1. Understanding Core Web Vitals and Why They Matter
When it comes to improving your website’s performance, especially for SEO and user experience, understanding Google’s Core Web Vitals is a must. These are a set of specific metrics that Google uses to measure how users experience the speed, responsiveness, and visual stability of a web page. By optimizing images and videos — some of the heaviest elements on most websites — you can significantly improve your scores across these metrics.
What Are Core Web Vitals?
Googles Core Web Vitals focus on three key performance indicators:
| Metric | Description | Ideal Value |
|---|---|---|
| Largest Contentful Paint (LCP) | Measures loading performance by tracking when the largest visible element (like an image or video) loads. | < 2.5 seconds |
| First Input Delay (FID) | Measures interactivity — how fast a page responds after the user first interacts with it. | < 100 milliseconds |
| Cumulative Layout Shift (CLS) | Measures visual stability — how much the layout shifts unexpectedly during loading. | < 0.1 |
Why These Metrics Matter for SEO
Core Web Vitals are part of Google’s ranking signals under “page experience.” This means if your site doesn’t meet the recommended thresholds, you could lose visibility in search results — even if your content is great. Optimizing images and videos helps reduce load times and prevent layout shifts, which directly impacts LCP and CLS scores.
How Images and Videos Affect Core Web Vitals
- LCP: Large images or background videos often represent the largest visible element on a page, so their size and load time are critical.
- FID: Heavy media files can delay JavaScript execution, increasing input delay.
- CLS: If images or videos don’t have defined dimensions, they can cause unexpected layout shifts as they load.
The Bottom Line
If your website includes rich media like high-resolution photos or embedded videos, optimizing them isn’t just about saving bandwidth — its essential for hitting Core Web Vitals targets. The good news is, small changes to how you handle media can lead to big improvements in performance and rankings.
2. Choosing the Right Image and Video Formats for Faster Load Times
When it comes to boosting your website’s Core Web Vitals performance, choosing the right image and video formats plays a big role. Modern formats like WebP, AVIF, and MP4 offer better compression without sacrificing quality, which means your pages load faster and provide a smoother experience for users.
Why Format Choice Matters
Large media files can slow down your site significantly, especially on mobile devices or slower connections. By using optimized formats, you reduce file sizes while keeping visuals crisp and professional. This directly impacts metrics like Largest Contentful Paint (LCP) and First Input Delay (FID), which are key parts of Core Web Vitals.
Best Image Formats for Web Optimization
The table below compares some of the most common image formats used online today:
| Format | Compression | Quality | Browser Support | Best Use Case |
|---|---|---|---|---|
| WebP | Excellent | High (lossy & lossless) | Chrome, Firefox, Edge, Safari 14+ | Main images, thumbnails, product photos |
| AVIF | Superior (better than WebP) | Very High (even smaller file sizes) | Newer versions of Chrome, Firefox, Safari | Banners, hero images, high-res visuals |
| JPEG/PNG | Poor to Moderate | Mediocre to High | Universal support | Email previews, fallback content |
The Go-To Video Format: MP4 (H.264)
If youre embedding videos on your site, MP4 with H.264 codec is still the best choice for most use cases. It strikes a great balance between quality and file size and works across all major browsers without needing extra plugins.
Main Benefits of Using MP4:
- Saves bandwidth: Compressed but high-quality video delivery
- Smooth playback: Works seamlessly on desktop and mobile devices alike
- No compatibility issues: Widely supported across platforms and browsers
A Quick Tip on Responsive Media Loading
No matter what format you choose, always use responsive techniques like <picture>, <source>, or lazy loading attributes (<img loading="lazy">) to ensure assets load only when needed. This reduces initial page weight and helps improve metrics like Cumulative Layout Shift (CLS).
The Bottom Line on Format Selection:
Selecting modern media formats like WebP for images and MP4 for videos can drastically cut down load times. These choices align well with Googles Core Web Vitals metrics by improving speed without lowering visual quality.
This strategic shift not only boosts performance but also enhances overall user satisfaction—an essential goal for any successful website.
3. Implementing Lazy Loading for Visual Content
Lazy loading is a smart technique that delays the loading of images and videos until they are actually needed — meaning, until a user scrolls to them on the page. This helps reduce the initial load time of your site and plays a big role in improving Core Web Vitals, especially Largest Contentful Paint (LCP) and First Input Delay (FID).
