Preview video and audio
You can preview all or part of your composition as you work, without rendering to final output. Many of the controls for previewing are in the Time Controls panel.
With
all previewing methods—as with rendering to final output—a layer
is only visible if its Video layer switch 
is selected.
Some factors that influence the speed with which previews are rendered include layer switches, Fast Previews settings, and composition settings. One of the simplest and most influential of the preview settings is the Resolution/Down Sample Factor setting at the bottom of the Composition panel; set this to a value other than Full to see all previews at a lower resolution.
To
turn pixel-aspect ratio correction on or off for previews, click
the Toggle Pixel Aspect Ratio Correction button 
at
the bottom of the panel. Because the scaling is not of high quality,
use pixel aspect ratio correction to evaluate shapes, not fine pixel
detail. (See Change pixel aspect ratio.)When possible, preview on the same sort of device that your audience will be using to view your final output. For example, you can preview on an external video monitor. To see your composition as it will appear on a mobile device—such as a mobile phone—first render your composition to final output, and then use Adobe Device Central to view the movie.
If color management is enabled, you can preview a composition, layer, or footage item as it will appear in the output color space. (See Simulate how colors will appear on a different output device.)
Use standard preview
Standard preview (commonly called spacebar play) plays video in the active Composition, Layer, or Footage panel from the current time. Standard previews play at a speed as close to that of real time as possible; however, for complex compositions, the speed of the preview may be much less than that of real time.
Click the Play button 
in
the Time Controls panel, or press the spacebar.Use RAM preview
RAM preview allocates RAM to play video and audio in the Timeline, Layer, or Footage panel in real time. The number of frames that can be stored for real-time playback depends on the amount of RAM available to the application and the settings in the Time Controls panel.
In the Time Controls panel, you can specify two sets of RAM preview options: RAM Preview Options and Shift+RAM Preview Options. For example, you may decide to set RAM Preview Options for full frame rate and full resolution, and set Shift+RAM Preview Options to skip one out of every two frames and preview at half resolution.
In the Layer and Footage panels, RAM previews play untrimmed footage.
- To modify RAM preview options, click the RAM Preview
Options menu in the center of the Time Controls panel and choose
RAM Preview Options or Shift+RAM Preview Options. You can change
any of the following:
- Mute Audio
- Include or exclude audio from RAM preview.
- Frame Rate
- Choose Auto to use the composition frame rate.
- Skip
- The number of frames to skip between each rendered frame. Choose 0 to render all frames.
- Resolution
- Choose Auto to use the composition resolution.
- From Current Time
- Select From Current Time to play from the current time; otherwise, RAM Preview will play the work area or from the beginning of the composition, layer, or footage item.
- Full Screen
- Play RAM preview at the full size of the composition, layer, or footage item on a screen that is the background color. You can change the panel’s background color using the User Interface Brightness control in User Interface Colors preferences.
- Mute Audio
- Do one of the following:
-
To preview using RAM Preview Options, click the RAM Preview button
in the
Time Controls panel or press 0 (zero) on the numeric keypad. -
To preview using Shift+RAM Preview Options, Shift-click the RAM Preview button
in
the Time Controls panel or press Shift+0 (zero) on the numeric keypad.
Press the asterisk key (*) on the numeric
keypad during a RAM preview to place a layer marker on the selected
layers at the currently previewed frame. This is a convenient way
to place markers corresponding to important points in an audio track. -
Save a RAM preview as a movie
After Effects can save RAM previews as uncompressed AVI files (Windows) or MOV files (Mac OS). When saving a RAM preview, keep the following in mind:
-
After Effects uses the composition frame size and resolution setting to determine the final dimension in pixels of a saved RAM preview. It doesn’t consider the zoom level.
-
RAM preview doesn’t generate interlaced fields, so a saved RAM preview never contains fields.
- After you generate a RAM preview, choose Composition > Save RAM Preview.
- Type a name, specify a location, and click Save.
Loop options for previews
Click the Loop Options button in the Time Controls panel until it shows the desired state:
- Loop
- Repeatedly plays preview from beginning to end.
- Play Once
- Plays preview once.
- Ping Pong
- Repeatedly plays preview, alternating between backward and forward play.
Preview audio
When you preview audio, it’s played back in real time, unless you’ve applied Audio effects other than Stereo Mixer, in which case you may have to wait for audio to render before it plays back.
Set the sample rate for audio for the entire project in the Project Settings dialog box (File > Project Settings). CD-quality sound is 44.1 KHz, 16-bit stereo.
The Audio Hardware and Audio Output Mapping preferences determine the behavior of audio previews. These preferences do not affect final output. The quality of audio in final output is determined by the output module setting.
- To preview only audio from the current time, choose Composition > Preview > Audio Preview (Here Forward) or press the period key (.) on the numeric keypad.
- To preview only audio in the work area, choose Composition > Preview > Audio Preview (Work Area) or press Alt+period (.) (Windows) or Option+period (.) (Mac OS) on the numeric keypad.
Manually preview (scrub) video and audio
Audio panel options
During previews, the Audio panel’s 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.
- A.
- VU meter
- B.
- Level controls
- C.
- Level units
- D.
- Audio panel menu
- E.
- Level values
Choose Options on the Audio panel menu to specify the following options:
- Units
- Choose whether to display audio levels in decibels or in percentages. 100% equals 0 decibels (0 dB).
- Slider Minimum
- The minimum audio level to display in the Audio panel.
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