In April 2012, ISO, the international standards body which had already given us the core media foundations of MPEG-2, MP3 and MP4, finally ratified the version of its next generation adaptive streaming standard: MPEG-DASH. In an industry besieged by three comparable (but incompatible) segmented formats many asked – why another? The participating companies in the MPEG-DASH standardization (including Microsoft, Apple, Netflix, Qualcomm, Ericsson, Samsung, and many others) saw a vision of interoperability and convergence required for large-scale market growth that trumped the proprietary and competing solutions. They replaced multiple corporation-controlled solutions with a single industry-defined open standard.
In the same spirit of cooperation in which MPEG-DASH was created, the leading streaming companies got together to form an industry forum to promote and catalyze the adoption of MPEG-DASH and help transition it from a specification into a real business. The DASH Industry Forum (DASH-IF) grew out of a grassroots DASH Promoters Group and was formally incorporated in September 2012. Today it has 67 members spread throughout the world. DASH-IF is filled with member companies who are realists about the DASH deployment challenges. DASH by itself is no magic panacea for the fragmentation problems of media, devices and markets. However, the DASH-IF members do share a common vision that the long-term benefits of convergence outweigh the costs of shorter-term efforts involved in achieving that goal. They are willing to take on the work of creating recommendations, filing bugs, and attending plug-fests and interop events, with the belief that their business and the Internet streaming market in large will benefit a great deal with convergence around DASH. The DASH-IF, representing all sectors of the streaming media ecosystem, is proactively and deterministically shaping the future and success of MPEG DASH.
The MPEG-DASH standard is attractive to many companies because of some key market benefits that it brings:
- independent stable international standard – not owned by any single company, DASH is a finalized specification and not a moving target.
- multi-video and audio tracks – deliver the complexity of a DVD or Blu-ray experience, with multiple synchronized video and audio options.
- mix of multiplexed and non-multiplexed video and audio tracks – provide for dynamic bandwidth adaptation, support for multiple audio options such as language selection and surround sound, bandwidth efficiency (sending only the requested tracks) and reduced production, storage, maintenance and delivery costs.
- common encryption – one-time encryption and packaging of content allowing simultaneous use of multiple DRM technologies.
- templated manifests – Compact manifest for fast start-up, as well as avoiding manifest download with every segment.
- non-segmented origin files – files can optionally be stored contiguously on the server and the segments accessed via byte-range requests.
- efficient ad insertion – server-based and client-based targeted ad-insertion through the use of periods.
- support for multiple CDNs/caches with the same manifest – provide flexibility to define multiple base URL in the manifest, thus improving scalability and fault tolerance
- accessibility, rating and other content descriptions – possibility of signaling content descriptions such as accessibility, rating, audio channel configuration in the manifest.
- industry convergence for streaming delivery – avoid having to provide multiple streaming solutions, each of which requires a separate ad insertion flow, content protection scheme, and a different closed captioning format.
- vibrant ecosystem – already a strong community of encoders, content packagers, delivery platforms, and player builders has been established, providing a wide range of DASH solutions.
- ease of integration – DASH will work on any HTTP server and most mainstream media servers, meaning service providers and broadcast operators are not required to buy into new vendor-specific ecosystems or invest in specialized DASH-specific infrastructure.
One of the main challenges facing DASH after its standardization was its own flexibility, expressed through the many features and options allowed by the core specification. Being codec agnostic, for example, is a plus when supporting new codec options, but poses a challenge for encoder or player builders – which codec do you support in your DASH player? What segment encapsulation should the encoder generate? How should DRM be signaled? What closed captioning format do you support? The flexibility inherent in the standard made it more difficult to achieve interoperability between various initial implementations.
Recognizing full interoperability is the key for MPEG-DASH rapid market adoption, the DASH-IF decided to take the raw DASH standard, marry it with a codec, apply tight profiles and other restrictions, and create a baseline recommendation that everyone could use to build interoperable products and services without painful integration. Interoperability is the key to adoption because if a format “works everywhere” then its growth will accelerate. The name of this recommendation is “DASH-AVC/264 Implementation Guidelines” and you can download it from https://dashif.org. It is significant because Microsoft, Adobe, Samsung, Qualcomm, Sony, Akamai, Ericsson and 61 other members of the DASH-IF agreed on a set of recommendations which they will support. They also strive for compatibility with consortia standards, such as HbbTV, DECE, DTG, HD-Forum and DLNA. DASH-IF believes that DASH-AVC/264 supports the Internet streaming main use cases better than any existing proprietary solution. Furthermore, DASH-IF provides conformance software, a set of test vectors, and an open source reference client implementation for DASH-AVC/264. If you are considering a DASH deployment, then a DASH-AVC/264 compatible solution is the best place for you to start. For the technically inclined, here are some of the high level key constraints that DASH-AVC/264 sets in place:
- The required video codecs are AVC/H.264 Main and High profiles. Video tracks using other codecs can be included.
