is the heart
and soul of the
media facility—think Serial Digital Interface,
AES3 for audio,
HDMI and other transports
that move audio and video from
point to point in a timed,
As previously mentioned in this column,
IT methods and especially Ethernet are destined
to replace/augment SDI over time.
There is much industry activity to create
the best practices and standards that will
enable interoperable AV connectivity using
Ethernet/IP. The new methods will be
cloud-friendly in ways that SDI could never
We’ve all gone shopping to replace
some worn-out item. One choice is to find
a replacement that is nearly a clone of the
original. Or, enticed by the new, we look for
an item with the latest bells and whistles.
We are now standing at the door of opportunity
for creating an “Ethernet/IP AV transport”
ecosystem. Should it be plain vanilla
or a souped-up version?
The new networked transport version
has many novel features lacking in SDI (and
AES3 audio). See Fig. 1; is this the perfect
set of characteristics? Should they be different?
Let’s not debate it here. From my
involvement in industry forums (especially
the Joint Task Force on Networked Media)
this set covers the main enhancements that
many want to see. There is no room here
to describe each new element in detail. So
the approach is to review them now and
expand in future columns.
THE NEW STREAMING,
PIECE BY PIECE
At 12 o’clock in the figure, see “New
stacks.” This relates to the layer 2 (MAC)
and layer 3 (IP) data layering over Ethernet
transport. One requirement is to layer
SDI payload data over RTP/UDP/IP. This has
been done using SMPTE standard St2022-6.
|Fig 1. A future view of professional networked streaming
Here, each payload unit is time-stamped
and filled with 1,376 bytes of image data.
St2022-6 was implemented in several NAB
Show product demos as a replacement for
SDI. That said, the industry may need to
tweak the specs slightly so it fits into a bigger,
flow-harmonious framework. The flows
may include video, audio, intercom, control,
metadata, AV proxies and others, so, the total
IP payload will be more than St2022-6
supports today. Also, the IEEE work on AVB
is an alternate way to view the stack and
other important QoS aspects.
Now see “Compressed essence” at 2
o’clock. SDI is uncompressed today. When
a facility needs to stream UHD/4K images,
applying a light compression will ease transport
specs. For example, 4:2:2, 10 bit UHD
requires a future 12 Gbps SDI link or a 40G
Ethernet link. By applying 6:1 visually loss-less,
low-latency compression the flow may
leverage 3G SDI transport or 10G Ethernet.
Several NAB Show vendors showed compressed
video over IP. Note that Ethernet is
bidirectional whereas SDI is unidirectional.
Also, more than one video payload can be
packed into Ethernet up to rate limits. So, it
seems reasonable that the new data formats
should permit compressed streams, but not
demand it. Selecting interoperable compression
format(s) is a future effort.
At 3 o’clock is “Interop/bridging.” This
relates to creating a future networked ecosystem
friendly to the SDI world. This requires
carrying SDI payload as one option
using Ethernet/IP. When spanning domains,
dropping data elements or transcoding AV
formats looks like a “bridge over troubled
waters.” So, efforts will made to align data
types for smooth conversions between SDI
and Ethernet/IP flows.
From 3:30 to about 7 o’clock in the figure
are four related aspects (Range to New
Physical layers). This is a list of networked
features not available with SDI. Range-wise,
IP flows can be device-to-device in the same
room or across the world. Of course, long
distance transport will seize tolls due to
more loss, more latency and reduced rates.
These negatives can be managed and still
achieve acceptable performance. In 2014,
100 Gbps Ethernet is a reality and can transport
4:4:4, 12-bit, UHD2/8K flows at 96
Gbps (assumes Ethernet jumbo frames).
Finally, there is a wide range of standardized
Ethernet physical link types to
choose from including Cat 6a copper with
RJ45 connectors for 10 G (to about 100m,
same as SDI over coax), multimode fiber
(to about 300 m) and single mode fiber (to
about 80 Km).
At 8 o’clock is “Push/pull” support. What
does this mean? SDI streams are pushed
to a receiver from a sender. The receiver
needs to drink the continuous data stream;
there is no stopping it. On the other hand
HTTP (uses TCP for reliability) is a pulled
transport. So, imagine a client pulling video
one frame at a time from a server.
The average performance looks like a
streamed flow even if the flow is delivered in
uneven chunks; receiver-buffering smoothes
out any irregularities. Note that the latency
per node could be a full frame of video. Pull
has a pro/con list just as push does. It is likely
that pull will find a home in the new world
and especially in the public cloud. Pulled
point-to-multipoint is problematic for a number
of reasons not discussed here.
Last is the 9 o’clock item “Stream splicing.”
There is no getting around it; it’s
easy to frame-accurately splice two (A, B)
video streams in an SDI router compared
to using Ethernet/IP switching. That said,
there are numerous ways to do this and
several NAB Show vendors demonstrated
frame-accurate video/IP stream splicing.
Problem solved. However, our industry
still needs to select a preferred method
Bottom line, the new streaming world is
upon us. Stay tuned in for exciting advances
over the next year and be sure to ask for
demos at the 2015 NAB Show.
Al Kovalick is the founder of Media Systems
consulting in Silicon Valley. He is the
author of “Video Systems in an IT Environment
(2nd ed).” He is a frequent speaker at
industry events and a SMPTE Fellow. For
a complete bio and contact information,