TECH TIPS
Like a Surgeon
Operating with Avid's Open-Standard Codec
by Patrick Ready
All the cutting jokes aside, feature film editing has a lot in common with surgery––both take place in a pressure-cooker, high-stakes, precision environment where the tools must work flawlessly. For an editor to consider a significant change in the process, it has to make good creative and economic sense. Editing in HD is one such advancement in the editorial process that has been steadily refined over the past three years, especially since the introduction several years ago of Avid’s DS Nitris System, which converts SD sequences to HD, and marked the debut of Avid’s DNxHD open-standard codec for multi-generation compositing with smaller storage and bandwidth requirements.
In 2005, Avid upgraded its Symphony Nitris system (which used the same interface as Media Composer), and made it friendlier to the cutting room with the additions of secondary color correction, uncompressed HD, higher real-time performance and other advanced features.
At our company, Pivotal Post, we’ve provided editorial support for many films using DNxHD, including Ocean’s 13, Outlander, Doomsday, 3:10 to Yuma, Leatherheads, Hellboy 2: The Golden Army, Miss Pettigrew Lives for a Day, Get Some and The Mummy: Tomb of the Dragon Emperor. We want to share with Editors Guild members our cost-saving approach to editing features in HD.
An HD editorial set-up may cost a bit more than an SD set-up, but eliminating the conform process altogether by simply editing in HD with Media Composer Adrenaline v.2.7.5 has represented a significant savings of time and money. No more locking picture three days before a screening.
Using DNxHD
DNxHD encoding offers a choice of 8- or 10-bit depth in three user-selectable
resolutions: DNxHD36, DNxHD115 and DNxHD175. All that really matters are the
numbers: 36, 115 and 175. They stand for the amount of megabits per second
(Mb/s) and more Mb/s means better quality. For comparison, uncompressed HD
is 1,519Mb/s.
Here’s a guideline regarding how much storage you will need, taking into account two channels of 24-bit audio and the overhead necessary on the hard drives (since you shouldn’t ever fill them up 100 percent):
DNxHD36: 3.2 minutes per GB (1.8Tb for 500,000 feet of film)
DNxHD115: 1 minute per GB (5.4Tb for 500,000 feet of film)
DNxHD175: 40 seconds per GB (8.2Tb for 500,000 feet of film)
Although DNxHD36 is the lowest resolution, it still looks very good. For screenings, however, it has not held up as well as DNxHD115. So if your decision is to use less storage and work in DNxHD36, you may need to re-digitize your cut in DNxHD115 for a screening. Otherwise, work in DNxHD115, and you’re ready for a digital cut at any time. Unfortunately, DNxHD175 uses too much storage to consider for offline and it is only a marginal increase over DNxHD115.
 Figure 1. |
 Figure 2. |
Shared Storage Options
We have tested two solutions for shared storage: Avid MediaNet 5.0 and Facilis’
Terrablock. Both systems are 4-gigabit fiber channel and can handle mixed
networks of Macs and PCs. Both also allow gigabit Ethernet clients to connect,
making it possible to connect laptops, and they both have protection in case
a drive fails, but each handles this differently.
We’ve found that Avid MediaNet is the preferred way to have a truly shared project. This integrates one project for all users to share––especially beneficial with four-plus users on one project. On complex visual effects films, this is a great benefit.
Avid’s protection scheme is to mirror your media, which means you’ll use half of your storage to do this. With an 8Tb system, you only get 3.5Tb of useable space after you take into account the spare drives and the mirroring. Facilis Terrablock is RAID-5 protected, which uses much less media to protect than mirroring. This method allows a 12Tb system to create 10.5Tb of useable space. Since there is no shared project, bins have to be sent across the storage network to be “shared.”
In both cases, a back-up on Firewire drives is recommended. This gives you a working back-up that can be used in an emergency.
The Right Equipment?
In general, picture editors still prefer to work on a Mac. The fastest Mac
that is qualified for DNxHD editing is the 8-core MacPro, which is much faster
than the fastest PC-qualified, the dual core 3.0GHz HPxw8200. Media Composer
2.7.5 now uses all those processors, unlike earlier versions that only used
one. The rule of thumb today is: More processors equals better performance.
Not long ago, 10Tb of storage cost as much as a Ferrari. Today, it is more like a Prius, and 50-inch 1080p plasma monitors, once only for the elite, were down in price over 60 percent in 2007 alone. For your dual Avid monitors, 23-inch Apple Cinema Displays are excellent, and for your full-screen third monitor, we like the JVC DT-V24L1DU because of its true 1080p picture, affordable price and multiple inputs. For a client monitor, the Panasonic 1080p 42-inch (TH-42PH10UK) and 50-inch (TH-50PH10UK) plasmas are great. Large plasma and LCD monitors have a 1.5 frame-delayed picture. To solve this, we use the Rane AD-22d effects processor to dial in the delay precisely. Also, make sure to get all your monitors calibrated so they match.
Your MacBook Pro or PC laptop can now run the full version of Media Composer. Although Avid has not qualified the laptop for working in HD, it does work––but with limited performance.
A screening room is easily set up and the Avid can drive it with excellent results. Some very powerful and inexpensive 1080p projectors are the Sony VPL-VW50 or the VPL-VW200. It’s usually no more expensive than renting a dailies server and projector from your telecine lab. An alternative to the projector is the Panasonic 65-inch 1080p plasma monitor (TH-65PF9UK); it sets up easier and the brightness and contrast cannot be matched on most affordable projection systems.
What formats should I use?
Transfer your film to HDCAM so you can use the inexpensive play-only Sony
J-H3 HDCAM deck if you want to digitize (or re-digitize at a higher resolution
later) in the cutting room. Next, set up your Avid project as 1080p/23.976
(see Figure 1). If you choose 1080p/24, the downconvert function will not
work and you won’t be able to make real-time outputs to SD media like
a DVD or VHS.
Set your audio project settings to 24-bit audio; otherwise it will default to 16-bit (see Figure 2). Record at 48.048kHz. If you bring your audio in separately from the picture, you can slip sync to make it perfect. When you import 48.048kHz audio into your 23.976 project, make sure not to convert it (see Figure 3). The Avid will re-stamp it to 48.000kHz so it will be in sync (without doing a sample rate conversion) and will remain pristine.
 Figure 3. |
Output Options
For screenings, the D5 format has been very standard, mainly because
it supports eight channels of audio, so you can do a discreet 5.1
mix. If you are doing a single-day rental, it can be delivered and
tested the afternoon before you need it and picked up the day after
you’ve used it. To output to DVD, you should render and turn
on the downconvert in the video output settings (see Figure 4). Once
you turn that on, the SD outputs of your Adrenaline hardware will
be active.
 Figure 4. |
If you need a frame-accurate SD output to DVCAM or BetaSP, first perform a video mix-down, then transcode to SD. Then you will output to SD as you normally do. Stay tuned on this topic, though. Avid now has a console command to turn off the transcode and it may come out as a permanent feature soon.
Conclusion
Once you take the plunge to edit in HD, you won’t look back. Your picture
looks great, your budget doesn’t suffer and the process is simplified.
Faster, better cheaper––now you can have all three.
Patrick Ready is the chief operating officer of Pivotal Post in North Hollywood, California (www.pivotalpost.com). He can be reached at patrick@pivotalpost.com
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