• Blogs
• Tradeshows
• Partners
• White Papers
• Events

Edit Review—Avid Mojo

Jan 1, 2004 12:00 PM, By Steve Mullen

I/O hardware also accelerates Xpress Pro.

I'll admit I was confused by Mojo when I first saw it at NAB 2003. Looking at the back of the small Mojo box, I could see a set of video input and output jacks — plus a four-pin and a six-pin FireWire connector. It looked like any of the dozen FireWire transcoder boxes on the market. The price, however, at $1,695 would have been way too high for such a box.

More than simply a hardware-based I/O solution, Avid's Mojo also accelerates the performance of Xpress Pro.

Equally confusing to me was the way Avid marketed Mojo as offering “the power of Avid DNA hardware.” Avid defines DNA as Digital Nonlinear Accelerators. Specifically, Avid describes DNA as “a powerful piece of hardware designed to dramatically increase the media-processing power available in today's leading personal computers.”

However, I couldn't find any information about the effects-processing chip that I assumed must be within. Moreover, I wondered, how are all the streams that are involved in a multiple-stream realtime timeline moved via FireWire? Avid's FAQ explanation is that “Mojo accelerates time-consuming media I/O and conversion operations.” This left me wondering if Avid was claiming that the DV codec chip within Mojo is responsible for the dramatically increased media processing power claimed for DNA. If this were the case, then every DV camcorder that can input and output analog video transcoded to/from DV would be a media accelerator.

Avid's claim that Mojo also handles uncompressed video only added to my puzzlement. Especially since there are no Y, Y-B, and Y-R connectors on Mojo. To help solve my puzzlement I drew a series of schematic diagrams.

Diagram 1: DV25 Input You can monitor the DV signal being captured by using Mojo's audio and video outputs.

DV25 Input

When you use Mojo as a way of capturing DV via the four-pin FireWire port on the back of the Mojo, the box acts an extension of the DV port on your computer. (See the violet path, Diagram 1.) In Xpress Pro's Capture dialog box you select the Mojo FireWire port via “Video: DV.”

Analog Input as DV25

When you need to input analog video, you'll use more of Mojo's circuitry — as shown in Diagram 2.

To gain access to analog input, select “Video: S-Video” for S-Video input or “Video: Composite” for composite. One item missing from Avid's Mojo literature is how the NTSC composite signal is separated into luma and chroma components. (Circuit A.) Checking with Avid, I found Mojo uses a 2D (three-line) adaptive comb filter fed from 10-bit A/D (analog-to-digital) converters. (Circuit B — within the same IC that includes Circuit A plus the A/D converters — separates the chroma signal into Y-B and Y-R components.) The digital Y, Y-B, Y-R signals are compressed to DV25 and sent to the host.

Analog Component Input as DV25

If you purchase a pair of cables from Avid, you can input and output analog component video to and from Mojo. The cables are incredibly simple, and Avid provides instructions on how to “roll your own.”

Diagram 2: Composite and S-Video Input as DV25.

The input Y signal terminates in an RCA plug that is plugged into Mojo's composite RCA input jack. (Mojo does not use BNC connectors for composite I/O.) The Y-B and Y-R signals terminate in an S-Video DIN plug that plugs into Mojo's S-Video jack. You request analog component video input by selecting “Video: Component.” Mojo then functions as shown in Diagram 3. The analog component signals are digitized to digital Y, Y-B, Y-R components that are compressed to DV25 and sent to the host.

This feature enables DV25 source files — which are much smaller than uncompressed video files — to be input from any VTR that supports analog component output. The obvious VTR option is a Sony Beta SP deck.

Mojo-Based Realtime Output

If this were all Mojo could do, then there are a number of cheaper transcoder boxes you could purchase. However, to understand how Mojo powers realtime effects, consider what happens as effects are generated. One or more DV-compressed streams are uncompressed by software into digital YUV 4:2:2 data. Effects are now rendered and displayed on your computer's monitor.

Diagram 3: Analog Component Input as DV25.

If you have requested that Xpress DV output DV25 from your computer's FireWire port, the rendered video mix is recompressed to DV via software. Since the computer must perform the compute-intensive DV compression task, there's little horsepower left to uncompress video and render effects in realtime. Therefore, the Xpress DV's realtime green light is turned off.

