Configuring an iMac Pro for video editing

By Larry Jordan

Ever since Apple released the iMac Pro, my inbox has been clogged with people asking advice on how to configure their system. This article is designed to help you make more informed decisions when you don’t have an unlimited budget. Also, while the iMac Pro is designed for many different markets, I’m focusing here on digital media.

If money is no object, buy the top of the line. It will be blindingly fast, it will work great and you’ll have enormous bragging rights. But… if money IS an object, then you need to make trade-offs, balancing the performance you need with the money you have. The good news is that you don’t need to buy the top-of-the-line to get a system today that can meet your editing needs for the next several years.

Some background
When Apple rebuilt Final Cut to create FCP X, they focused on upgrading its underlying architecture to take advantage of coming advances in hardware. This includes an all-64-bit architecture, optimization for core technologies including Metal, tight integration with both CPU and GPU and the ability to take advantage of faster I/O — both to the processors and storage.

There are no optimizations in Final Cut, Motion or Compressor that focus specifically on the iMac Pro. Instead, Apple’s media apps take advantage of whatever technology or performance benefits are provided in the hardware. In other words, there are no new features in FCP X that appear if it is running on an iMac Pro. What does appear is faster performance.

This is from the Apple website, comparing the iMac Pro to the fastest Quad core iMac:

“The iMac Pro takes Mac performance to a new level, even when compared to our fastest quad-core iMac.”

  • Photographers can work with enormous files and perform image processing up to 4.1 times faster.
  • Music producers can export massive multi-track projects up to 4.6 times faster and use up to 12.4 times as many real-time plug-ins.
  • Video editors can edit up to eight streams of 4K video, or edit 4.5K RED RAW video and 8K ProRes 4444 at full resolution in realtime without rendering. The iMac Pro can also export HEVC video three times faster.

Keep in mind that Apple reports these performance numbers are based on: “Testing conducted by Apple in November 2017 using pre-production 2.3GHz 18-core Intel Xeon W-based 27-inch iMac Pro systems with 128GB of RAM and pre-production 3.0GHz 10-core Intel Xeon W-based 27-inch iMac Pro systems with 64GB of RAM, both configured with Radeon Pro Vega 64 graphics with 16GB of HBM2.”

Do You Really Need an iMac Pro?
Well, “need” is a relative term. If you principally work with SD or HD material, an iMac will be perfectly fine. The performance benefits of the iMac Pro don’t justify the expense. If you are hobbyist, no, you don’t need an iMac Pro. You might “want” one, but you don’t “need” one.

However, if the bulk of your work involves 4K or greater frame sizes, 360-degree VR, RAW files, or HDR, the performance benefits of this new system make it worth considering, because the design of the iMac Pro significantly speeds working with larger frame sizes, faster frame rates, more effects and more processor-intensive codecs (such as HEVC).

With that being said, let’s take a look at the specific components to see which ones make the most sense for video editing.

Display
The iMac Pro uses the same display technology as the 5K iMac. So everything you see on a current iMac looks the same on the iMac Pro:

– 5K display
– One billion colors
– P3 wide color gamut
– 500 nits

But, while the display of the iMac Pro is the same as an iMac, the display capability of the iMac Pro is greater:
– It can drive two other 5K displays or up to four other 4K displays.
– It has enhanced external connectivity and more Thunderbolt 3 ports (so you still have Thunderbolt ports left over for other accessories after connecting a display).

CPU
Before the shouting starts, let me say again that if money is no object, buy the top-of-the-line iMac Pro. However, for most of the editing that most of us are doing, we don’t need to buy the top-of-the-line system to get significantly improved editing performance.

The 8-core system is fine for most editing and compression. For example, H.264 compression takes advantage of a hardware encoder that is built into all current Macs. This hardware encoder is independent of CPU cores. However, there are benefits to more cores, especially when decoding and encoding heavily threaded codecs like ProRes or HEVC. Also, the 10-core system offers a higher Turbo Boost speed of 4.5GHz versus 4.2GHz for the 8-core CPU. This additional speed benefits rendering and exporting.

The 14- and 18-core systems are designed for applications other than video editing. I would invest my money elsewhere in the system because video editors will see greater benefits in upgrading RAM and GPU when using Final Cut Pro on an iMac Pro.

An exception to staying within a 10-core system is that editors using Red Raw media or working with multiple streams of ProRes — for example, multicam work — will see improved performance with higher-core systems.

I recommend 8 cores for general editing and 10 cores for multicam editing and RAW video workflows.

Performance vs. Heat 
One of the issues I’ve heard about the current Mac Pro is that it has a problem with heat under heavy load. What I discovered is that, even more than the Mac Pro, the iMac Pro internals are designed specifically to dissipate heat under heavy load.

Outside, the iMac Pro is millimeter for millimeter the same size and shape as a standard 27-inch iMac with Retina 5K display; outside of the space gray color and a few extra vents on the back. But, on the inside, it’s radically different.

