The arrival of single-slice HEVC encoding for live contribution is a significant milestone in the roll-out of UHD services, with Ericsson and BT Media and Broadcast (BT M&B) demonstrating the technique for the first time in September. BT Sport was showing live AVIVA Premiership rugby matches in UHD to IBC visitors, with the signals routed via Ericsson’s Playout Centre in Hilversum, Netherlands, and onto the Ericsson and BT M&B stands.
Whereas in the past, UHD contribution feeds have been made up of four separate streams (quadrants) that are then stitched back together – each one encoded using the AVC/H.264 codec – BT Sport can now encode live action using HEVC instead of AVC and using a single encoder instead of four. A migration from AVC quadrants to HEVC full-frames also means the whole delivery chain, from outside broadcast trucks to television screens, can now be converted to HEVC where appropriate.
Dr Giles Wilson, CTO and Head of Portfolio & Architecture for TV & Media at Ericsson, points out that HEVC encoding is already established for distribution (from playout locations to homes) but contribution represents a much bigger challenge. Contribution requires higher picture quality (as this is source content, which also means it has to be 4:2:2 chroma sampled rather than 4:2:0 to enable mixing, like for graphics), with higher bit rates and low latency. This means greater demands on video processing.
“When you move to something that is very processor intensive you can make the challenge easier by dividing the picture and splitting the processing across four encoders that create four combined tiles. The down-side for this approach is that you lose efficiency,” he explains. “We can do some clever things with tiles [to get the best outcome possible] but this approach does not allow motion vectors to be projected from another tile and it limits how hard you can push the encoding because you cannot rate control and balance across the edges, as you do not want the edges [between the four tiles] to be visible.”
Ericsson has new encoding/decoding technology that makes it possible to use HEVC and use it on a single encoder to perform one encode for the entire UHD/4K picture. There is no need for complex AVC quadrant generation. Notably, when you use a single encoder you only need a single receiver, too. Ericsson says the new approach delivers a 40% bandwidth saving on the previous technique (partly because you now get to use HEVC rather than its predecessor, AVC). Wilson says broadcasters will want to move to single-slice encoding as soon as they can.
“This is a turning point in UHDTV,” declares Elisabetta Romano, Vice President and Head of TV and Media at Ericsson. “It makes 4K live sports and events a practical, cost-effective and high-quality reality for the first time. We can drive better quality, operational simplicity and bandwidth efficiency.” Mark Wilson-Dunn, Vice President at BT Media and Broadcast, says, “The combination of the new equipment with our new UHD links truck will deliver unbeatable high-quality sports footage to viewers.”
BT Sport UHD was the first ultra-high-definition channel to launch in the UK and is one of three BT channels that Ericsson was contracted last year to help launch and run (the others being BT Sport Europe and the free-to-air service BT Sport Showcase). In 2013, Ericsson and BT produced the world’s first multi-camera production of a live sporting event in a 4:2:2, 10-bit resolution 4K UHD signal at 60 frames per second using AVC compression.
Photo: AVIVA Premiership rugby on BT Sport (courtesy of BT)