Move the timeline marker to the in or out point of a layer

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Move the timeline marker to the next visible keyframe

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Trim the work area to the position of the timeline marker

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Move the in or out point of a layer

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Trim the slected layers to the position of the timeline marker

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You can change which layer you have selected in the stacking order by combining the Cmd/Ctrl key with the up and down arrows

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Move the timeline marker one frame forwards or backwards

Resize and reposition a layer to match the width of the composition, whilst preserving the aspect ratio