However, if the digital YUV result from rendering is sent — without compression — from your computer's FireWire port, all system compute power can be applied to performing realtime effects. The uncompressed digital video (plus digital audio) data from the FireWire port is accepted by Mojo, which functions as shown in Diagrams 4 and 5. The uncompressed YUV video is compressed to DV using Mojo's DV25 codec. DV is then output via Mojo's four-pin FireWire port.

Diagram 4: Realtime DV plus Composite and S-Video Output.

Uncompressed video that's sent to Mojo is also converted to analog output using 8-bit D/A converters. Composite and S-Video can be output as shown in Diagram 4. (Circuit D generates the chroma signal from Y-B and Y-R; Circuit C creates the composite signal from luminance plus chrominance.) Alternately, analog component can be output as shown in Diagram 5.

Analog component output enables a production to be recorded by DVCPRO50, IMX, and DigiBeta decks. Use Xpress Pro's Tools > Video Output Tool command to select Composite, S-Video, or Component output.

Now, as Avid proudly proclaims, you really can edit in realtime on a laptop. Moreover, this is not merely a realtime preview to an NTSC monitor — although, of course, this is supported. If, upon playing a sequence, no red (dropped frames), yellow (CPU maxed out), or blue (disk bandwidth limit reached) warnings appear during a preview playthough, you will be able to output with no rendering.

Another Mojo benefit is image quality. Video quality is maximized when DV material is combined with uncompressed graphics and output as uncompressed video.

Diagram 5: Realtime DV plus Analog Component Output.

Mojo's Field Programmable Gate Array (FPGA), which controls all I/O operations, has the ability to scale in realtime Avid's low-resolution (i.e., draft quality) video to full-resolution video. Therefore, after switching to draft mode, you not only can work with significantly more complex timelines in realtime, you can even record these “preview” quality sequences to tape without rendering.

Uncompressed (1:1) Video Input

If Mojo can accept uncompressed video from a computer, then it should be able to send uncompressed video to a computer. And Mojo does enable uncompressed digital 4:2:2 YUV video to be written to hard disk. Analog composite and S-Video can be input as uncompressed data as shown in Diagram 6.

Diagram 6: Composite or S-Video Analog (or DV) Input as Uncompressed Video.

Alternately, component analog video can be input, as shown in Diagram 7. And, as shown in Diagrams 5 and 6, DV can be input, if necessary, via FireWire as uncompressed video. (Not shown in these two diagrams is Mojo's ability to output analog audio and video during DV input.)

To input uncompressed video, after selecting the input source (composite, S-Video, component, or DV), select “Res: 1:1.” The option enables several capabilities.

First, depending on the power of your computer, one stream of uncompressed video can be edited as if it were DV25. Unfortunately, single-stream effects (filters) will not be realtime.

Second, uncompressed video can be used in a timeline with DV. Video that you plan, for example, to chroma-key can be input as uncompressed video. By working with uncompressed video, keying will be especially clean. The background can be DV or graphics.

Audio Input/Output

Mojo has RCA jacks for audio I/O. A simple XLR to unbalanced RCA plug can be used with pro VTRs. However, be sure to set the VTR output to -10dBu. Select analog audio input via “Audio: RCA (-10dBu)” instead of “DV.”

Additional Mojo Features

Diagram 7: Component Analog Video (or DV) Input as Uncompressed Video.

Mojo has a few more tricks up its sleeve. An RCA jack on the rear accepts a Genlock black burst. Additionally, Mojo has a 1/8in. stereo headphone jack on the front, plus a volume control. Mojo also includes an After Effects plug-in that enables AE preview on an NTSC monitor connected to Mojo.

Mojo has one huge shortcoming: minimal documentation. A CD-ROM explains how to connect video equipment to it — as if that were not obvious. Searching for “Mojo” using Xpress Pro's Help led to only a few items, none of much help. Ultimately, trial and error — plus a call to Avid — were my tactics to using Mojo. For the price, Avid should include a printed manual.

Ultimately, anyone purchasing Xpress Pro, rather than Xpress DV, really should purchase Mojo. I would love to see Avid sell a bundle priced at $2,999.

BOTTOM LINE

Company: Avid
Tewskbury, Mass.; (978) 640-6789
www.avid.com

Product: Mojo

Assets: Inputs and outputs DV and analog composite, S-Video, and component; accelerates digital effects; allows true realtime editing on a laptop.

Caveats: Poor documentation.

Demographic: Xpress Pro editors

Price: $1,695

© 2008 Penton Media, Inc.