CMAF: What It Is and Why It May Change the Future of OTT
The advent of CMAF heralds the beginning of the end for TS containers for OTT delivery, and brings the industry closer to the single format for OTT distributors and playback support on all consumer electronics devices.
Apple’s June 15th announcement at its Worldwide Developers Conference that it will add fragmented MP4 (fMP4) support to HLS marks a significant step in simplifying online video streaming.
Akamai’s Chief (Media) Architect – Will Law, and Akamai Media Product Manager – Shawn Michel, have written an in-depth, and extensive analysis of CSMAF and it’s impacts on the industry (the below is an extract of this analysis).
fMP4 is the parent of the emerging Common Media Application Format (CMAF), and Apple’s plan to support fMP4 brings the industry closer to the single format for OTT distributors and playback support on all consumer electronics devices. The ultimate goal is to reduce the complexity when delivering video online.
The OTT industry has made wholesale shifts over the past five years from using proprietary media protocols such as RTMP, MMS and RTP, towards using HTTP/S to deliver adaptive segmented content to viewers. Within the adaptive segmented formats, there is still significant fragmentation, with HLS, Smooth, HDS and MPEG DASH offering competing solutions. Even with the expected deprecation of Smooth and HDS and their replacement with DASH, most content distributors are still faced with making two silos of content – one in HLS and another in DASH.
Today, HLS specifies the use of TS (transport stream) file containers, while DASH, although allowing TS, almost uniformly uses ISO Base Media File Format (ISOBMFF) in practice, in particular a variant known as the aforementioned fragmented mp4. The result is that content distributors wanting to reach a HLS and DASH audience must encode and store the same audio and video data twice – once wrapped in TS containers and then again wrapped in ISOBMFF. These same files, although representing the same content, cost twice as much to package, twice as much to store on origin and compete with each other on Akamai edge caches for space, thereby reducing the efficiency with which they can be delivered.
To try to overcome the cache efficiency problem, the market has launched a myriad of solutions which require complex synthesis of the TS and ISO segments (for HDS) at the edge or in a streaming mid tier. These servers, which have to build content before they can deliver it, have a lower throughput than those that can simply pass it through. File container diversity therefore limits the total throughput achievable by a delivery server, as well as contributing significantly to our customer’s content preparation, workflow management, and delivery costs. Alternatively, customers could store multiple versions of the content which impact total storage costs.
In mid 2015 two unlikely collaborators – Microsoft and Apple – came together to plan an end to this inefficiency through a new media file format, which at the time was called Common Media File Format but which is now CMAF. Microsoft and Apple reached out to Akamai and a number of their closer partners to iterate on the proposal. In February 2016 this group of companies prepared a joint submission to MPEG, which has been accepted onto a standardization track.
CMAF is very similar to the file container that DASH already uses today, so adopting CMAF from the DASH perspective requires little, if any, change to encoders, workflow or players. For the Apple and HLS community however, it requires parsing a new type of container. Apple’s announcement to support fMP4 in HLS under iOS10, macOS and tvOS gives the industry more confidence that CMAF will live up to its billing as the driver of convergence.
The advent of CMAF heralds the beginning of the end for TS containers for OTT delivery. The benefits of encoding once, packaging once, caching once and building a single type of player are too attractive along the delivery chain for TS to persist in the long term.
It is not all ice-cream cake however. Even though Apple, Android and Microsoft operating systems and devices will quickly support CMAF, there will still be many legacy devices that are non field-upgradeable for which TS-based HLS will continue to be needed.
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