Smoothing Out The Video Stream

In its latest effort to help smooth out cable’s videostreaming ecosystem for Internet-protocol video and TV Everywhere apps, CableLabs has pumped out a new set of specs that aim to bring unity to a mishmash of methods that have traditionally been used to prepare streams for delivery to tablets, gaming consoles and other connected devices.

The new OpenCable “Adaptive Transport Stream” specs, quietly issued last month, should also get cable operators a step closer to a technically uniform cloud-based streaming platform that can be supported by a large group of video encoding and packaging vendors.

Historically, the video encoder and the video packager (the piece that puts the video into the right adaptive-bit-rate format, such as MPEG-DASH, Apple HTTP Live Streaming or Microsoft Smooth Streaming) were crammed into the same box. The CableLabs specs will provide a new means to separate those functions and establish an interoperability link between them.

In addition to enabling each side of that equation to scale independently, the specs should also help MSOs choose from different encoding and packaging vendors. If those suppliers adhere to the specs, they should work together without more heavy-handed integration efforts.

Adaptive bit-rate (ABR) streaming “is a reality now,” Yuval Fisher, chief technology officer of video encoding and packaging supplier RGB Networks, said, noting that it’s widely used by everyone from Netflix to the MSOs that offer TV Everywhere apps on tablets and other IPconnected devices. “But some of the infrastructure is not that well-defined. It’s been a bit of a hodgepodge.”

That hodgepodge includes how video that originates from the service provider is morphed into one of the various ABR formats before it can be shuttled along to the user. While Apple, as one example, addresses some of that in its specs, there are bits missing to complete the picture.

MSOs, meanwhile, have tried to fill those gaps through their own interoperability tests or by dictating that their vendors work together. “This cleans up and solidifies some of the steps,” Fisher said.

The new specs do not cover how video should be encoded. CableLabs solved that last fall with the release of a separate but related spec that unifies how the primary master-like “mezzanine” file of a video title is encoded before it is converted into ABR streams for delivery to the end device. The new specs also define so-called “fragment boundaries” that aim to keep the video running smooth even as bandwidth conditions change.

In the ABR process, video streams are chopped into small chunks of video at different bit rates and resolutions that are each a few seconds long. With a goal of eliminating buffering, the ABR stream boosts or decreases resolution based on the available bandwidth. But each of those segments must be stitched together smoothly so the continuity of the video isn’t affected, even as the resolution and bit rate jump up or down.

The use of common, pre-defined fragment boundary points should ensure that the ABR video segments are spliced together properly without having to resort to vendor-specific, proprietary implementations.

“There were four to five different ways of doing it. Every vendor had its own way,” Fisher said.

Those fragment boundaries will help to clarify how dynamic ad insertion is implemented in ABR streams, as they ensure that the ad and the programming are lined up properly. The specs should also broaden the vendor playing field of encoding and packaging vendors that includes Arris, Cisco Systems, Ericsson, Envivio, Harmonic, Elemental Technologies, and RGB Networks, among many others.

Products based on the new Adaptive Transport Stream specs will only need to pass an interoperability test showing that they can work with other equipment. CableLabs expects to start ATS interop testing later this year, Mukta Kar, CableLabs’ lead architect, said.


CableLabs’ Adaptive Transport Stream spec will move MSOs a step closer to a technically uniform, multivendor platform for cloud-based video streaming.