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DCP BlogrollEdit Review: AJA Video Systems Io HD
Mar 1, 2008 12:00 PM, Reviewer: D. W. Leitner
Breakthrough I/O box brings advanced connectivity to Mac users.
The AJA Video Systems Io HD marries the uncompressed HD I/O and up-/cross-/downconversions of the AJA Kona 3 card (no Dual Link HD-SDI or 2K, however) to Apple’s ProRes 422 codec.
Mention video I/O for the Mac, and chances are “Kona card” will enter the conversation — even among production people who know little about Mac-based editing. Such is the popularity and reliability of AJA Video Systems' inexpensive QuickTime-based, uncompressed 10-bit video-capture cards.
The three Kona card lines — LS, LH, and 3 — offer, respectively, I/O for SDI/analog, HD-SDI, and Dual Link HD-SDI for 2K. Street prices (from B&H Photo Video) range from $900 for the LS series to $2,500 for the Kona 3. $300 more gets you AJA's breakout box, 1RU high, for each card.
Taking a closer look, the high-end Kona 3 also enables hardware acceleration for DVCPRO HD and HDV, and it provides up-/cross-/downconversion between SD and HD with full SD/HD component analog output.
For those unwilling or unable to use PCI cards — laptop owners, for instance — AJA and Apple codeveloped a small family of standalone devices that connect to Macs externally via FireWire and merge the capabilities of Kona cards with the connectivity of a breakout box. AJA offers two versions of the devices, called the Io family, for less than $1,000 — the Io LD (10-bit SDI I/O) and Io LA (10-bit A/D, D/A) — as well as a full-fledged SD rackmount version called merely “Io” (about $2,000).
These are now joined by the Io HD, which marries the uncompressed HD I/O and up-/cross-/downconversions of a brawny Kona 3 card (no Dual Link HD-SDI or 2K, however) to the latest codec on the block, Apple's ProRes 422, embedded in the Io HD hardware.
ProRes 422 is, of course, the new reduced-bit-rate mastering codec Apple introduced alongside Final Cut Studio 2 at NAB 2007. It has full 1920×1080 or 1280×720 I-frame DCT, 4:2:2, 10-bit sampling, and variable-bit-rate compression, with transport bit rates of 220Mbps and 145Mbps. Apple boasted at NAB that, despite data rates less than those of uncompressed standard definition (SDI is 270Mbps), ProRes 422 is “indistinguishable” from uncompressed HD — and it plays from a MacBook Pro.
Apple blazed no new trails here. Once upon a time, Sony breathed more years of life into Digital Betacam tape transports (themselves adapted from consumer Betamax) by limiting the bandwidth of HDCAM's camera signal, then compressing it to fit a standard-definition footprint (the first use of 1440×1080). Avid similarly introduced its DN×HD compression in 2004 to enable the use of reduced-size HD signals in an otherwise SD environment. The DN×HD original bit rates were 220Mbps (10-bit and 8-bit) and 145Mbps (8-bit). At that time, there were various demonstrations showing how HD-video signals reproduced through 10 generations of DN×HD at 220Mbps suffered no noticeable quality hit. People were understandably impressed.
The Io HD offers HD-SDI, HDMI, component, composite, and S-Video connectors for video; four XLR channels, eight channels of AES digital, and a pair of RCAs for monitoring audio; and a 9-pin connection for RS-422 deck control.
But there's a distinction between DN×HD and the newer ProRes 422 that could prove significant to some. While both are DCT-based (i.e. they use checkerboard-like macroblocks to segment the video frame for compression), the older DN×HD is constant-bit-rate (CBR), while ProRes 422 is variable-bit-rate (VBR), sometimes called “smart” encoding. What's the difference? Digital tape decks and video transmission use CBR, which keeps the data rate constant whether or not the images vary in their amount of detail. In other words, constant bit rate/varying quality of compression. DVDs, by contrast, adopt variable bit rate/constant quality: MPEG-2's compression actively adjusts to the demands of the material. Ever wonder how a DVD averaging 4Mbps can look so good?
The Io HD leverages the faster bus speeds of FireWire 800, which is how it connects to a Mac. Along with greater file-transfer bandwidth, the Io HD also hikes required Mac hardware specs: At minimum, you'll need a Power Mac G5 Quad 2.5GHz, a four-core or eight-core Mac Pro 2.66GHz, or a MacBook Pro with an ExpressCard/34 card for a FireWire 800 bus or SATA controller. (G4 owners such as me are flat out of luck.) The reason for the ExpressCard/34 add-ons for the MacBook Pro is that the Io HD demands its own FireWire bus, and it won't share it with other peripherals such as drives, decks, or cameras — which are forced to occupy a separate FireWire bus when the Io HD is in use. In the case of a G5 Quad or Mac Pro, the easiest workaround is to add an inexpensive PCI-X and PCIe FireWire card.