- The required audio codec is HE-ACC v2. Audio tracks using other codecs can be included, including multi-channel audio.
- Segment formats are based on fragmented ISOBMFF (MP4).
- The MPEG-DASH’s “ondemand” and “live” profiles are supported.
- Segments are keyframe-aligned across representations, start with a random access point, and do not vary too dramatically in duration. Therefore, players can switch easily between representations without having to download overlapping segments.
- Common Encryption is used when the content is DRM-protected.
- Closed captioning is supported using TTML-based SMPTE-TT format.
The advantage of an ISO standard is the openness with which it can be evolved and improved by industry consensus. The DASH-IF is the best vector, outside of joining MPEG directly, to propose additional features to the core MPEG-DASH standard. Participation in DASH-IF also provides the opportunity to collaborate with other industry leaders in developing new deployment scenarios and corresponding implementation guidelines for MPEG-DASH. In addition to the work done already around DASH-AVC/264, the DASH-IF has established task forces that are actively addressing other challenging areas of streaming:
Advertising Insertion – the recent DASH extensions provide tools for more efficient server-side ad insertion, and make interoperable client-side ad insertion viable. The DASH-IF Ad Insertion task force is chartered with creating guidelines and interoperability points for both of these architectures. The weekly task force discussions currently revolve around mapping existing workflows into DASH and providing a capabilities gap analysis, with a draft document expected in Q3 2013.
DRM – this task force focuses on interpretation of the DASH and Common Encryption standards to identify and explain best practices and recommendations for signaling and transmitting DRM related information in an interoperable manner. The resulting guidelines, which are included in the DASH-AVC/264document, explain the basic parameters and signaling mechanisms, give on overview of a basic workflow, and show different use models for single keys and key rotation. They also describe simple test scenarios for testing protected content independently of proprietary DRM libraries and servers.
Live Streaming – Further optimization of DASH for live video services, including Linear TV services, is one of the key features of DASH. Due to this workflow, additional aspects in DASH-based live service offerings need to be taken into account to achieve interoperability, best user experience and efficiency. The task force provides guidelines, test cases, test vectors, test service offerings and conformance software to test interoperability for live services. In addition, the task force looks into technical challenges and potential enhancements for improved user experience such as lower latency, improved audiovisual quality and supplemental features such as trick modes.
HEVC – High Efficiency Video Coding is the latest joint ISO MPEG and the ITU-T video codec development with significantly improved compression rates. HEVC was finalized in early 2013 and is expected to provide around 50% bandwidth savings compared to AVC/H.264. Prototypes of HEVC encoding in the combination with MPEG-DASH delivery have shown astonishing quality-differentiating OTT. The HEVC task force addresses interoperability and best practices aspects for HEVC delivered through DASH. The task force collects guidelines, test cases, and test vectors to support interoperability and demonstration efforts. Technical challenges and potential enhancements are discussed and potentially addressed in the relevant SDOs.
Backend Interfaces – deploying, operating and maintaining a backend can be costly, risky and time consuming. Having some well-defined integration points between different providers is a clear help for facilitating such deployment. This group is currently focusing on the interface between an encoder and the DRM platform to facilitate and standardize the exchange of keys and DRM metadata signals. To further increase the value of the DASH delivery ecosystem, this group ensures that encoding protected content against multiple backend DRM platforms is as frictionless as possible.
We strongly believe that there is a common benefit to the entire streaming ecosystem, from studios and operators to vendors to infrastructure providers, in adopting DASH. We also believe that collaboration accelerates adoption. We encourage your organization to use the DASH-IF outputs and join the DASH-IF. Take an active part in defining, tuning, adapting and growing MPEG-DASH and leverage its extended features to enable new applications and business use cases. Make the streaming format of the future today’s format of choice.