The Value of Adding More RAM for Video Editing

Jacek sent me an interesting question this morning:

Is it worth it to buy 128 GB memory for a iMac i9 2019 (I know this officially supported only 64 but tested with 128 and works fine) to work with FCP X with Apple ProRes / RED RAW / BMD 6.5K footage? Multicam, ProRES 422HQ encoding, H256 coding. Or 64 GB RAM will be enough?

Jacek’s question got me thinking about RAM, more accurately, it got me thinking about the cost/benefit ratio of adding RAM.

THE SHORT ANSWER

Adding more RAM:

• Helps to a point.
• Costs more money.
• Doesn’t hurt your computer or applications, provided your computer supports the amount of RAM you want to add.
• Requires more power, which is important if you are often running on batteries.
• Will benefit editing larger frame sizes, but may not make any difference in performance, based on media you are editing.
• Won’t make much difference in rendering or export. Those are CPU/GPU-based.

THE LONGER ANSWER

The way most NLEs work is that, during an edit, the software will load (“buffer”) a portion of a clip into RAM. This allows for smoother playback and skimming, as you drag your playhead across the timeline.

When a clip is loaded into RAM, it is uncompressed, allowing each pixel to be processed individually. This means that the amount of RAM used for buffering depends upon several factors:

• How much RAM you have
• The frame size of the source video clip
• The frame rate of the source video clip
• The bit-depth of the source video clip

This graph illustrates this. It displays the MB required per second to cache 8-bit video into RAM.

(Frame rates are calculated at 30 fps for all frame sizes. Each bar represents a single clip. Click to see a larger image.)

As you can see, RAM requirements skyrocket with frame size. Also, these numbers increase when you have multiple clips playing at the same time.

NOTE: These numbers also increase as bit-depth increases, however the proportions remain the same.

Here’s a table that illustrates the numbers behind the chart.

(Each pixel is stored using a 24-bit (3 byte) value; i.e. “8-bit video.” Click to see larger image.)

Obviously, you need more RAM as frame sizes increase or more clips are playing at once (for example, in a multicam edit). Also, most NLEs will load more of each clip into RAM, if the RAM is available.

But, what happens if you don’t have enough RAM? The NLE “swaps” or off-loads data from RAM to your startup drive. If your startup drive is a spinning hard disk, everything REALLY slows down, because spinning hard disks are VERY slow compared to RAM. If your startup drive is a late-model SSD, things slow down, but not as much, Because NVMe SSDs are very fast – not as fast as RAM, but pretty darn quick.

Essentially, RAM is about 10X faster than an SSD and 50X faster than a single spinning hard drive.

MONITORING RAM USE

Activity Monitor is a very helpful tool to help us determine our RAM usage.

NOTE: Type Shift + Cmd + U to open the Utilities folder. Double-click Activity Monitor to start the app.

Activity Monitor allows us to measure current activity in five key areas:

• CPU
• Memory (RAM)
• Energy
• Disk (local storage)
• Network (both Internet and other network-connected devices)

Click the Memory tab at the top to display all the currently-running applications and the amount of memory each is using.

The key section is at the bottom. The Memory Pressure graph helps illustrate the availability of memory resources. The graph moves from right to left and updates at the intervals set in View > Update Frequency. The current state of memory resources is indicated by the color at the right side of the graph:

• Green: Memory resources are available.
• Yellow: Memory resources are still available but are being tasked by memory-management processes, such as compression.
• Red: Memory resources are depleted, and macOS is using your startup drive for memory. To make more RAM available, you can quit one or more apps or install more RAM. This is the most important indicator that your Mac may need more RAM.

Here are definitions of the other statistics:

• Physical memory. The amount of RAM currently installed in your system.
• Memory used. The amount of RAM currently in use.
• Cached files. Memory that was recently used by apps and is now available for use by other apps. For example, if you’ve been using Mail and then quit Mail, the RAM that Mail was using becomes part of the memory used by cached files, which then becomes available to other apps. If you open Mail again before its cached-files memory is used (overwritten) by another app, Mail opens more quickly because that memory is quickly converted back to app memory without having to load its contents from your startup drive.
• Swap Used. The space used on your startup drive by macOS memory management. It’s normal to see some activity here. As long as memory pressure is not in the red state, macOS has memory resources available.

Your goal is to have as little red in the graph or as little Swap as possible. Why? Because while RAM is very fast, swapping files to the hard disk (even an SSD) is very slow and degrades the performance of your system.

If Swap is always a large number, your performance may benefit from using a system with more RAM.

EXTRA CREDIT

Here’s what these three additional categories mean:

• App Memory. The total amount of memory currently used by apps and their processes.
• Wired Memory. Wired memory is the part where the OS Kernel and other low level components, as drivers and virtual memory objects are stored. Specifically, information in RAM that can’t be moved to the Mac’s drive. The amount of Wired memory depends on the applications you are using.
• Compressed. The amount of memory in RAM that is compressed to make more RAM memory available to other processes. This is the last step before swapping RAM out to local storage.

THE “BEST” ANSWER

As we’ve seen, the amount of RAM you need varies, depending upon the type of editing you are doing.

• 8 GB RAM. You can edit with this amount of RAM, but editing performance may suffer for anything larger than 720p HD
• 16 GB RAM. Good for most editing.
• 32 GB RAM. My recommendation for editing 4K, 6K, multicam and HDR.
• 64 GB RAM. Potentially good for massive frame sizes, but not required.

Anything more than 64 GB of RAM won’t hurt, but you won’t see any significant improvement in performance; especially considering the cost of more RAM.

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