Keyframe
Keyframe (Intra-Coded Frame)
A complete, self-contained frame in a video that stores the full image data without reference to other frames, serving as a reference point for surrounding frames that only store the differences.
技術的詳細
Video compression uses three frame types: I-frames (keyframes, fully self-contained), P-frames (predicted from previous frames, store only motion vectors and residual differences), and B-frames (bidirectional, reference both previous and future frames for maximum compression). A GOP (Group of Pictures) is the sequence from one keyframe to the next. Shorter GOP intervals (more frequent keyframes) enable faster seeking and more resilient streaming but reduce compression efficiency. Streaming protocols require keyframes at regular intervals (typically every 2-10 seconds) for adaptive bitrate switching. Scene-cut detection inserts keyframes at visual transitions.
例
```html <!-- Keyframe: HTML5 video with format fallback --> <video controls preload="metadata"> <source src="video.webm" type="video/webm; codecs=vp9,opus"> <source src="video.mp4" type="video/mp4"> Your browser does not support HTML5 video. </video> ```