One of the worst nightmares a filmmaker can suffer is the long and painful process of designing an HD production. When you go outside to check what options you have available, you'll find that the market wants to force you to make decisions about things you've always taken for granted: do you want progressive or interlaced video? What will be the final distribution format? Want 64:1 compression? Where is the money going to come from to pay for those $250 cassettes? Is it necessary to look for special lenses? What options are there for post-production?... and to complicate matters, not always the best camera, the best optics and the best recording system are under the same roof.
What to do in the face of this mess? Perhaps the first thing is to accept that, after all, it does not constitute a disorder. It is true that in the Betacam era things were easier, but if the industry offers options in terms of resolution, frame cadence and compression, it is because the market has many faces: it is not the same to produce in HD to distribute in 35 mm, to broadcast live sporting events, to make corporate video or to set up a soap opera factory.
One more format, some less problems
Sony may be able to bring some stability to the confusing world of high definition. At NAB 2004, a new HD recording format, HDCAM SR, was presented in partnership. As often happens in these cases, the format had been announced since 2003, and even before becoming a real product it already generated favorable reactions in the industry. Discreet and Quantel announced that they will support operations based on HDCAM SR. CBS and Fox accept footage recorded in HDCAM SR. The main rental houses in the North American market already offer HDCAM SR equipment. And the final boost comes from the meritorious George Lucas, who is using HDCAM SR to conclude the "Star Wars" saga.
The most important thing for the confused Latin producer is that everything seems to indicate that HDCAM SR is going to become the heir of Digital Betacam as a universally accepted distribution format. In plain language, this means that we already know in what format we will have to master... and reaching some degree of standardization on that front represents a breakthrough because it has the potential to simplify costly decisions related to post-production processes.
SR: many bits
What's so special about HDCAM SR? The SR suffix comes from Superior Resolution. Like most equipment to produce in HD, each HDCAM SR device has somewhere a switch that allows the user to choose between several signal recording schemes depending on cadence and number of pixels per frame. By moving this switch we are making decisions regarding definition. But HDCAM SR offers clear advantages in resolution, an image quality that generally must undergo subjective evaluations. The superior resolution of the new format essentially comes from the increase in bandwidth and improvements in its compression system, factors that allow images recorded in HDCAM SR to be visibly better than those offered by other formats.
Under normal conditions, an HDCAM SR recorder uses half-inch tapes to handle streams up to 593 Mbps, of which 440 Mbps are applied to the recording of compressed video using MPEG-4-based procedures. A conventional HDCAM transport handles up to 270 Mbps, of which 143 Mbps correspond to compressed video through procedures that Sony has never disclosed but that are apparently similar to those used in Digital Betacam recorders; some specialists assume that these are variations on traditional M-JPEG schemes, possibly similar to MPEG-2 systems that only use intraframe compression.
Moreover, the HDCAM format does some tricks before compressing the image. First, the effective image resolution of 1920 x 1080 pixels is reduced to 1440 x 1080. And to compress it, a quantization matrix is applied that provides results equivalent to a 3:1:1 sampling. This sounds terrible, but remember that one of Sony's goals when it designed this format was to make it viable to handle HD signals using the same bandwidth of uncompressed SD signals. And to be able to package an HD signal in a 270 Mbps stream, it is necessary to make some commitments.
HDCAM SR doesn't do tricks before you start compressing. Taking as a reference a 1080i signal, each frame is recorded with the full resolution of 1920 x 1080 pixels. In addition, users have the option to preserve the 4:4:4 sampling of the HD-SDI signal originated by the best quality cameras.
Let's clarify this. HDCAM SR can handle HD signals encoded in the usual way, such as 10-bit component video with 4:2:2 sampling, but also has the ability to record RGB signals with 4:4:4 sampling - this means that HDCAM SR allows to eliminate the bandwidth reduction of color information, procedure inherited from PAL and NTSC television systems. Breaking the barrier of the COLOR subcarrier HDCAM SR makes gamut problems and color space inconsistencies that mercilessly complicated the lives of colorists, graphic artists and tape-to-film transfer system operators a thing of the past.
