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Posting HD: How Much Power Do You Need for Speed?
Posted Nov 8, 2007 Print Version     Page 1of 1
  

I the last year or so, I’ve shot about 25% of my projects in HD—mostly 1080i, but a couple of 720p jobs as well. While my final delivery format so far has been standard-definition DVD, I have experimented with a few things in post that have forced me to rethink my HD editing process.


Just because HDV cameras record to DV cassettes doesn’t mean that HDV will be as simple as DV to edit. While the HDV codecs give us great quality and convenience, it those benefits come at a huge price—namely, dealing with processor-intensive LongGOP MPEG-2, with its interframe compression scheme, when working with the footage in post.

In some respects, interframe compression is highly efficient. In a nutshell, interframe compression identifies redundancies among adjacent frames and creates groups of pictures (GOPs) in which one frame (known as an I-Frame) is complete; surrounding frames with redundant picture information are compressed by removing that information and compiled via reference to the complete I-Frame in its group. This is how interframe compression formats fit much higher-resolution images (i.e., frames containing more pixels and ostensibly much more visual information) on the same DV tape. DV recording uses a mild interframe 5:1 compression scheme. The DV codec compresses each frame individually. HDV compresses at about 47:1, using 15-frame GOPs, for the 1080-line, 60fps version (HDV 2); and 27:1, using 6-frame GOPs, for the 720-line, 30fps version (HDV 1).

So what does this mean to me, you ask? It means that when working with HDV footage in post, your computer is constantly trying to compile editable frames from frames that include only a portion of their own frame information, and thus needs to work a lot harder to process HDV natively than DV. Which raises the question: How powerful a system do you need to make HDV postproduction as smooth as DV editing is today?

From DV to HDV
I started editing DV in 1998 on a custom-built 200MHz Pentium Pro, with a Miro (later Pinnacle Systems) DV300 and Premiere 4.2. Editing DV footage with simple transitions and titles on that machine wasn’t too bad, but once you started with 3D transitions or color corrections, having to render meant time for a coffee break. I remember a single 3D BorisFX transition that took nine minutes to render. In 1999 I upgraded to a 500MHz P3, and then added a Pinnacle DV500 that allowed real-time analog preview on many 2D effects and filters, yet required rendering for FireWire output. In the next couple years there came a huge jump in speed with the Pentium 4s, and my next editing machine was a 2.4 GHz Compaq Evo 4000 workstation. After about a year I added a Matrox RT.X100 to it to become more efficient. In 2001, a 3.0 GHz HP xw4100 Workstation with another RT.X100 joined the family, replacing the 500 MHz P3 in the editing room. One of the reasons it was necessary to upgrade was that the software, while becoming more capable, was using more of the CPU for processing. In early 2005, Premiere Pro 2.0 was released, and the new NLE, in combination with the Matrox RT.X100’s software was taxing the 2.4 GHz machine to the point that I couldn’t get out a video over 15 minutes without it dropping frames.

I saw HD coming up fast, so I wanted to look for something that would be as close to future-proof as possible—a system that could handle DV today and HDV tomorrow. I settled on an HP xw8200 Workstation with a single 3.4 GHz Xeon CPU, with room for a second processor if needed. I transplanted the RT.X100 card from the 2.4 GHz Compaq to the new HP Xeon system without incident. The rendering performance in the DV projects jumped, where needed.

Then my Sony FX1 arrived. My HP xw8200 normally blows through most DV edits, but my first HDV clips were another story. Cuts and transitions were quick, but filters like RGB color correction took 48 minutes for every minute of footage to render in Premiere Pro 2.0.

Working with HDV meant that I was going to have to look at this from a new perspective. The sad reality is that HDV would humble most of the top edit workstations from even 18 months ago.

