Video-Over-IP: AIMS, ASPEN Compared

LOS ANGELES- Happy New Year 2016! Well, I had thought to start the new year with a fresh topic, maybe something non-controversial such as high dynamic range or 8KTV. But as 2015 was wrapping up, new developments in IP transport of live uncompressed (or mezzanine compressed) video have compelled me to continue on with this theme of video-over-IP.

In my last few musings, I compared the real-time transport of video streams using IP standards, such as SMPTE 2022, versus the conventional use of serial digital interface over coax. In conclusion, while SDI is still relevant and has recently been upgraded to 12 Gbps rates, IP transport of video is an upcoming method proposed by many of the major equipment vendors. (See 12 Gb SDI Cost, Cables and Capabilities, Dec. 9, 2015.)

In late 2015, there were announcements from two organizations promoting video-over-IP. One is called AIMS (Alliance for IP Media Solutions) and the other is called ASPEN (Adaptive Sample Picture Encapsulation). AIMS is supported by Imagine Communications, Grass Valley (Belden), Cisco, Arista Networks, Snell Advanced Media, EVS Broadcast among others. ASPEN is led by Evertz with support from For-A, Ross, Abekas, AJA Video Systems, ChryonHego, Hitachi, Sony, Tektronix, VizRT among others.

While both organizations support the idea that the future of video transport will use IP like protocols for switching and delivery, they differ in how they manage the important requirement of video synchronization. AIMS builds on SMPTE 2022 (which, if you recall, came from the Video Services Forum) as a method to use standard IP packet distribution for live video. The core timing is derived from the use of IEEE 1588 Precision Time Protocol to generate RTP with RTMP time stamps. While SMPTE 2022-6 specifies the packetization of the whole SDI signal into packets, there are ongoing efforts in SMPTE to standardize the individual packetization of video, audio and associated data (VSF has standardized this approach in TR-04).

ASPEN builds on a proprietary method developed by Evertz, based on MPEG-2 Systems transport over IP. Currently documented via RDD 37 (Registered Disclosure Document) as well as SMPTE ST 302 and 2038. MPEG 2 Systems (ISO 13818-1) synchronizes video and audio streams via an embedded system clock (27 MHz) using a 90 kHz counter as part of an adaptation header.

Both proposed standards also include mezzanine compression to reduce internal bandwidth. AIMS uses TICO, a wavelet-based intraframe compression method (undergoing SMPTE standardization). ASPEN uses JPEG 2000, an ISO standard (15444-1). JPEG 2000 has a range of compression ratios from mathematically lossless 2:1, to a more aggressive visually lossless compression of 4:1 or higher.

What are the important considerations? First, SDI is still a valid approach, one which is standardized, well understood and is routinely used for video production. The second consideration is that each of the video-over-IP approaches uses different methods to encapsulate video, audio and data and to provide proper synchronization. Finally, video-over-IP methods have been demonstrated as workable and have been adopted by several notable video production facilities.

Will these two approaches be interoperable? Lets hope so, if only via the brute force method of converting to SDI and then re-packetizing. Clever solutions should evolve that can enable the interchange between AIMS and ASPEN encapsulated video and audio signals.

There is also uncertainty regarding the use of commercial off-the-shelf IP switches for transport of live video and audio signals. Which IP switches will support which protocol? And there are other considerations regarding IP distribution of video and audio streams such as routing optimization algorithms, directory services (what's in which packet) and latency/bandwidth management.

So our wish for 2016? Let's hope that all the promises of AIMS and ASPEN come to fruition.

(Corridendum: Steve Reynolds, chief technology officer of Imagine Communications, has pointed out that AIMS is focused on un-compressed video and audio transport and routing and while they have may eventually support compressed video on their roadmap, they have not selected TICO or any other mezzanine video compression method. Further the transport of audio is standardized using AES 67 with the use of SMPTE 2059 (IEEE 1588 PTP) as the common synchronization method. The primary documentation for AIMS encapsulation methodology is found in VSF TR-03 (component RFC 4175) and TR-04 (SMPTE 2022-6). Jim D.)

Jim DeFilippis is CEO of TMS Consulting, Inc., in Los Angeles. See more of his contributions in the Author's Archive.

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