Скачать или смотреть Adjust volume over time

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To create a more nuanced sound mix, change the volume over time using keyframes. Keyframes are special marks that contain settings — in this case, the audio volume.
What you learned: Add audio keyframes
Check the Timeline panel Settings menu to make sure Show Audio Keyframes is enabled. You may need to increase the height of the audio track to see keyframes on audio clips.
Choose the Pen tool.
To add a new keyframe mark, click the thin white line on an audio clip.
Drag the keyframe up to make the sound louder, or drag it down to make it quieter.
Drag the keyframe left or right to apply the setting earlier or later.
To delete a keyframe, select it and press Backspace (Windows) or Delete (macOS).
With the Pen tool, you can lasso to select multiple keyframes and then move or delete them together. These kinds of keyframes are added to clips, not to tracks (it’s also possible to add keyframes to tracks).
Choose the Selection tool when you have finished working with keyframes.