The Test and Test-Bed
In doing this study, I wanted to see what it would take to get the same smooth workflow that I had in DV with HDV. To find out, I looked at three different ways to post HDV footage to see which is the fastest and most efficient, and what it will cost. The choices we will look at all work within Adobe Premiere Pro CS3 and on the same test-bed system.

To run the tests, I used an HP xw8400 Workstation configured as follows:

• 2X 3.0 GHz Woodcrest (dual-core Xeon CPUs) with 4GB RAM
• ATI X1800XT 512MB graphics card (replacing the HP’s factory-installed Quadro FX1500)
• 16X DVD±R/RW DL burner
• Boot Drive 1: XP-32 80GB SATA
• Video RAID 0 (2X 160GB SATA)

On recommendation from Matrox, I replaced the factory-installed Quadro FX1500 with an ATI X1800XT 512MB graphics card. According to HP’s website, it should cost $5,300 and another $230 for the ATI graphics card (not available from HP). The editing configurations are Adobe Premiere Pro CS3 editing the HDV native, Premiere Pro CS3 using Cineform’s Aspect HD 5 "lossless" intermediary codec, and native HDV hardware-accelerated with Matrox’s RT.X2 card.

Comparing the Contenders
The cheapest solution at first glance is editing native with Adobe Premiere Pro CS3. But if you take into consideration that you’ll need all the power you can get, it may not be so inexpensive. Using the less compressed Cineform Aspect HD intermediary "lossless" codec, which converts your HDV video to a much more easily edited all-I-Frame stream (thus eliminating the math your CPU must constantly perform on GOP data), you can get away with using a much less powerful computer. Using the Cineform codec, you can preview much of your video in real time, and when it is time to export, render it back to HDV or other codecs. The extra $499 for the Cineform plug-in and whatever it would cost you for more hard drives to hold the larger files will generally cost less than the latest high-end workstation that native HDV editing will demand.

The most expensive solution is editing native with the Matrox RT.X2. Its strengths are that it previews almost everything in real time out to a DVI-D monitor or, through the breakoout box, it can go to an HD monitor or down-convert to a standard-definition analog NTSC (or PAL) monitor. That is a big savings over getting an expensive HD monitor on your edit desk. With the RT.X2, performance is scalable, meaning the more powerful the CPUs and the graphics card, the more you can do in real time. Keeping in mind that the RT.X2 software won’t install unless it detects two CPU cores in the computer, it gives you a lot of latitude if you want to sacrifice some performance for a much lower price.

Tale of the Test
All tests were done with the same footage and transitions. The only difference was that the footage was from the respective manufacturer’s codec. I captured HDV in Premiere Pro CS3’s codec, then used Aspect HD’s HD Link converter to convert the Adobe HDV to Cineform’s lossless intermediary codec, while keeping the originals.

There are two results reported for each test, a Preview render and an Export render. For "Preview," I hit the Enter key that allows for render and playback on the computer or external monitor. The Export render reflects the time it takes for the sequence to render for layback to tape. See Table 1, below, for complete results.

In my tests I tried to include a representative sampling of the types of edits and effects videographers may typically use in editing event videos. From the test results you can extrapolate how long renders and previews will take in one of the methods reviewed here. For instance, if you like to add a "film look" to your 5-minute recap with Premiere Pro’s Posterize time filter, on a system comparable to our test-bed HP, it will take about 15:55 (minutes:seconds) to render that section of the video.


figure 1
Test One: 5-Minute Video
This was a simple test of editing a few minutes of audio and video with transitions. Where Cineform or Matrox supplied their own transitions and effects, their transitions were used instead of Adobe’s. Here Matrox won the preview by 5 seconds over Cineform. However, on export to tape, Adobe won by 45 seconds.

Test Two: 1-Minute Photo Montage
In this test, I animated still frames over two Digital Juice backgrounds (uncompressed HD AVI). Handling still frames is a common task in event work. In this test all of the elements were exactly the same, with no proprietary codecs. Here we had the opposite results of Test One, with Adobe winning the preview render by 44 seconds and Matrox winning the export by 35 seconds.

