On Leaps and DASHes


This being the week of leap year, it seems timely to check in on DASH, the standards subset of the Moving Pictures Experts Group (MPEG) focused on making a one-size-fits all way to do adaptive bit-rate video streaming.

Refresher: Adaptive bit-rate streaming exists to “right-size” a video asset for the screen that wants to play it, depending on available bandwidth. In right-sizing, each video asset necessarily becomes a file that is chunked into different sizes, rather than a linear stream of contiguous bits. Bandwidth cornucopia, send biggest file size; bandwidth anorexia, send smallest file size.

DASH stands for Dynamic Adaptive Streaming Over HTTP. So, a nested acronym. “HTTP” stands for Hypertext Transfer Protocol, the underlying language of the World Wide Web. (For the advanced class - the standard also goes by “ISO/IEC 23009-1.”)

MPEG’s video roots are deep and respectable. Nearly all digital video you see on big (TV) screens today is compressed with MPEG-2, and delivered using MPEG transport. Medium (PC, tablet) and small (smartphone) screens commonly use a more recent form of compression, known as MPEG-4. So, it is understandable and good that the global MPEG brain trust is working on ways to continually improve the mechanics of video.

What problem(s) does MPEG DASH aim to solve? Let’s start with fragmentation. If you make and distribute professional video content, you’re already working the online/TV Everywhere/IP side of the chain with more than one technique. Probably more than two: Microsoft’s Smooth Streaming, Apple’s HTTP Live Streaming (HLS) and Adobe’s Dynamic Streaming are the biggies.

Alas. All three are nearly identical, yet incompatible - a phenomenon that tends to happen when different technologies are vying for the lead, so that they become the ultimate open standard.

MPEG DASH (pronounced as the letter “M” followed by the spoken words “peg” and “dash”) hopes to assuage this. Generally speaking, it has two parts: the encoded audio and video streams, and a manifest file that identifies those streams to the client screen. DASH supports trick modes (pause, fast-forward, rewind), ad insertion and an assortment of codecs (H.264, WebM). It will be ready for deployment by midyear.

(Total aside: I am dictating this column using speech recognition software, because of an injury to my left hand. The speech recognition software keeps making a literal dash mark (-) everywhere I want to use the word “DASH.” The lesson here? Please take extra care of your appendages around all glass objects in your life.)

Unresolved issues? Intellectual property, of course. Remember MPEG-LA, which collected royalties for intellectual property in the first digital video heyday? Royalties will come into play this time around, too.

Also: Digital rights management, or DRM. While DASH does not specify a DRM, it supports certain DRM techniques as specified in other standards (namely ISO/IEC 23001-7 common encryption).

And: Whether major browser providers will incorporate DASH into their going-forward roadmaps - especially if royalty payments are involved.

As far as the big players go, MPEG DASH is supported by contributors including Apple, Adobe, Microsoft, Netflix, Qualcomm and others. However, there is a difference between being a contributor and an adopter.

That’s the latest on adaptive bit-rate streaming and MPEG DASH. And happy Leap Year to you!
Stumped by gibberish? Visit Leslie Ellis at www.translation-please.com or multichannel.com/blog.