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Are the new iMacs good enough for video editing?

By Larry Jordan



A question I get asked all the time is whether the current iMacs (or, insert a computer model here) are "good enough" for video editing.

The answer is "Yes!" But, that isn't the right answer, because that isn't the right question.

In the past, the sheer horsepower of our computers was far less, so much so, that most computers could only play back video using smaller image sizes or lower frame rates. (Anyone remember watching computer videos that were 320x240? I remember building a business where the only videos we could create were that size.)

Today's computers can easily edit images, which are full HD (1920x1080), extending up into 2K, 4K, and, according to what I read in Post, 8K images!  (8K images sound amazing, but what actress wants to see her face with that much detail?  Make-up was invented for a reason.)

When you think about it, a 4K image is less than 16 megapixels, so the challenge isn't the image size; it's playing that many frames per second in realtime.

This gets me to the heart of the issue: any Mac, even a Mac Mini, has the horsepower to edit video. The real constraints are the speed of your storage, the complexity of your video codec, and the depth of your effects.

In the past, when many of us were editing standard definition DV video, we were working with FireWire 800 drives. DV video requires a data rate (that is, the speed of transfer between your hard disk and computer) of 3.75 MB/second. A FireWire 800 drive delivers around 80 MB/second, so everything was fine. (USB2, in comparison, only provided about 10-15 MB/second, which made it woefully slow for any serious video work.)

But as image sizes and frame rates escalated, the data rate of our hard disks became an issue. P2 media requires 15MB/second. ProRes 422 requires 18 MB/second. R3D files require 38MB/second. Uncompressed HD-CAM SR requires about 150MB/second.

Our poor FireWire 800 drive can't handle the load. And, unless you had a MacPro, you didn't have an option on anything faster.

That's why Thunderbolt is so exciting for Mac users and USB 3 to PC folks. Both these new technologies provide data rates 5-20 times faster than FireWire 800. The only hitch to these new formats is that they require a new computer that supports them. Oh, and drives that support the format as well. (The delays surrounding the release of Thunderbolt drives is worthy of a story in itself.)

(Side note on storage: A single hard drive, manufactured today, has a maximum data transfer rate of around 150MB/second. To take full advantage of the transfer speeds offered by USB 3 or Thunderbolt requires a RAID, which is a collection of hard drives all working together. To estimate the potential speed of a RAID connected via USB 3 or Thunderbolt, multiply the number of hard disks it contains by 100MB/second. USB 3 has a maximum speed of 480MB/second. Thunderbolt has a maximum speed of 1.1 GB/second.)

But the speed of our storage is only one issue. The next big gating factor is the complexity of the video codec. Camera manufacturers, in order to squeeze more data onto the relatively small storage that a memory card provides, are using highly efficient codecs (which stands for COmpressor/DECompressor, which defines the math used to reduce the size of video files) to squeeze video into every smaller spaces.
The problem is that these codecs, with names like AVCHD, H.264 and MPEG-4, create video that is extremely hard to edit. Video editing software has adopted two different ways to process these images: Adobe Premiere Pro CS6 off-loads the heavy number crunching to the GPU (Graphics Processing Unit, sometimes called the "graphics card") so that it can decompress the images fast enough to play and edit them in realtime.

Apple Final Cut Pro X (and, to a lesser degree, Final Cut Pro 7) converts the media, a process called "transcoding," into a more editing-friendly codec called ProRes 422. (While FCP X can edit video in its native format and does use the GPU, its first option is to transcode the media.)

The benefits to harnessing the GPU are that file sizes remain small and no time is lost for transcoding. The disadvantages are that color corrections occur in a more restricted space, final rendering and output can take longer, and not all Macs have graphics chips that are supported by Premiere Pro. So far, only the latest model MacBook Pros are supported by Adobe.

The benefits to transcoding are that any computer, regardless of its graphics chip, can efficiently edit transcoded media, effects and color correction are performed in a broader, more accurate color space, and overall system performance is improved. The disadvantages are that transcoded file sizes are much larger than the camera native files and time needs to be spent in transcoding. (Final Cut Pro X minimizes this extra time by transcoding files in the background, allowing you to edit in the foreground.)

The last big issue, and the only one where CPU speed really makes a difference, is in your effects. Most effects today are still CPU-based. Which means the more effects you add to a clip, the harder your CPU needs to work to create them.

Third-party developers are slowing enhancing their filters and effects to support GPU processing, which adds a huge boost of speed to calculating an effect.

Video editing remains one of the most challenging tasks we can do on a computer. But, more than just the computer is involved. When making a decision on what gear to get, keep the following thoughts in mind:

*    The speed of data transfer between your computer and your storage is the biggest determiner of system performance. Thunderbolt is better than anything. USB 3 comes in second.
*    Make sure the graphics chip is supported by your editing software
*    More RAM provides better performance than a faster processor
*    The fastest CPU is not, generally, worth the extra money. Go for the system in the middle of the range and invest more money in your RAM and storage

As editors, it is easy to get distracted by the speed of our CPU, or model of our computer. However, if you follow these guidelines, you can spend less money by paying attention to what really generates the best performance.

Larry Jordan is a producer, director, editor, author, and Apple Certified Trainer with more than 35 year's experience. Based in Los Angeles, he's a member of the Directors Guild of America and the Producers Guild of America. Visit his Website at http://www.larryjordan.biz

Posted By Larry Jordan on November 29, 2012 10:44 am | Permalink 
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