Why Lazy Loading Matters
When a webpage loads, it traditionally tries to load all images and videos at once, even those that are far down the page. This can slow things down significantly, especially on mobile devices or slower networks. With lazy loading, only the visuals in or near the users viewport load immediately. The rest wait their turn as the user scrolls.
Core Web Vitals Impact
Lazy loading directly influences key performance metrics:
| Metric | Impact |
|---|---|
| LCP (Largest Contentful Paint) | By deferring offscreen media, LCP improves because critical content loads faster. |
| FID (First Input Delay) | With fewer elements loading initially, the browser can respond to user interactions more quickly. |
| CLS (Cumulative Layout Shift) | If implemented properly with size attributes, lazy loading helps prevent layout shifts. |
How to Implement Lazy Loading
The easiest way to enable lazy loading for images and iframes in HTML is by using the loading="lazy" attribute:
<img src="image.jpg" alt="Example Image" loading="lazy"><iframe src="video.html" loading="lazy"></iframe>This method is widely supported in modern browsers and requires no extra JavaScript or plugins.
Best Practices for Lazy Loading
- Use native lazy loading: It’s simple and efficient for most use cases.
- Add width and height attributes: Prevent layout shifts by reserving space for media content.
- Prioritize above-the-fold content: Avoid lazy loading images that appear immediately on page load.
- Test performance regularly: Use tools like Google PageSpeed Insights or Lighthouse to ensure lazy loading is working effectively.
When Not to Use Lazy Loading
Avoid lazy loading for key visuals above the fold — like your hero image or banner video — since delaying these can hurt LCP rather than help it. Always balance performance with user experience.
4. Optimizing Image and Video Dimensions and Compression
Properly sizing your images and videos plays a huge role in improving your websites Core Web Vitals. When media files are too large or not optimized, they can significantly slow down page load times — especially on mobile devices. Let’s explore how to scale your media correctly and apply compression techniques that maintain quality while boosting performance.
Why Size Matters
Uploading full-resolution images or high-definition video without adjusting dimensions can lead to oversized files that waste bandwidth. Always match the display size needed for your layout — no more, no less. For example, if an image is displayed at 800px wide on the page, don’t upload it at 2400px wide.
Recommended Image Sizes by Use Case
| Use Case | Recommended Max Width | Format |
|---|---|---|
| Hero Banner | 1600px | WebP or JPEG |
| Content Images | 800-1200px | WebP or JPEG |
| Thumbnails | 150-300px | WebP or PNG |
| Icons/Logos (Transparent) | <200px | SVG or PNG |
Best Practices for Image Compression
- Use modern formats: WebP offers excellent quality at smaller file sizes compared to JPEG or PNG.
- Aim for balance: Compress enough to reduce file size but avoid visible quality loss. Tools like TinyPNG, Squoosh, or ImageOptim can help.
- Avoid double compression: If your CMS compresses images automatically, don’t pre-compress too aggressively.
- Lazily load below-the-fold media: This reduces initial page load time by only loading media when needed.
Sizing and Compressing Videos
YouTube-style HD videos can weigh hundreds of megabytes, which is a problem if embedded directly. Here’s how to keep things fast:
- Avoid auto-play unless necessary: It consumes resources before users even engage with content.
- Select appropriate resolution: Don’t host 1080p video if 720p delivers similar impact and faster performance.
- Add preload=”none”: to video tags so browsers don’t start downloading until the user clicks play.
- Create lightweight previews: Use a still image as a placeholder thumbnail instead of loading the whole video right away.
Video Optimization Summary Table
| Tactic | Description |
|---|---|
| Select Optimal Resolution | Avoid higher resolutions than necessary (e.g., use 720p instead of 1080p) |
| Lazily Load Videos | Add <video preload="none">, so video loads only on demand |
| Create Poster Thumbnails | Add a poster attribute to show an image before the video starts playing |
| Avoid Auto-Play for Backgrounds | This helps improve LCP (Largest Contentful Paint) score |
| Use Efficient Codecs (e.g., H.265) | Saves bandwidth while maintaining visual quality |
The Takeaway: Quality Without the Bloat
You don’t have to sacrifice beautiful visuals for speed. By resizing images and videos appropriately and applying smart compression techniques, you’ll deliver faster-loading pages that still look amazing — which means happier visitors and better Core Web Vitals scores.
