Adobe After Effects - Manual (Page 199)

Units
Slider Minimum
To manually preview (scrub) video in the Timeline panel or go to a specific frame, drag the current-time indicator.
To scrub audio in the Timeline panel, Ctrl+Alt-drag (Windows) or Command+Option-drag (Mac OS) the current-time indicator.
To scrub audio and video in the Timeline panel, Ctrl-drag (Windows) or Command-drag (Mac OS) the current-time indicator.
If you stop moving the current-time indicator while keeping the mouse button depressed, a short section of audio loops.
To manually preview (scrub) only the frames that are already rendered and cached into the RAM cache, press the Caps Lock key before
dragging the current-time indicator. This prevents After Effects from trying to render other frames when you drag over or past them. This
technique is useful when you want to manually preview some frames that you rendered using RAM preview settings that used an option to skip
every other frame.
Audio panel options
During previews, the Audio panel volume unit (VU) meter actively displays audio volume levels. At the top of the VU meter, signals indicate when
the audio is clipping—a distortion that occurs when the audio signal exceeds the maximum level that the audio device allows.
To view the VU meter and levels controls in more detail, increase the height of the Audio panel.
Audio panel
A. VU meter B. Level controls C. Level units D. Audio panel menu E. Level values
Choose Options in the Audio panel menu to specify the following options:
Choose whether to display audio levels in decibels or in percentages. 100% equals 0 decibels (0 dB).
The minimum audio level to display in the Audio panel.
Additional tips and options for previewing
With all previewing methods—as with rendering to final output—a layer is only visible in rendered previews if its Video layer switch is
selected.
The following are some of the factors that influence the speed with which previews are rendered:
layer switches
Fast Previews settings
preference settings
composition settings.
Use the Resolution/Down Sample Factor setting menu which is one of the simplest and most influential of the preview settings controls. Choose a
value other than Full from this menu to see all previews at a lower resolution.
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