FireWire Transfer

AJA's Io uses the IEEE 1394a 400Mbps FireWire port on a PowerMac for data transfer.

When Panasonic and Apple released support for DVCPRO50 (DV50) and talked about supporting DVCPRO HD, it became clear that FireWire had a wider role to play. Last year we saw FireWire support for the transfer of MPEG-2 TS (HDV) video introduced.

However, the most interesting application of FireWire is to use it to transfer uncompressed digital video with digital audio. Both Avid's Mojo (see January 2004) and AJA's Io use FireWire for this application.

To increase my understanding of this new application of FireWire, I installed an AJA Io on a dual 1GHz G5 PowerMac by connecting a FireWire cable between the Io and the PowerMac. How does Io transfer uncompressed video over FireWire? It uses the IEEE 1394a 400Mbps FireWire port on a PowerMac for data transfer. Because SDI (SMPTE 259) uses about 270MB/s, but only carries about 230Mbps/s, FireWire can easily handle the bandwidth. To accomplish this, an enhanced OS X FireWire driver had to be written.

When I installed the Io software, I was presented with a list of packages (see Chart 1). You likely will not install the PAL packages. If you are working only with analog video you only need the analog packages. However, if you are working with digital video you will probably want to install analog support. Is there any reason you would want to install the IoAnalogNTSC-Japan package? Absolutely. But only if you will have a need to input or output composite or S-video from/to a consumer/prosumer camcorder or deck that uses a 0IRE setup. I installed two packages: IoAnalogNTSC-US and IoAnalogNTSC-Japan.

If you have never worked with uncompressed video you really need to consider the performance of the hard disk(s) you plan use for media. AJA notes that, at the very minimum, to support a single video stream, the disk storage system must be able to provide and maintain a consistent 50MB/s read/write transfer rate between the PowerMac to disk. AJA also points out that FireWire drives, no matter how fast, cannot be used with AJA Io. Io connects to the host PowerMac via FireWire and uses most of the FireWire bus bandwidth. You can, however, attach and use FireWire drives on the PowerMac when Final Cut Pro is not in use. Their presence on the bus will not affect Io performance as long as they are not actively being used.

Specifically, AJA recommends the RAID solutions shown in Chart 2. If you do not have either type of RAID subsystem, do not even consider using an Io.

I attached a 2.5TB Apple Xserve RAID to the G5 using an Apple dual-channel Fibre Channel PCI card. The RAID had fourteen 250GB 7200-RPM SATA 100 disk drives. Each set of seven disks was grouped into a hardware-based RAID level 5 configuration and connected to one Fibre Channel. (RAID 5 provides data protection without requiring complete duplication of the drive contents. In the event of a drive failure, parity information can be used with data on surviving drives to reconstruct the contents of a failed drive. Parity data can be distributed across all the drives, providing much greater storage efficiency than mirroring — up to 85 percent for a set of seven drives.) The two RAID sets were then grouped into a RAID Level 50 software RAID to provide maximum read and write performance. Apple rates a RAID 50 Xserve RAID as providing more than a 360MB/s transfer rate.

Chart 3 shows the necessary transfer rate and storage requirements for various types of media. The Io uses either 8-bit or 10-bit uncompressed video, so the write performance needs be about 30MB/s. Realtime playback of each video stream requires up to 30MB/s. Thus, an Xserve RAID can transfer over 12 streams of 10-bit uncompressed video.

While both 8- and 10-bit uncompressed video provide broadcast quality video, 10-bit offers significantly higher quality (see “Compression Refresher” p. 47). Because 10-bit video has four times the numerical precision when compared to 8-bit, it has a signal-to-noise ratio 12 dbs higher than 8-bit video. With 8-bit video, there will be visible contour lines, or striations, that are particularly noticeable in scenes having soft gradients like a sunset. Even if the input and/or output video will only be 8 bits, a 10-bit project will offer higher quality. Industry standard professional mastering formats — Sony Digital Betacam and Panasonic D5 for High Definition — are both 10-bit formats.

Your PowerMac must also meet minimum performance requirements. Only these systems can be used: dual 800MHz G4, single 933Mhz G4, and G5-based PowerMac. I would not recommend using less than 1GB of RAM.

The Io has dozens of connectors. Two BNC loop-through connectors allow you to synchronize Io to your house reference video signal. When Io outputs video, it locks it to the reference signal, if present.

A BNC connector also supports composite video input. Composite video signals are digitized with 10-bit resolution. Io uses a 3-line adaptive comb filter to separate luma and chroma. (The Io LA uses an adaptive 5-line comb.) The S-video (4-pin, mini-DIN) input is digitized with 10-bit precision with 2X oversampling.

Three BNC jacks input RGB or YPbPr video. (AJA warns that RGB to YPbPr transcoding involves a level translation that results in a mathematical round-off error.) Within Final Cut Pro, RGB can be configured in the Audio/Video Settings or Easy Setups menus. Io supports three types of YPbPr video: SMPTE/EBU-N10, Betacam (NTSC), and Betacam (NTSC Japan). These three formats differ in levels and are configured in Final Cut Pro within the Audio/Video Settings or Easy Setups menus. I used the SMPTE/EBU-N10 setting with a JVC D-VHS deck that supplied 480i analog component video. Component video signals are digitized at 10 bits with 2X oversampling.

