What Is the Maximum Frame Limit for Animated AVIF?

This article explains the maximum number of frames supported in a single animated AVIF file when using the reference library, libavif. It covers the limits imposed by the library’s code, the specifications of the underlying container format, and the practical constraints of rendering animated image sequences.

The Technical Limit in libavif

In the official libavif decoder library, the total number of frames in an animated sequence is tracked by the imageCount variable within the avifDecoder structure. In the C source code, this variable is defined as a standard signed 32-bit integer (int).

Because of this integer definition, the absolute maximum number of frames that the libavif API can theoretically index and report is 2,147,483,647 frames (which is \(2^{31} - 1\)).

Container and Specification Limits

An AVIF file is packaged using the ISO Base Media File Format (ISOBMFF) according to the Multi-Image Application Format (MIAF) specification. There are two primary methods for storing animations within this container, each with its own structural limits:

• Image Sequences (Track-Based): This is the standard method for animated AVIFs, where the animation is treated as a video track. The frame count is limited by 32-bit sample index tables within the ISOBMFF structure, allowing for up to 4,294,967,295 frames (\(2^{32} - 1\)). However, as noted above, libavif will cap its handling of these at the signed integer limit of 2.14 billion.
• Distinct Items (Item-Based): If an animation is stored as a collection of individual static image items rather than a continuous track, it is limited by the HEIF standard’s 16-bit item identifier. This limits the file to a maximum of 65,535 frames. Because this method is highly inefficient for long animations, track-based sequences are almost always preferred.

Practical Limitations

While the software and container specifications allow for billions of frames, practical hardware and performance limitations restrict animated AVIFs to much smaller numbers:

• Memory Usage: Decoding and playing back an AVIF animation requires system memory (RAM). Browsers and image viewers must buffer decoded frames, and exceptionally long animations will easily exhaust available device memory.
• File Size and Processing Power: Encoding billions of AV1-compressed frames requires immense CPU processing time and results in massive file sizes, defeating the purpose of utilizing a highly compressed web format.
• Application Constraints: Most web browsers (such as Chrome and Firefox) and operating system image viewers impose their own lower boundaries on image dimensions, file sizes, and frame counts to prevent system crashes and denial-of-service vulnerabilities.