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The DVD Writer: HD Camcorders--Writable Blu-ray Disc vs. HD DVD
Posted Oct 18, 2005 Print Version     Page 1of 1

We all know that writable Blu-ray Discs (BD) store a lot more information than HD DVDs. But does it really matter? When it comes to employing them in next-generation high-definition (HD) camcorders, it certainly does.

Predictably, debate over the relative capacity merits of BD and HD DVD centers on truck-and-trade prerecorded 12cm discs. Single-layer (SL) HD DVDs hold 15GB and dual-layer (DL) 30GB while equivalent BDs accommodate 25GB and 50GB respectively. HD DVD's space deficit puts its promoters on the defensive insisting that, with advanced MPEG-4 AVC and VC-1 video compression, capacity is just fine for distributing TV shows and Hollywood movies. I'll leave that one for the industry politicians to duke out, but HD DVD's inferior capacity is most certainly a drawback for writable technology uses—especially blue laser HD camcorders that will rely on physically smaller 8cm discs.

Existing standard-definition DVD camcorders have limitations but still are popular, thanks to their tremendous convenience. Above all else, it's their ability to shoot ordinary 8cm discs that can be immediately taken to almost any DVD player or computer for viewing or editing that makes them so endearing. New devices which will add blue laser HD DVD or BD capabilities promise the same for HD filming.

DVD camcorders are most criticized, and rightly so, for offering only limited uninterrupted recording time. For example, depending upon the unit and video quality setting, only 18 to 60 minutes of continuous material can be fit on a disc. Thus, it's crucial that next-generation blue laser HD camcorders offer as much storage space as possible.

The DVD Forum has yet to define specifications for writable 8cm HD DVDs. When they finally get around to it, discs are expected to be 4.7GB (SL) and 9.4GB (DL) in size. In contrast, the Blu-ray Disc Association already lays out BD equivalents with considerably more spacious 7.791GB (SL) and 15.582GB (DL) sizes. There's even the future possibility of four (31.164GB), six (46.746GB) and eight-layer (62.328GB) types. Practically speaking, multi-layer discs of any description will be exotic and expensive for some time to come, so the more material that can be crammed on a single-layer disc the better.

To keep costs down, lower encoding/decoding overhead, and ease transfer among devices, next-generation camcorder manufacturers will likely employ MPEG-2 compression. As such, single and double-layer HD DVDs will continuously record roughly 33 and 66 min (720p) or 25 and 50 min (1080i) of material, while equivalent BDs will be far more compelling at 55 and 110 min (720p) or 42 and 84 minutes (1080i).

In addition to shooting video, most digital camcorders function as still-image cameras. With resolutions upwards of four megapixels, many camcorders take credible photos and, at the rate technology is advancing, it's not hard to envision HD models eventually doubling or quadrupling this quality. JPEG and other compression techniques help chop down files to manageable sizes but hobbyists increasingly prefer taking their pictures in raw formats. Raw files are desirable since they capture unprocessed information from the camera's sensor, thus acting as digital negatives that can be more extensively tweaked after the fact. But enormously sized image files result. For example, nine-megapixel photos create 5MB JPEGs but the same images balloon to 20MB or more in raw format. Obviously, with stills and video competing for the same storage space it doesn't take a lot of material to chew up a disc.

Undoubtedly, MPEG-4 AVC and/or VC-1 compression will become feasible at some stage to significantly increase the video recording times I've described. However, rival storage technologies will equally benefit. Given this cold reality, optical disc camcorders must offer as large a capacity as possible if they are to credibly compete with magnetic tape and, more menacingly, the quickly rising tide of flash memory and hard drive-based units. I'd hate to see the optical storage industry cede yet another market to its competitors for lack of foresight.

Hugh Bennett (, an EMedia contributing editor, is president of Forget Me Not Information Systems (, a reseller, systems integrator and industry consultant based in London, Ontario, Canada. Hugh is the author of Understanding Recordable & Rewritable DVD and Understanding CD-R & CD-RW, both published by the Optical Storage Technology Association (OSTA).

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