Two BNC connectors are provided for SDI — one for input and one a looping output. The SDI input supports 8-bit and 10-bit video plus up to eight channels of embedded 48kHz, 24-bit digital audio.

One female XLR connector is provided for channel one and two AES/EBU audio input, while another female XLR connector carries channels three and four. AES/EBU signals are handled by Io internally as 24-bits, 48kHz data.

Four analog audio input connectors, one for each channel, support either balanced XLR or unbalanced TRS-type connections. Analog audio signals are digitized by Io to 24-bit, 48kHz digital audio. With Io, 0 VU is 20dB below full-scale digital, and full-scale digital represents an analog level of +24dBu.

The optical TOSLINK connector uses a fiber-optic cable to carry 8-channel ADAT audio into Io. ADAT signals are input as 48kHz, 24-bit digital data.

Beautiful blue LEDs display the Video Input (SDI, component, S-video, composite) and the Audio Input (SDI, ADAT, AES/EBU, analog) that has been selected by Final Cut Pro. The Video Present and Audio Present LEDs indicate that a signal that have been selected is present. Mode LEDs indicate whether Final Cut Pro is configured for Input or Output. The Io box's look is a perfect match to a G5 and an Xserve RAID.

When you input 4:2:2 uncompressed video you can direct it to a disk file or software compress it to any QuickTime codec. Obvious space-saving formats include Photo-JPEG (OfflineRT), DV25, and DV50. With a frame-accurate deck, a finished Sequence can always be recaptured at full quality.

With regard to output ports, the 4:2:2 uncompressed digital video and 48kHz digital audio outputs from Final Cut Pro are made available simultaneously at all output ports. This means you do not have to worry about enabling output settings.

A 4-pin, mini-DIN ouputs S-video and a BNC connector outputs composite video. To generate either signal, 12-bit D/A converters (8X oversampling) are used. BNC connectors are also provided for two SDI outputs. SDI supports 8-bit and 10-bit video plus 8-channel, embedded 48kHz, 24-bit digital audio.

Three additional BNC jacks output either YPbPr or RGB. Three 12-bit D/A converters (8X oversampling) are used to generate the analog output. YPbPr provides headroom for superwhite and superblack, so video levels will be clipped when transcoding to RGB. (YPbPr to RGB transcoding involves a level translation that results in mathematical round-off error.) Io supports SMPTE/EBU-N10, Betacam (NTSC), and Betacam (NTSC Japan) output.

One male XLR connector is provided for the output of channel one and two AES/EBU audio, while another male XLR connector carries channels three and four.

Four male balanced XLR jacks handle analog audio output. Four 24-bit, 48kHz D/A converters are used to generate analog audio. With Io, you should adjust audio levels in Final Cut Pro (using the Master Level sliders) so peaks hitting 20dB read at 0 VU on an analog meter. A DB25 female connector on Io provides attachment for a balanced analog, 8-channel TASCAM DA-88/DA-38 style audio cable. Depending on the cable used, the other ends break out into eight separate TRS or XLR connectors.

Io's optical TOSLINK connector carries 8-channel ADAT 24-bit, 48kHz audio output. A BNC Audio Word Clock connector can be used to provide synch for an external DAT or an audio workstation.

A female DB9 connector provides a connection for VTRs, camcorders, disk media servers, and other devices using RS422 SMPTE (Sony) protocol. However, FireWire can be used to control a camcorder or deck. I created a custom setup to use this mode to control a JVC HDV camcorder while digitizing DV25 through a component analog connection.

Using Io with Final Cut Pro is very simple. A large set of Easy Setups comes with Final Cut Pro, and when you install Io, many more are installed. To use an Easy Setup, click on the pulldown menu and select the one you want. The choice will not take effect until you click the Setup button. That's it.

Final Cut Pro can output, via FireWire, uncompressed video when you playback a Timeline. To synchronize a PowerMac's audio output with analog or digital video output by Io: FCP System Prefs > Playback Control and set the Offset to seven frames. Now Io's video output should be in synch with the Canvas.

If you do not need to work with both analog and digital audio and video, you can choose from two other AJA products. The Io LA offers only analog I/O while the Io LD supports only digital I/O. Io LA supports composite, S-video, and component input (Genlock and RS-422 are also supported). Analog audio I/O is via a DB25 connector. Io LD supports SDI I/O plus a DB15 connector for a digital AV breakout cable, as well as a 2-channel, 24-bit, 48kHz, S/PDIF audio output RCA jack (Genlock and RS-422 are supported). The price for the Io is $2,290, and the price for Io LA/Io LD is $1,190.

I was very impressed by Io. AJA supplies a well-written, comprehensive manual to enable you to understand how to install and use Io. Excellent documentation is increasingly rare these days, and AJA is to be commended for expending the effort.

I found Io exceedingly easy to use. By using the supplied Easy Settings, working with uncompressed video was no different from working with DV. The quality, however, especially using 10-bit uncompressed video was fantastic.