services like closed captioning, supporting both multiplexed and non-multiplexed video and audio tracks. It displays at different screen resolutions and can carry different soundtracks, including descriptive audio for visually-impaired audiences.

However, perhaps MPEG-DASH’s greatest attribute is its compatibility with HTML5. This modern-day web design and development protocol is designed to create a Write Once Run Anywhere standard for web pages and internet content. By dovetailing with this, and by minimising issues like packet loss and jitter, DASH delivers consistent media playback on almost any device. It’s something web users in the Nineties could have only dreamed of.

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