With so many different formats currently being used to deliver video content to mobile devices, it might seem logical to question why another new format is necessary. With Apple championing HLS (HTTP Live Streaming), Adobe providing HDS (HTTP Dynamic Streaming) and Microsoft advocating Smooth Streaming, it may seem as if there are already enough formats to satisfy even the most rarefied technology requirement. The DASH (Dynamic Adaptive Streaming over HTTP) format is a somewhat late entrant to the marketplace and has been slow to gain traction. But that could be changing due to efforts by the DASH Industry Forum (DASH-IF) and large vendors like Adobe. Also, since DASH is an international standard that is not under control of a single vendor, it stands a good chance of gaining widespread adoption in the long run.
Wowza Media Server 3 demo, Silverlight Smooth Streaming VOD
What DASH Is ... And What It’s Not
ISO, the International Standards Organization, formally approved MPEG-DASH (ISO/IEC 23009-1) in April 2012, although work had been going on long before then. The standard is designed to formalize the video delivery technique called HTTP streaming that has been developed by several different companies over the past half-decade.
DASH is designed to get around problems caused by firewalls and wildly varying network bandwidths. The technology relies on the viewing device (user’s mobile phone, tablet, PC, Roku, etc.) to control the rate at which media signals are retrieved from a server.
This ability to adapt dynamically to changes in the network, cleverly called adaptive bit rate (ABR) streaming, is one of the key features of DASH systems. Another feature is that video streams are broken into a series of small files that can be delivered by standard web servers through normal Internet infrastructure using the universally supported HTTP protocol. This helps avoid problems that other types of streaming protocols (such as RTP) had with firewalls and with servers having to manage video delivery rates to thousands of devices simultaneously.
To clarify DASH’s role in video delivery, it is important to explain what DASH is not.
- DASH is not a codec like MPEG or JPEG; rather, it is designed to support delivery of video signals that have been compressed with these standards.
- DASH is not a container format like MP4 or AVI; rather, it is a formalized way to deliver video within these standard container types.
- DASH is not a markup language like HTML5 or a protocol like HTTP; instead, DASH provides a standard way to represent and describe video files that can be transported across the Internet.
Openness and flexibility are key aspects of the DASH specification, although this can be both a blessing and a curse. Its versatility makes it suitable for a range of applications and bit rates, from low-resolution webcams to high-definition sports broadcasts. DASH supports multiple codecs, multiple digital rights management (DRM) systems and multiple container formats. However, with all of these possibilities, it is difficult to get agreement among vendors on a common selection of these technologies that would permit widespread interoperability.
Path 1’s DASH-based PiXiE Encoder-Decoder
Bart Schade, founder and chief technology officer of Path 1, demonstrated the DASH-based PiXiE Encoder-Decoder for contribution applications during IBC 2013. On the dynamics of the DASH marketplace, he says, “One thing that could really drive the adoption of DASH for consumer video delivery is a democratic ad insertion and auditing mechanism that is supported by major vendors like Adobe.”
He continues, “If our industry can agree on a set of codecs, wrappers and DRM that allows advertisements to be inserted at any point in the OTT distribution chain between a content provider and a viewer, it will revolutionize the economics of Internet video.”
Adobe’s Path Forward
Current DASH-IF members
Adobe Flash is probably the most widely used IP video delivery format today, with desktop/laptop penetration rates in excess of 95 percent, according to several industry sources. However, Adobe’s share of the mobile market is much lower due to Apple’s refusal to support Flash on iOS devices. The latter factor may have led to a Feb. 27, 2012, statement by Kevin Towes on his Adobe blog that “Adobe’s video solutions will adopt the emerging video standard MPEG-DASH across our video streaming, playback, protection and monetization technologies.” This is a pretty definitive statement of intent, though the timing of DASH support was not indicated.
(Adobe’s Ashley Still, director of product management, said in a recent interview with Beet.tv that Adobe’s support of MPEG-DASH would begin in “early 2014.”)
Brian Isaacson, president of Communitek Video Systems and an Adobe authorized reseller, says, “Although I have not yet seen support for MPEG-DASH technology within Adobe Media Server [as of version 5.0.3], I look forward to an official release in the near future. I’d like to see Adobe add this, as I’m starting to hear from clients asking for this capability, particularly for delivery to Android mobile devices.”
It remains to be seen when Adobe will actually roll out support for DASH technology. Additional, complementary technologies are being developed alongside DASH, including HEVC (H.265) and Ultra HD (4K). In fact, the argument could be made that all three of these technologies will be needed for the next generation of video streaming. So hold onto your seats and see what happens when Adobe and the rest of the market DASH into the future.