WHICH 'PEG FOR POST?
As the world turns to HD, there is an increased focus on quality throughout the production chain. New technologies enable new, distributed workflows. The TV and film industry is looking for remote editing, often in a different time zone, so that they can move towards cost-effective 24-hour operation. This means that very high quality video needs to be transported thousands of miles without any loss in quality. The TV industry has been transporting MPEG-2 4:2:2 over Ethernet connections successfully for a number of years, but as bandwidth becomes affordable and high definition enters the scene, the advent of the higher video quality JPEG2000 — the digital cinema standard codec — is beginning to give MPEG-2 and MPEG-4 a run for their money.
THE RISE OF IP
The video world is moving to IP because of greater efficiencies and the lowering costs of fibre. Research indicates that presently 60 percent of video contribution network investments are for IP-based solutions and this move towards is IP is accelerating.
By taking advantage of the inherent flexibility of IP, broadcasters and movie producers are provided with efficient, cost-effective and scalable solutions for professional quality video transport. In addition to IP networks being much more cost-effective than legacy distribution, IP also enables significant set-up and running cost savings.
Historically there have been concerns regarding the inherent Quality of Service of IP networks and the ability to carry time critical IP packets such as those building up a video stream. These concerns are being addressed by deploying managed networks combined with video gateways supporting Forward Error Correction (FEC) for the recreation of lost packages and advanced buffer management for removal of network jitter.
It is clear that just like most other industries, IP is increasingly moving towards a dominant position for the delivery of TV and film content. By choosing IP-based solutions, the likely life of the infrastructure is increasing and making it easier to enable new functionality through integrating solutions not yet on the market, to provide functionality not yet anticipated.
THE DIFFERENCES BETWEEN MPEG AND JPEG2000
When coding a video sequence for a modern transmission or storage system, the first question is what is the desired bit rate?
With MPEG compression, the raw frames are compressed as one of three types of frame: intra-coded frames (I-frame), predictive-coded frames (P-frames), and bi-directionally predictive coded frames (B-frames). The combination of these frames is then arranged together in a Group of Pictures structure (GOP). Because the bits per frame need to be allocated based on the GOP and because some coding is based on future frames (B-frames are bi-directional), MPEG introduces considerable latency, a major issue for live event video.
JPEG2000 is a wavelet based compression technology, which provides a number of benefits for production over Discrete Cosine Transform (DCT) compression methods such as MPEG-2. JPEG2000 is an intra-frame based encoding scheme. Unlike DCT-based compression methods, which encode using I, P or B –frames, a JPEG2000 encodes each frame independently. This is a great advantage for editing, as the video may be cut and edited in any wanted place as there is no need to consider the GOP structure of MPEG.
An important JPEG2000 differentiator is that it offers a tool set suitable for high-quality video. Whereas the driving force for MPEG-2 and MPEG-4 has been to deliver a good video quality at low bit-rates (e.g. for TV over satellite or DSL lines), the driving force behind JPEG2000 has been to produce a standard with high quality compression of single pictures. This requirement fits well with really high video quality applications such as post production, Digital Cinema and broadcast contribution.
JPEG has advantages in video quality. MPEG-2 and MPEG-4 are limited to 8-bit video and the 4:2:2 profile, however JPEG2000 can allocate more bits per sample (e.g. 10 bit video and 4:4.4 structure with 12 bit video are both supported), in line with normal studio practice.
Unlike MPEG, JPEG2000 also provides a lossless mode in addition to the lossy mode. This means that for applications where no degradation is accepted, the video can be compressed by more than 50 percent without compromising on quality. Additionally, in MPEG the picture is divided into blocks and the DCT operation is performed on the blocks, creating artifacts on the edges of the blocks.
One of the challenges of MPEG-2 compression is the quality degradation at every compression step. JPEG2000 compression technology is not similarly affected, sustaining multiple compression steps without a drop in video quality. Achieving low latency is crucial for live production and also for remote editing.
Several alternatives exist for encapsulation of JPEG2000 data into IP datagrams. Based on the requirement for a simultaneous feed of both decoder and video servers, the MXF format is an ideal choice for encapsulating the video, audio and ancillary data for streaming. The advantages of this encapsulation compared to an MPEG2 transport stream encapsulation are that this method provides perfect lip sync, supports the compressed bit rates from SD to 3Gb HD, and allows for frame aligned FEC with no added latency.
SO, WHICH 'PEG FOR POST?
MPEG is going to be around for decades. A major area where it will continue to dominate is as final distribution format over relatively low bandwidth networks, such as IPTV and Pay-TV. Here, MPEG-2 and -4 have major advantages over all other formats. However, for the distribution of video, particularly where high quality and latency matter, JPEG2000 is catching up fast and has some very real advantages. It is already the preferred format for digital cinema and we have pioneered its use in the broadcast market, particularly for the contribution of live events such as sports.
For the post industry, JPEG2000 has a lot to offer. Our JPEG2000 video gateways are already facilitating the West Coast editing of a major US TV dramas. In this case the video is stored on servers in New York and accessed by post production staff on the West Coast. Our JPEG2000-based solutions enable a longer working day — important when deadlines are tight — and also mean that a studio can make the most of editing talent, wherever it happens to be based.
Our belief is that the post industry will increasingly find that clients want to make use of JPEG2000 for transport video. The advantages in quality and latency are just too difficult to ignore and if you’re working in the digital cinema market, using JPEG2000 as early as possible in the workflow has many advantages. You can’t ignore MPEG just yet, but it’s increasingly likely that JPEG2000 will become an important part of your day-to-day operations.
Oslo, Norway's T-VIPS AS (www.t-vips.com) is a fast-growing technology company specializing in providing Intelligent Video Transport Solutions of live broadcast signals. T-VIPS products are designed and used for applications such as broadcast contribution, studio-to-studio media exchange, primary distribution from TV play-out to transmitter, in-house signal distribution and routing, post-production, sports and other live event coverage, regional adaptation of transport streams, DTT adaptation systems and general video transport. They have US offices in Millburn, New Jersey.