One of the key things Apple was able to do is make the system all flash-based; 3GB/s of fast SSD is pretty darn fast! Switching to all flash allowed Apple to remove the 3.5” hard drive and use that large space for a dual blower design and a massive heatsink and heat pipe architecture.

This delivers 75% more airflow and 80% more thermal capacity, enabling far more CPU and GPU power in the box over a traditional iMac. It is also worth noting that it does all this while still being super quiet (it is an iMac, after all), letting you focus on your work.

GPUs
In general, cutting video tends to use more of the CPU while effects and graphics tend to rely more heavily on the GPU. Increasingly, both FCP X and Premiere rely on the GPU for more and more tasks. Also, the greater the VRAM, the better the GPU performance. Whether you use Motion, After Effects, Premiere or Final Cut, investing in the best GPU will be a wise choice.

While VRAM is important, it is not the only determinant of a superior graphics card. For example, the Vega 64 is significantly faster in addition to the larger amount of VRAM. Also, more VRAM offers benefits when working with large frame sizes, multiple video streams (i.e. multicam), multiple displays and complex motion graphics.

RAM
The 32GB default RAM is fine for virtually all editing. If, on the other hand, you run multiple applications at once — say FCP X, Motion, Compressor, Photoshop and a web browser — 64GB of RAM is better.

While there is value in more RAM beyond 6GB, you won’t get enough bang for your buck to justify the additional cost.

Storage
The iMac Pro ships with a 1TB SSD. I haven’t measured it, but it is probably way past blindingly fast. (Apple says 3GB/second!) The problem is that most media projects today far exceed 1TB in storage. You will need an external high-speed, Thunderbolt 3 RAID system for even medium-sized projects.

Video Compression
Unlike video editing, video compression has its own requirements for system resources. While this is worth its own article here are some thoughts.

Both H.264 and HEVC are relatively highly compressed formats. This compression, of course, leads to smaller file sizes, but the resulting compression requires more processing power. With H.264 and HEVC, decoding and most encoding actions are processed via dedicated H.264 hardware within the system.

A select set of custom H.264 encodes in Compressor may use the H.264 software encoder, which is threaded across multiple cores. So while ProRes encoding benefits from faster, higher-core CPUs, H.264 and HEVC are not similarly CPU bound. Also, it’s important to note that video compression often includes other operations including retiming, scaling, and color conversion — all of which use the GPU.

If you are interested in HDR, 8-bit HEVC does, in fact, support HDR. Still, 10-bit encoding is recommended for the highest quality HDR output when using the HEVC codec. The reason this is important is that current Macs only support hardware acceleration of 8-bit HEVC. This makes the iMac Pro about 3x faster in HEVC encoding than an iMac.

For 10-bit encoding, the HEVC software codec is threaded and can therefore take advantage of multiple CPU cores when encoding; more cores means faster video encoding.

Wait, What About the Mac Pro?
First, Apple has announced and reiterated that they are working on a new, modular Mac Pro. However, they haven’t announced specs nor a release date.

The current Mac Pro is getting long in the tooth. In terms of performance, the iMac Pro is a better choice.

That being said, there are still two reasons to consider the existing Mac Pro:
– You can add any monitor you want
– Many of the components inside are upgradeable

For me, while these benefits are not trivial, the hardware inside the system has not be upgraded in several years. If you are focused on video editing, the existing Mac Pro is not the best current choice.

Summary
Here are my two recommendations for an iMac Pro for video editing: A budget version and a top-of-the-line version for editors. (The mouse and keyboard come standard, so I make no recommendations about either of these.)

Budget Version:


Top of the Line

Here are two other configuration articles you may find useful:


Larry Jordan is a trainer, writer, editor, producer and director who’s been explaining technology since, well, forever.This article first appeared in his website: LarryJordan.com


2 thoughts on “Configuring an iMac Pro for video editing

  1. Jamie LeJeune

    The article mentions that the iMac Pro is a better choice for HDR, but there’s no additional processor or GPU intensive requirements imposed by HDR unless is it combined with higher K counts above HD. If one is working in HD, a regular iMac or Mac Pro can work in HDR just fine. I realize that most HDR mastering is done in 4K, but there’s no reason that has to be the case.

    Reply
  2. Larry Jordan

    Jamie:

    You are correct – an iMac will generally handle HDR with no problems. What the extra hardware on the iMac Pro does is: decrease render times, improve file handling for 10-bit and greater files, and allow smoother playback of camera native files. The real burden of greater bit-depth, larger frame size files is that the file sizes themselves become huge … and then, more huger. The iMac Pro is designed to improve file handling of very large files.

    It isn’t an issue of the iMac “can’t,” it’s an issue of the iMac Pro being smoother and faster.

    Larry

    Reply

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.