Test Three: 1-Minute Color Balance
This clip involves color-balancing a 1-minute hi-def clip. Matrox and Cineform both did the job in real time. Adobe took 2:13. Matrox won on export to tape by 34 seconds over Cineform.

Test Four: 10-second RGB Color Correction
In this test, I color-corrected a 10-second video clip using Premiere Pro’s RGB Color correction filter. This filter’s controls work similarly to Color Balance, but the mechanics of the filter are so CPU-intensive in Premiere Pro that I ran only a 10-second test. That said, Matrox and Cineform tied with real-time performance, and Adobe took 2:37 to render those 10 seconds of color-corrected video.

Test Five: 1-Minute Posterize Time
Posterize Time is a great Adobe filter for making video look like film when adjusted to 24fps. In this test, Adobe won both preview and export. The preview was 2:10 faster than Cineform and twice as fast as Matrox. Export was 28 seconds better than Matrox and a 1:48 better than Cineform.

Test Six: 5-Minute Render to SD DVD
Matrox took this test, rendering a 5-minute clip to an SD DVD-compatible .m2t file, at 3:32, Premiere Pro CS3 at 4:21, and Cineform at 11:10.

Interpreting the Results
According to the data I collected, all three solutions had their benefits in price and performance. Really you can’t go wrong with any of these options for use with Premiere Pro CS3, given a decent system. It’s really a matter of how much real-time performance you want while editing.

On the surface, Adobe Premiere Pro CS3 doesn’t look much different from last year’s model (PP 2.0), but there is at least one huge difference under the hood: threading for multiple processors. I have a 30-second motion graphics test project that took 4:08 to render on my single Xeon 3.4 GHz HP xw8200 Workstation under Premiere Pro 2.0. Adding a second CPU sped it up by a whopping 7 seconds—not quite worth the $400 I spent on the second CPU. Trying it under CS3 with the second CPU, got the render time down to 2:20. Imagine that almost 50% speed increase applied to a longer project. If you are editing on a multi-core computer now, or if you will be in the future, upgrading from Premiere Pro 2.0 to CS3 will give you a major increase in rendering speed.

The Matrox RT.X2 is the most elegant solution of the three but also the most expensive once you add in the cost of a certified computer system. The board allows you to preview HD video on an external monitor as HD or down-converted to an SD monitor, which is a great benefit if you need to deliver in HD for some clients and SD for others. While some graphics cards may allow you to go out to an HD or SD monitor, it’s still not as good as having a dedicated card like the RT.X2. Even if you were able to preview the video, you wouldn’t get the acceleration you get with the RT.X2.

Cineform’s Aspect HD is a great enhancement that will work on many more computers and with much less powerful processors than the RT.X2. Aspect HD can potentially save you thousands of dollars over buying an expensive new computer. You will need about three times the storage space required by the more highly compressed HDV, and more time for exporting to HDV when your project is completed. But you’ll make up the time during the edit, with many real-time transitions and effects allowing you to get through the edit process more quickly. Since you generally don’t export to tape or render a movie until you are done editing, the fact that Cineform has long export and rendering times should not be an issue. Just let the longer projects render during a lunch break or overnight.

If you want to edit native HDV in Premiere Pro and hope to see something resembling real-time performance, you will need a much more powerful computer than when using Aspect HD. Editing HDV, unassisted by a board like the RT.X2, is a much slower process than editing DV. Editing DV in Premiere Pro CS3 is very snappy, but HDV can slow down your productivity to a crawl. I highly recommend adding either Cineform’s Aspect HD or the Matrox RT.X2, depen- ding on your editing workflow.

Marc Franklin (marcfvp at yahoo.com) has been shooting video since 1982, and has run Franklin Video Productions since 1992. He has been featured in the Hollywood Reporter, Forbes, and TV Technology; and has written for WEVA.



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