How Disk Cache Impacts After Effects Preview Playback

Introduction

Preview playback is a core function of After Effects that compositors, motion graphics artists, and video editors use to view their work within a composition. When the system can render frames and play back the composition in real-time, playback generally goes unnoticed because the work displays without lag or interruption. Any disruption that breaks the visual flow makes it harder for artists to assess their work.

Before After Effects version 25.2, rendered frames within a composition were loaded directly into system memory (RAM) for Preview playback. Two issues stemmed from this function. First, the total number of frames that could be played back was limited by the amount of available memory. Second, once RAM was full, older frames had to be overwritten, so viewing other parts of the composition required re-rendering and reloading them into memory.

In version 25.2, Adobe added the feature “Enable Preview from Disk Cache,” also known as High Performance Preview Playback (HPPP). HPPP stores every rendered frame from a composition in disk cache before streaming it into RAM for Preview playback. During playback, frames are read from RAM whenever possible. However, if memory cannot hold the entire composition, frames are continuously streamed from disk to memory instead. This allows Preview to play longer or higher-resolution compositions, provided the system can stream cached frames from storage into RAM fast enough.

There is another new feature in After Effects Beta version 26.0 that compresses each rendered frame in a lossless format before writing it to disk. These compressed frames are roughly half the size of uncompressed ones, reducing disk cache usage and allowing artists to store more frames within the same storage capacity. There is a performance trade-off when using compressed frames because playback now involves both the CPU and the disk cache. The CPU compresses the rendered data as it is written to disk and decompresses it when loaded for playback, while the cache disk transfers this data into RAM. By comparison, playback of uncompressed frames relies solely on disk read and write speeds. This feature was not specifically tested, but it is worth noting for artists considering enabling it and how it might impact playback performance.

While HPPP manages where rendered uncompressed and compressed frames are stored, the actual data produced by each frame, which is determined by the resolution, frame rate, duration, and bit depth of a composition, ultimately determines how effective this feature is for supporting real-time Preview playback. The size of each frame will determine how quickly the disk cache must write and stream frames to memory, as well as how much RAM is required to hold frames for playback. If disk cache throughput cannot keep up, playback will be laggy. At the same time, insufficient amounts of RAM will trigger HPPP to stream cached frames from disk to RAM, which has limitations based on composition settings and the technical capabilities of the disk drive. Understanding these limits enables After Effects artists to recognize how RAM and storage independently affect Preview playback, allowing for more informed hardware decisions based on their project requirements.

Storage and RAM Requirements

Each rendered frame in an After Effects composition contains a specific amount of data determined by its resolution and bits per channel (BPC). The size of these frames, combined with the composition’s frame rate and duration, dictates how much storage is required for the disk cache and the read/write bandwidth needed to maintain real-time Preview playback.

Adobe gives this mathematical formula for determining how much data is produced by a single uncompressed frame: 

(height in pixels) x (width in pixels) x (number of bits per channel) / 2,097,152

Using this formula, we created this table to show how much data (MB) a single frame produces at different resolutions and bits per channel (BPC):

Table 1 – Frame Data Sizes by Resolution and Bit Depth

Multiplying the size of a single frame by the composition’s frame rate (FPS) shows the theoretical data throughput required from the disk cache in megabytes per second (MB/s). The table below illustrates this for various resolutions, bit depths, and frame rates:

Table 2 – Bandwidth (MB per Second) by Resolution, Bit Depth, and Frame-Rate

To put this in context, here is a table showing the maximum read and write speeds of three specific drives representing Gen 5 NVMe M.2, Gen 4 NVMe M.2, and SATA SSD classifications. Please note that these are maximum rated speeds, and they may not be sustained over long periods of continuous reading and writing:

Table 3 – Maximum Read and Write Speeds of Modern Solid-State Drives

Depending on composition settings, the data throughput of rendered frames may exceed the sustained read and write speeds of the disk cache. When this occurs, HPPP cannot maintain consistent playback on its own, so frames must be stored in RAM to achieve real-time Preview playback at the composition’s resolution and frame rate. More available system memory allows for a greater number of frames to be stored, thereby reducing the reliance on the disk cache to continuously stream frames into RAM.

