How AVIF Decode Buffer Memory Scales with Dimensions

When decoding an AVIF image, memory usage is determined by the uncompressed pixel dimensions rather than the compressed file size on disk. The active decode buffer memory footprint scales strictly linearly with the total pixel count (\(Width \times Height\)), which means memory requirements grow quadratically relative to linear increases in resolution. Factors such as color bit depth, chroma subsampling, intermediate YUV-to-RGB conversion buffers, and decoder multithreading directly multiply this baseline footprint.

The Baseline Calculation: Uncompressed Frame Buffers

AVIF is a container format for AV1-encoded still images. To display an AVIF image, a decoder must decompress the stream into raw pixel data.

The baseline memory allocated for the final rendered image is calculated as:

\[\text{Final Buffer Size} = \text{Width} \times \text{Height} \times \text{Bytes per Pixel}\]

• 8-bit RGBA: Requires 4 bytes per pixel (1 byte per channel). A standard 4K image (\(3840 \times 2160\)) requires approximately 33.18 MB of memory.
• 10-bit or 12-bit RGBA (HDR): Because modern operating systems and decoders typically unpack 10-bit and 12-bit samples into 16-bit integers in memory, these formats require 8 bytes per pixel (2 bytes per channel). The same 4K image in 10-bit HDR requires approximately 66.36 MB.

Doubling both width and height quadruples the pixel count, leading to an immediate fourfold increase in the buffer footprint.

Intermediate Decoder Buffers (YUV Representation)

AV1 decodes content natively in YUV color spaces rather than RGB. Consequently, the decoder must maintain an intermediate YUV planar buffer before outputting the final RGB frame. The size of this intermediate buffer depends on the chroma subsampling configuration:

• YUV 4:4:4: Full-resolution chroma. Requires 3 full planes. For 8-bit, this is 3 bytes per pixel; for 10-bit, it is 6 bytes per pixel.
• YUV 4:2:2: Half horizontal chroma resolution. Requires 2 bytes per pixel for 8-bit; 4 bytes per pixel for 10-bit.
• YUV 4:2:0: Half horizontal and vertical chroma resolution. Requires 1.5 bytes per pixel for 8-bit; 3 bytes per pixel for 10-bit.

In implementations where the decoder does not write directly to the target presentation buffer, both the intermediate YUV buffer and the final target RGB buffer must coexist in memory simultaneously. For an 8-bit 4K image using YUV 4:2:0, the active memory footprint during conversion is:

\[\text{YUV Buffer (12.44 MB)} + \text{RGB Output Buffer (33.18 MB)} = 45.62\text{ MB}\]

Tiling, Multithreading, and Film Grain Synthesis

Beyond simple width-by-height scaling, AVIF includes structural elements that add memory overhead proportional to the image dimensions:

• Tiling and Threading: AVIF supports spatial tiling, which divides a large image into a grid of independently decodable blocks. While this allows multi-threaded decoding, each concurrent worker thread may allocate its own scratchpads and line buffers. Highly tiled, ultra-high-resolution images increase peak allocation based on the number of active threads.
• Line and Scratch Buffers: The AV1 deblocking and directional filter stages require retaining several rows of pixel data in memory at a time. The memory for these reconstruction buffers scales directly with the width of the image.
• Film Grain Synthesis: AVIF allows encoders to strip noise and apply synthetic film grain on the client side via metadata parameters. Decoders that perform grain synthesis often allocate a secondary output frame buffer to apply the grain without corrupting reference data, effectively doubling the frame buffer footprint during the final pipeline stage.

Practical Scaling Overview

Because decode memory is tied directly to geometry rather than compressed file size, decoding a heavily compressed 100 KB 8K AVIF image will consume just as much runtime decode memory as decoding a 10 MB 8K AVIF image.