入点和出点In & Out Points

入点（In Point）和出点（Out Point）是给素材"划线取材"的两个标记——入点定开头、出点定结尾，只有两点之间的部分会被剪进时间线。

• I 和 O 打头：查看器里按 I 打入点、按 O 打出点，也可点走带控制条上的 Mark In / Mark Out 按钮。
• 先粗后精：播放中大致停住，再用 ← / → 一帧一帧修到精确位置。
• 时长看得见：源查看器左上角的时间码实时显示入出点之间的长度。
• 时间线也能打：在时间线上打入出点，用来圈定新片段要落下的位置和长度（见 three-point-editing）。
• 标错随时清：Alt-I 清入点、Alt-O 清出点、Alt-X 两个一起清（macOS 上是 Option 键）。

In and Out points are the two marks you use to "draw a line" around the usable part of a clip — the In Point sets the start, the Out Point sets the end, and only the part in between goes to the timeline.

• I and O do the marking: press I for an In Point and O for an Out Point in the viewer, or click the Mark In / Mark Out buttons on the transport controls.
• Coarse first, fine later: stop playback roughly where you want, then nudge one frame at a time with ← / →.
• Duration stays visible: the timecode at the top-left of the source viewer shows the length between your In and Out points in real time.
• Timelines take marks too: set In and Out points on the timeline to define where a new clip lands and how long it runs (see three-point-editing).
• Easy to clear: Alt-I clears the In Point, Alt-O clears the Out Point, Alt-X clears both (the Option key on macOS).