The table below shows the formula for calculating how much RAM is required to store one minute of a rendered composition based on resolution, frame rate, and bit depth:

( [desired seconds of playback] x [FPS] x [height in pixels] x [width in pixels] x [number of bits per channel] / 2,147,483,648 ) + 3

Table 4 – Memory Requirements for a 1-minute Composition Based on Resolution, Framerate, and Bit Depth

While the table above shows RAM requirements for a one-minute composition, the same data can be used to estimate the storage space it occupies on a disk. Here is a table that illustrates how many minutes of a composition can fit on a 2 TB disk cache drive across different resolutions, frame rates, and bit depths:

Table 5 –  Estimated Length of Composition Storable on a 2 TB Disk Cache by Frame Rate, Channel Depth, and Resolution

It’s important to note that very high-resolution or high-frame-rate compositions—such as 8K and 16K—may not perform reliably on a 2 TB drive, even if they are short duration and would only require a small number of cached frames. The sustained read/write speeds required for these compositions can exceed what the drive can maintain. In such cases, a larger-capacity drive is recommended, with at least 30% additional headroom to accommodate potential performance drops as the drive approaches full capacity.

While the information above provides a better understanding of where HPPP can operate effectively and when limitations may appear, it is still an estimation. In real-world use cases, the technical capabilities of storage and RAM can be influenced by additional factors such as drive I/O throughput, CPU performance, and software–hardware interactions, which may affect how HPPP manages frames or the performance of the disk cache drive.

Test Methodology and Results

To see how well these estimations translated into reality, we tested HPPP’s rendering of uncompressed frames using different composition settings, limited to 8 BPC and in Full resolution, using three different types of drives:

• 2TB Kingston FURY Renegade Gen 5 NVMe M.2 SSD
• 2TB Kingston KC3000 Gen 4 NVMe M.2 SSD
• 2TB Samsung 870 EVO SATA 2.5-inch SSD

Our goal was to determine if specific composition settings reached limitations based on the drive used for the disk cache and to verify whether the results aligned with the calculations and tables above. In this results table, the green check mark indicates acceptable real-time playback with HPPP, the orange RAM icon denotes compositions that rely on memory alone for real-time playback, and the red X marks settings that cannot achieve any real-time playback. Some may have minor playback latency, which is indicated by an asterisk. The X-axis consists of the different types of hard drives, while the Y-axis denotes the various resolutions and framerates that were tested:

Table 6 –  HPPP Drive Qualifications for Different Compositions at 8 BPC

Settings that were estimated to need lower bandwidth function roughly as expected, with the SATA SSD handling all three tested HD compositions. The M.2 drives were able to handle the 4K tests as well, but the Gen 4 version couldn’t provide smooth playback for the 8K 30 FPS composition despite being rated for higher maximum speeds. Likewise, the Gen 5 model couldn’t handle the 8K 60 FPS test. These are examples of how sustained read and write speeds on many modern drives are substantially lower than their maximum speeds, which should be taken into account when selecting components for an After Effects workstation.

High-Performance Preview Playback achieves real-time playback by streaming rendered frames from disk to memory, but it still has limitations that stem from the amount of data a composition produces and the storage drive’s ability to move that data into RAM fast enough to keep up. Once the resolution, frame rate, or duration exceeds what the cache drive can sustain, RAM becomes the primary source for real-time playback, and higher memory capacities are required to hold all frames within the composition.

For artists working on projects with lower resolutions and moderate frame rates, such as 8 BPC HD compositions at 24–60 FPS, a SATA SSD provides sufficient performance as a disk cache. This allows users to allocate a moderate amount of RAM for preview playback and direct remaining budget toward a faster CPU or additional memory and storage as needed.

As resolution, frame rate, and duration increase, particularly in 4K and 8K workflows, HPPP relies on faster disk speeds to maintain real-time Preview playback. For 4K 8 BPC compositions, a Gen 4 NVMe (like the Kingston KC3000) provides the read/write performance needed to support 24 to 60 FPS. To help determine the size of drive you would need for a disk cache, a 2 TB drive can hold roughly 17 minutes of 4K 60 FPS frames, while a 4 TB drive doubles that capacity to approximately 34 minutes.

For power users working in 8K at 30 FPS, a Gen 5 NVMe drive can sustain real-time playback using HPPP. However, in our testing, we found that this was the limit, and all other resolutions that exceeded 8K at 30 FPS would need to utilize RAM as the primary source for Preview playback. Systems should have at least 256 GB of RAM for 8K 30 FPS workflows, and a minimum 4TB cache drive is recommended, providing approximately 16 minutes of cached frames.

For projects exceeding 8K at 30 FPS, such as working with 8K RAW footage in a 60 FPS composition, maximizing system memory instead becomes necessary to sustain real-time playback. Workstations supporting 512GB or even more RAM will be necessary for these intensive workflows.

When configuring a new system or optimizing an existing setup for After Effects, it’s important to align your hardware choices with the demands of your projects. Understanding the resolution, frame rate, and bit depth of your compositions allows you to determine the appropriate RAM capacity and disk cache strategy, ensuring that Preview playback remains smooth and that HPPP can function effectively across different workflows.

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