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Going Tape-Less: Inside the codecs and formats of tape-less acquisition

In this first of a three-part series Mike Jones takes a look at the XDCAM HD format and its latest addition XDCAMHD EX By Mike Jones

Never has the digital production landscape been so diverse. Depending on your perspective you'll either see this as a time of unprecedented choice or unprecedented confusion; for most it will be equal measures of both. As if the move away from standard definition weren't enough on its own we now face a quiver of HD acquisition format variants and combinations for professional production. And beyond just HD itself what has certainly been capturing the attention of digital producers across all genres and forms is the long awaited move to a tape-less workflow.

But where to begin? Flash memory, hard drive or optical disc? Long GOP, wavelet or intra-frame codecs? The answer is of course never straight forward, any choice of format is invariably (or at least should be) a weighing up of Pros and Cons in concert with the particular needs and nature of the production being served. There is no ?Best format, only the ?Best format for the production youre making and the way you like to work. In this light we present a detailing of some of the key pros and cons of the popular and on-the-horizon tape-less formats to make your next choice a more informed one.

In order to be specific in comparing these formats I should point out that we deliberately focused on the acquisition format and codec and not the respective cameras that acquire in these formats. These can vary enormously in cost by tens of thousands of dollars, not to mention physical size, from hand-held to shoulder-mount, so it would not be a useful set of comparisons. Instead we look at the attributes of the format itself, its capture, transfer, quality, assembly and production efficiency.


What should also be noted before waddling on further into the HD mire below is that some of the formats discussed here are still waiting to be seen in the flesh. Those that are new have been officially announced but are in some cases not yet shipping with plans for them to be hitting the streets over the coming year. What you'll find below is an overview of what's available and what's just around the corner.

XDCamHD / Optical Disc
One of the older and better established tape-less systems available, Sony's XDCamHD is the High Definition evolution of XDCam and has seen strong take up in ENG broadcast situations as well as documentary and TV drama production.

Pros

  • XDCAM discs are a physically robust format with almost no chance of being scratched or marred. Drops, shocks and bumps won't worry it. Rolling over it with the car however is probably not a good idea
  • XDCAM discs make for an excellent shelfable source master/archive format and when kept in a cool, humidity-free room will maintain integrity over long periods of time
  • XDCAM discs are very cheap at less than $50 a disc with 23GB of data storage
  • Long record times of up to 100 minutes of highest quality 35mbps bitrate
  • Simultaneous low-res proxy file recording for preview and proxy editing on low-power computer systems
  • Very efficient and manageable file sizes
  • Embedded essence markers for media management and metadata in the MXF format
  • The XDCAM disc serves as an holistic archive format with the ability to save non video data (such as EDLs, photos, scripts etc) to the disc along with the video itself.

Cons

  • Potential issues with the long GOP compression structure
  • 8-bit color space

The hard media format for XDCamHD is an optical disc (called a XDCAM professional Disc) built on Blu-Ray technology and mounted in a casing not unlike a large minidisc. This casing offers significant data protection and physical robustness and indeed there are stories of XDCam discs dropped into swimming pools, lakes and ocean seas only to be fished out, dried off and put back to use.

XDCAM Professional Disc

Sony has continued to develop and expand XDCam over the years since its release some four years ago showing it is taking a long term approach to the format and indeed that the initial spec was open and flexible enough to accommodate ongoing evolution. This is an admirable quality in an age of disposable obsolescence.

XDCAM HD records in MPEG-2 codec at selectable bitrates of 18, 25 and 35mbps. At NAB07 Sony announced next generation XDCAM HD hardware that will boost this to 50mbps and also increase the color sampling from 4:2:0 to 4:2:2. Currently a single XDCAM Professional Disc can record up to 60 minutes of 1080i at 35mbps but new double layer discs have been announced that will boost record times to 100mins at 35mbps. Any way you slice it this is a respectable signal in long record times with all the benefits of tape-less, non-linear acquisition.

