要創(chuàng)建響應式全屏視頻背景，需使用固定定位和object-fit屬性確保視頻覆蓋整個視口且不扭曲；1. 使用position: fixed將視頻容器固定在視口；2. 通過object-fit: cover保持視頻寬高比並覆蓋容器；3. 用z-index: -1將視頻置於內(nèi)容後方；4. 添加autoplay、muted、loop和playsinline屬性以支持自動播放；5. 為移動設備或慢速連接提供背景圖作為降級方案；6. 優(yōu)化視頻文件大小和格式以提升性能，最終實現(xiàn)跨設備兼容的全屏視頻背景效果。

Creating a responsive full-screen video background with CSS is a common design choice for modern websites. The goal is to have the video cover the entire viewport, scale properly across devices, and not distort the aspect ratio. Here's how to do it effectively.

Use position: fixed or object-fit with proper containment

The most reliable way to achieve a full-screen video background is by using a dedicated <video></video> element and styling it so it fills the screen while maintaining its aspect ratio.

1. HTML Structure

 <div class="video-background">
  <video autoplay muted loop playsinline>
    <source src="background-video.mp4" type="video/mp4">
    Your browser does not support the video tag.
  </video>
</div>

<div class="content">
  <h1>Welcome to My Site</h1>
  <p>This content is on top of the video.</p>
</div>

2. CSS Styling

 body, html {
  margin: 0;
  padding: 0;
  height: 100%;
  overflow: hidden; /* Prevent scrollbars */
  font-family: Arial, sans-serif;
  color: white;
}

.video-background {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  z-index: -1; /* Send video to the back */
  overflow: hidden;
}

.video-background video {
  position: absolute;
  top: 50%;
  left: 50%;
  min-width: 100%;
  min-height: 100%;
  width: auto;
  height: auto;
  transform: translate(-50%, -50%);
  object-fit: cover; /* Ensures the video covers the area without stretching */
}

Key Points to Understand

• object-fit: cover is crucial — it makes the video fill the container while preserving its aspect ratio, cropping if necessary.
• position: fixed on the container keeps the video locked to the viewport, even when scrolling.
• z-index: -1 places the video behind other content, so your text or UI stays visible.
• transform: translate(-50%, -50%) centers the video perfectly.
• playsinline is important for mobile Safari (iOS) to allow autoplay without full-screen mode.

Optional: Fallback for Slower Connections or Mobile

Some devices may not support video backgrounds well, or users may prefer reduced data usage.

 /* Optional: Add a fallback background image */
.video-background::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-image: url('fallback-image.jpg');
  background-size: cover;
  background-position: center;
  z-index: -1;
}

.video-background video {
  opacity: 0.8; /* Slight fade to improve text readability */
}

Or, disable video on mobile via media queries:

 @media (max-width: 768px) {
  .video-background {
    display: none;
  }
  body::before {
    content: '';
    position: fixed;
    top: 0; left: 0;
    width: 100%; height: 100%;
    background: url('mobile-fallback.jpg') center/cover no-repeat;
    z-index: -1;
  }
}

Performance & Autoplay Tips

• Keep video file size small — compress with tools like HandBrake.
• Use .mp4 with H.264 — best browser support.
• Autoplay only works if muted — browsers block unmuted autoplay.
• Consider adding a "mute toggle" button for user control.

Basically, with object-fit: cover , proper positioning, and a few mobile considerations, you can have a sleek, responsive full-screen video background that works across devices. Just don't forget accessibility and performance.

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