5. Preloading and Priority Hints for Critical Visual Elements
When it comes to optimizing images and videos for better Core Web Vitals performance, especially Largest Contentful Paint (LCP), one of the most effective strategies is telling the browser which visual assets are important right away. This is where preload and priority hints come into play.
What Are Preload and Priority Hints?
Preloading lets you tell the browser to start loading a specific resource—like an image or video—as early as possible. Priority hints, on the other hand, give browsers an idea of how important a resource is compared to others, so they can decide how to schedule downloads more efficiently.
Why Use Them?
If your hero image or above-the-fold video is slow to load, your page’s LCP score will suffer. By preloading these key elements and marking them as high priority, you’re helping the browser understand what matters most for rendering the first screen quickly.
Example: Preloading a Hero Image
<link rel="preload" as="image" href="/images/hero.jpg" type="image/jpeg">This tells the browser to fetch the hero image as soon as possible during page load.
Example: Using Priority Hints with an Image
<img src="/images/hero.jpg" fetchpriority="high" alt="Main banner">The fetchpriority="high" attribute signals that this image is crucial for rendering and should be prioritized.
Best Practices for Preloading and Priority Hints
| Element Type | Action | Example |
|---|---|---|
| Hero Images | Preload + High Fetch Priority | <link rel=”preload” as=”image” href=”/images/hero.jpg”> <img src=”/images/hero.jpg” fetchpriority=”high”> |
| Above-the-Fold Videos (Poster) | Preload Poster Image | <link rel=”preload” as=”image” href=”/videos/poster.jpg”> |
| Main Backgrounds | Preload if Large & Visible Early | <link rel=”preload” as=”image” href=”/images/bg.jpg”> |
Tips to Avoid Common Pitfalls
- Avoid preloading too many resources—it can backfire and delay critical assets.
- Only use
fetchpriority="high"on one or two essential images or videos per page. - If using responsive images (
<picture>,srcset, etc.), make sure your preload matches the expected file format and size for most users.
The Impact on Core Web Vitals
By strategically using preload and priority hints, you help speed up how fast the largest visible content loads. This directly improves your LCP score, making your site feel faster and more responsive to visitors—especially on slower connections or mobile devices.
6. Testing and Monitoring Performance Improvements
Once youve optimized your images and videos, its important to test and monitor how those changes impact your websites Core Web Vitals. These metrics directly affect your SEO and user experience, so keeping an eye on them over time is key. Luckily, there are several free tools from Google that can help you measure your improvements.
Google PageSpeed Insights
This tool gives you a quick overview of your website’s performance on both mobile and desktop devices. It provides specific scores for Core Web Vitals like Largest Contentful Paint (LCP), First Input Delay (FID), and Cumulative Layout Shift (CLS). After optimizing your media files, run a new test to compare results and see if your scores have improved.
How to Use:
- Go to PageSpeed Insights
- Enter your URL and click “Analyze”
- Review the diagnostics and opportunities sections for image/video suggestions
Lighthouse in Chrome DevTools
Lighthouse is built into Chrome DevTools and allows you to run audits directly from your browser. Its great for testing changes in real-time as you make updates to your site.
Steps to Run a Lighthouse Audit:
- Open your website in Google Chrome
- Right-click anywhere on the page and choose “Inspect”
- Select the “Lighthouse” tab
- Select the categories you want to audit (make sure “Performance” is checked)
- Click “Analyze page load”
Web Vitals Chrome Extension
The Web Vitals extension is a lightweight tool that gives you real-time feedback on Core Web Vitals as you browse any site. Its especially useful for monitoring performance during development or after publishing updates.
Main Features:
| Metric | Description | Status Indicator |
|---|---|---|
| LCP (Largest Contentful Paint) | The time it takes for the largest visible element to load | ✅/⚠️/❌ |
| FID (First Input Delay) | The delay between user interaction and browser response | ✅/⚠️/❌ |
| CLS (Cumulative Layout Shift) | The amount of unexpected layout shift during loading | ✅/⚠️/❌ |
Troubleshooting Tip:
If youre not seeing the improvements youd expect, double-check that images are properly compressed, served in next-gen formats like WebP, and lazy-loaded where appropriate. Also confirm that video files are hosted efficiently with preload settings adjusted.
The combination of these tools helps ensure that your image and video optimizations are actually making a difference. Regular testing keeps your site fast, user-friendly, and aligned with Googles performance standards.
