上一篇里，云把电影存在远方的服务器上。可 💻 小电脑想看，还要整部下完？不用——流媒体让它边下边播。Last leaf, the cloud kept movies on faraway servers. Must 💻 Little Computer download a whole film before watching? No — streaming lets it watch while downloading.
第 1 步：切成小块，边下边播Step 1: Chop it up, play as it lands
先回答上面的问题：不等下完，怎么看到画面？靠切块和缓冲。To answer that: how do pictures show before the download ends? Chunks plus a buffer.
电影被切成小块，发一块播一块。浅色条是已缓冲的，深色是正在播放的。只要缓冲跑在播放前面，画面就不停。The film is chopped into chunks — each arrival plays at once. The pale bar is buffered video, the dark bar is what's playing. As long as the buffer stays ahead of playback, the picture never stops.
可同样追剧，为什么有人看 4K，有人却转圈？看网速和清晰度。But watching the same show, why does one get 4K while another gets the spinning wheel? Meet speed and quality.
流畅、高清、4K 是三档画质，越清晰越吃带宽。网速不够就降一档：先看得顺，再求看得清。Smooth, HD and 4K are three quality rungs — sharper rungs eat more bandwidth. When speed runs short, step down one: smooth first, sharp later.
录好的能切块，那直播呢？它播的是"现在"。Recorded shows chop nicely — but what about live? It streams "right now".
第 3 步：直播是现在的流Step 3: Live is a stream of right-now
主播现拍现发，服务器现收现分，观众几乎同时看到。慢几秒，但人人同步，这就是实时流。The streamer shoots and sends at once, the server receives and shares at once, and viewers watch almost together. A few seconds late, but everyone in sync — that's a real-time stream.
🎮 你来当带宽管理员（30 秒）🎮 Your turn: bandwidth manager (30 seconds)
道理讲完了。先拖网速滑块，看缓冲跑不跑得过播放；再连过 4 关，学会选档和断卡顿。Theory done. First drag the speed slider and see if the buffer outruns playback; then clear 4 rounds — pick levels and call the stall.
一句话记住它：流媒体 = 切块 + 边下边播 + 缓冲领跑；卡了就降档；直播是播"现在"的实时流。Remember it in one line: streaming = chunks + watch-while-downloading + a buffer in the lead; stall means step down; live is a real-time stream of "now".
边下边播：切小块发一块播一块，缓冲跑在播放前面Watch while downloading: chunks play on arrival, buffer stays ahead三档画质：流畅、高清、4K，越清晰越吃带宽Three rungs: Smooth, HD, 4K — sharper eats more bandwidth卡顿 = 播放追上了缓冲；直播是现拍现发的实时流A stall = playback caught the buffer; live is shot-and-sent real time
内容参考 OpenStax 等公开教材，多来源核对 · AI 生成、人工审核 · 发现错误欢迎指正，帮这片叶子长得更好。Based on OpenStax and other open textbooks, cross-checked across sources · AI-generated, human-reviewed · Spotted a mistake? Tell us — help this leaf grow.
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