In a race to the finishing line, Sony’s XDCAM HD422 triumphed over major competing brands to become the camcorder of choice for leading Taiwan broadcaster Eastern Broadcast Company (EBC) transmitting on air as Channel ETTV.
According to ETTV VP of Engineering, Chou Long-Huei, the XDCAM’s superior HD video quality, HD storage efficiency, and proxy workflow advantages were the key clinchers for the purchase of 20 units of the XDCAM that will be deployed in the news and programming departments.
ETTV has actively pursued a digitalisation process over the past six years with serious investments into tapeless production workflow, digital servers and NLE editing consecutively.
He added, “ETTV started its camcorder acquisition evaluation in the second half of 2009, analysing seriously the XDCAM’s advantages with regard to connection of digital workflow from acquisition to archive. We had to ensure that our future camcorders integrate seamlessly into the station’s current system and workflow.”
Chou said ETTV’s engineers were pleased to learn that Sony’s Mpeg GOP 50M bitrates provided the key to reduce server storage capacity and release the burden of bandwidth and the PDW-700 picture quality good.
Taking into account the reliability of Sony’s products and the good after sales service provided, the station decided to go with Sony’s XDCAM.
Another fact that was taken into consideration was that Sony’s interface is similar for end users between SX and XDCAM and this was good as it reduced adoption time in the learning curve.
The challenge to deliver HD video quality
Chou said, “The key challenge for us down the road is the increasing use of HD video quality demanded by viewers. A camcorder that can deliver this without us spending more to increase storage capacity is very important. The cost of storage expansion is very expensive.”
Available HD codec uses 100Mbps or more bitrate for the equivalent picture quality. XDCAM HD422 uses 50Mbps which is half the bitrate and therefore uses only half of the server storage (given the equivalent picture quality).
The XDCAM’s Proxy workflow capability was also an added advantage for ETTV’s news crews who sometimes have to relay material back from remote locations. Proxy is a smaller version of the original high-resolution footage. It is around 2Mbps and 25 times smaller than its original size with an equivalent to VCD quality. It is easily transported or transferred over the network. This is especially useful in ETTV’s application such as “breaking news” where the TV station can receive footages to go “on-air” from out-station locations through network transfer without requiring the journalist to return to base station.
In yet another example of proxy application, the ETTV producer can be away from the production location but he or she is able to view the production if the proxy can be delivered to the producer through the network. ETTV found that the Sony XDCAM afforded them this luxury.
Compatibility with AVID editing system
In terms of compatibility, ETTV discovered during the evaluation period that Sony’s format or codec worked well with the ETTV AVID system. This is because of the complexity needed to compute the new AVC entropy coding techniques of CABAC and CAVLC at HD resolutions. Currently, software based encoding or decoding of AVC codec is still not efficient for broadcast applications.
The advantages in compression efficiencies offered by AVC codec are almost entirely based on its better exploitation of compressing a group of frames (rather than single frame or intra-frame). Hence, compressing HD images with the use of intra-frame techniques, the AVC algorithm is forced to operate at high compression factors resulting in lower picture quality for broadcast applications. These high compression ratios not only produce unacceptable results (even on a single pass), especially with complex pictures, it can also render the “acceptable” pictures very “weak” for multi-generation work.
It has been said that “AVC is more efficient than MPEG-2 Long GOP” This statement would be accurate when comparing an “AVC Long GOP” scheme (with all of its compression techniques at their fullest performance) against its equivalent implemented with MPEG-2 Long GOP. However, an AVC based intra-picture compression discards most of its advanced techniques resulting in an intra-picture scheme with just 15-20% more efficiency as compared to other intra-only techniques (e.g., DV, JPEG, MPEG-2 Intra, etc).
Therefore, the long GOP techniques of MPEG-2 create significantly better picture quality than an AVC based intra-picture compression scheme of similar data rate. Or, viewed from a different perspective, MPEG-2 Long GOP produces approximately from 1/3 to 1/2 the data rate required by an AVC based intra-picture scheme at similar levels of picture quality.
Even with the use of only single frame compression, AVC is still very complex to compute due to ‘Intra-Picture” prediction modes, and mostly by newer mathematical techniques for entropy encoding (such as CABAC and CAVLC). Based on Sony’s preliminary tests, more than 150 Mbps would be necessary to produce acceptable levels of picture quality for multi-generation work on HD signals.
At these high bit-rates and with the possibility of software solutions for real time encoding/decoding (at the present time), the possible benefits of the new algorithm are negated when compared to existing intra-frame techniques and to the MPEG2 Long GOP system.
With the existing generation of Dual - and Quad-Core CPUs, it is now possible to encode/decode multiple streams of HD MPEG-2 Long GOP signals and real time with software-only tools.
ETTV says the Proxy workflow advantage is contributing substantially to efficiencies in production and Sony XDCAM’s reusable discs is reducing media costs for production dramatically. Commenting on a key feature that is bringing benefit to the station, Mr. Chou said,” the clip-continuous recording” function really reduces the number of clips and thus results in reducing ingesting time. Another point worth mentioning is “Cache recording” which makes it convenient to shoot without missing any important moments.”