How Lack of AVIF Progressive Rendering Hurts UX

Early implementations of the AVIF image format lacked progressive rendering, meaning images could not display a low-quality preview while the rest of the file downloaded. While AVIF delivers exceptional compression efficiency compared to formats like JPEG and WebP, the inability to render incrementally introduces a perceived performance penalty. This article explores how this technical limitation negatively affects visual feedback, perceived load speed, user engagement, and performance metrics.

The All-or-Nothing Loading Problem

In traditional progressive formats, such as Progressive JPEG, browsers render a low-resolution scan of an image almost immediately, progressively refining the details as packets arrive. Early AVIF decoders, however, operated on an "all-or-nothing" basis. Users had to wait for the entire image payload to download and decode before a single pixel appeared. This behavior leaves blank boxes or empty viewports during page load, which breaks visual continuity.

Perceived Performance vs. Actual File Size

User experience depends heavily on perceived speed rather than raw download times. Even though an AVIF file might be 30% to 50% smaller than an equivalent JPEG, a user staring at a blank space perceives the page as slower. Immediate visual feedback reassures users that content is arriving. Without progressive scans, users often assume the connection has stalled or that the website is unresponsive, leading to higher bounce rates, particularly on mobile devices with high latency.

Impact on Core Web Vitals

The absence of progressive rendering directly harms key performance metrics, specifically Largest Contentful Paint (LCP). Because LCP measures when the main visual content renders on screen, an AVIF hero image that does not display until fully transferred delays the LCP event. A progressive image, by contrast, can register an earlier paint event, improving both perceived speed and search engine ranking signals.

Mitigation Strategies

To offset the lack of native progressive decoding, developers must implement alternative techniques:

• Low-Quality Image Placeholders (LQIP): Inlining lightweight base64-encoded SVG or low-resolution blur images directly into the HTML to show immediate structure.
• Dominant Color Placeholders: Using CSS background colors matching the image to signal that content is loading.
• Strict Dimension Declarations: Enforcing width, height, and aspect-ratio in CSS to prevent Cumulative Layout Shift (CLS) while waiting for the full AVIF file to decode.

While newer revisions to the AVIF specification and modern browser engines are actively working toward layered, progressive decoding, the initial absence of this feature created a distinct trade-off between superior data compression and immediate visual feedback.