On Leaps and DASHes2/27/2012 12:01 AM Eastern
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-fitsall
way to do adaptive bit-rate video
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
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
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.