解码Decode

解码是把编码数值还原成帧的过程——音视频流水线的第一步。

• 流水线三步：解码（数值→帧）→ 处理（缩放、色彩转换、滤镜、合成）→ 编码（帧→数值，写进容器）。
• 所有软件共用这条流水线：FFmpeg 在命令行驱动它；剪辑、调色软件是同一条流水线，多了做决定的界面。
• 要学的不是背步骤：是「该在哪一步做什么」的判断——按钮会变，流水线不会变。

Decoding turns coded numbers back into frames — step one of the audio-video pipeline.

• Three steps: decode (numbers → frames) → process (scale, colour-convert, filter, composite) → encode (frames → numbers, written into the container).
• Every app shares this pipeline: FFmpeg drives it from the command line; edit and grade apps run the same pipeline with an interface for making decisions.
• What you learn is not the steps by heart: it is the judgement of "what happens at which step" — buttons change, the pipeline does not.