XDCamHD is arguably one of the most flexible and efficient HD formats available. However, many of the key strengths of XDCamHD come beyond the image itself. Proxy recording provides a simultaneous low-res version of each shot than can be edited on low power computer systems and then swapped out for the full res version when the edit is complete. With this feature you could cut XDCAM HD on just about any old piece of junk computer! Likewise essence markers for metadata and tagging of shots are a superb platform for highly effective media management. But for most users of XDCamHD it's the simple things that make it a system of choice - discs are cheap, record times are long and, most significant of all, at the end of a shoot you have a physical source or archive master to put on the shelf. I know I'm not alone is being much reassured by that idea.

XDCAM is an 8-bit recording format and this is often cited as a major negative element in comparison to other tape-less systems that offer 10-bit acquisition options. In working practice it depends on the type of production as to whether this will be an issue of concern for you. If the project is a drama, TV series, short film or even low budget feature the lack of 10bit may impede options and performance when it comes to post-production processes such as color grading and visual effects where extra sampling headroom can make for cleaner mattes and color tone adjustments. If however the production is more documentary, ENG, news and less drama-based broadcast production, then the lack of 10-bit is arguably irrelevant.

The only other major criticism leveled at XDCamHD is the MPEG-based long GOP compression scheme. For some users long GOP is the great evil of modern production but the truth is that many of the concerns over long GOP are nothing more than speculative inaccuracies. Motion artifacts and smearing, often quoted as the result of long GOP, are in fact more readily the result of poor lighting and shutter selections. Fears over Long GOP really are largely unfounded and the continuing and growing widespread industry support for MPEG for acquisition and delivery is some proof of these concerns being put to rest. Long GOP certainly has some issues but it is not the great boogeyman it's often made out to be.

XDCamHD EX/Express Card
XDCamHD EX is the new addition to the XDCam platform that Sony has announced will be hitting the shelves in the coming year. And while the recording specs remain the same as XDCAM HD, the recording medium changes to that great buzzword of contemporary production - Solid State/Flash Memory. XDCamHD EX will use new Express Card technology and is obviously Sony's direct attempt to answer the popularity of Panasonic's P2 format.

Pros

  • XDCamHD EX includes all the extra features of its disc-based cousin essence markers, MXF metadata, simultaneous proxy file recording
  • Because it uses a newer bus transfer architecture, EX cards can shift HD video data from the card to the computer much faster than other current Flash Memory formats such as P2.

Cons

  • Unlike disc-based XDCAM there is no robust and shelflable master with the EX format
  • As with all solid state flash memory formats the cost per minute record times are still in the realms of the ridiculous by comparison with disc and tape
  • XDCam HD EX uses the same long GOP compression structure and 8-bit color space so it carries the same potential issues for post-production intensive projects

 

ExpressCard

XDCamHD EX shares all the specs of its disc-based sister; MPEG-2 IMX, 18, 25 and 35mbps. The no-moving parts of solid state allow for smaller and quieter cameras and Sony already have announced a new XDCamHD EX camcorder that seems to sit somewhere between the HDV V1 and the XDCAMHD F330. It has the potential to be the perfect in-between price point for a large array of productions looking for maximum bang for buck in a portable camera.

The Cons of HDCamHD EX are those of all current solid state systems - cards are still monstrously expensive. Similarly as with other flash memory recording there is no shelfable or physical master at the end of a shoot and you'll need meticulous processes in place in your workflow for copying and backing up footage if you want to be safe with your source master. Nothing should make any producer more nervous than the only copy being on a computer hard drive.


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Mike Jones is a digital media producer, author, educator from Sydney, Australia. He has a diverse background across all areas of media production including film, video, TV, journalism, photography, music and on-line projects. Mike is the author of three books and more than 200 published essays, articles and reviews covering all aspects of cinematic form, technology and culture. Mike is currently Head of Technological Arts at the International Film School Sydney (www.ifss.edu.au), has an online home at www.mikejones.net and can be found profusely blogging for DMN at www.digitalbasin.net


Related Keywords:HD acquisition , tapeless formats, Long GOP, wavelet codecs, intra-frame codecs


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