Compress less, compress better
HDCAM SR compresses the video using MPEG-4 Studio Profile, a system specially designed for HD images and which is much more efficient than MPEG-2. The video recorded in HDCAM SR reaches a compression rate of 2.5:1, which is quite "smooth" in terms of temporary compression. As a point of reference, let's remember that the video streams delivered by satellite television systems apply MPEG compression with rates that can be higher than 100:1 - and even so, they deliver images that are acceptable to a large part of the viewing public.
It is materially impossible to make mathematical comparisons between the compression scheme of the HDCAM SR format and those applied by other formats, but what we can categorically affirm is that HDCAM SR resists any subjective test and for practical purposes we can think of using it as a format without loss of quality by compression, such as the Digital Betacam. This explains its rapid acceptance by the most important organizations in the industry and makes it seem like the ideal distribution format for the coming years.
Let's pause at this point. Attention: does all the above mean that both Sony and the other manufacturers of HD recording systems have been deceiving us by offering us lower quality formats? No way! Sony HDCAM, DVCPro HD and Panasonic D5-HD are formats tailored to the bandwidth availability of their time. Recording 270 Mps on a half-inch tape or packaging an HD signal in 100 Mbps are still important achievements based on the state of the industry in the mid-nineties. What happens, simply, is that now we can do things even better.
These formats will remain in force in production and post-production environments, because despite offering compression rates of 10:1, or even higher, they continue to deliver images of excellent quality. When CineAlta came out, Sony said that good quality recordings on HDCAM media were comparable to a 35mm distribution copy. Maybe that statement forced things a little bit, but it's very close to the truth as to the viewer's experience. And let's not forget that HD cameras have improved dramatically in the last five years...
Some extra things...
The HDCAM SR equipment offer includes some surprises. The first is that the format handles 12 channels of digital audio 24/48 in PCM format, without compression, which allows us to think of applications such as distribution of two 5.1 audio mixes in a single cassette, something that is not bad if we remember that it is half-inch tape. The recorders come ready to record metadata on digital audio channels.
The axis of the family is the HDC-F950 camera, a modular system that can be adapted for studio, EFP or digital cinematography applications. As expected, for now it is not possible to configure the F950 as a camcorder. For field use it is necessary to resort to the SRW-1, a portable recorder that can record 4:4:4 or 4:2:2 signals interchangeably. The main attraction of the SRW-1 is that it can simultaneously record two HD signals with 4:2:2 sampling, making it the ideal support for stereoscopic video applications, for recording isolated cameras at special events or for whatever you can think of. Under these conditions, the recorder registers just over 900 Mbps!
Sony's offer is complemented by the SRW-5000 studio recorder, a publishing machine specially designed to avoid tape interchangeability problems. This recorder can be equipped with a complete repertoire of converters that facilitate its integration into existing installations. As usual at Sony, compatibility with the above formats is offered: the SRW-5000 can play conventional HDCAM recordings.
However, it should be noted that for now it cannot play the dual recordings of the SRW-1, although it is conceivable that in the near future Sony will offer full compatibility in its offer of HDCAM SR recorders.
The emergence of HDCAM SR is producing some interesting moves in the industry. CineAlta with SR quality is very attractive for the world of digital cinematography. HDCAM SR is a viable support for handling high-quality HD signals on tape, and that makes the format an excellent medium of exchange for the great diversity of HD platforms that the industry offers. This explains its rapid acceptance at the high level of the industry, despite its cost, which for now is significantly high. And finally, HDCAM SR reduces a little the confusion of the world of HD production, but it does not prevent us from continuing to study at a forced pace to be able to make the right decisions the moment we make our entrance to the attractive world of high definition.
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