An Infinite clip appears as a dopesheet. An Infinite clip cannot be positioned, trimmed, or split because it does not have a defined size. To position, trim, split, or perform other clip manipulations on an Infinite clip, it must first be converted to an Animation clip.
To convert an Infinite clip to an Animation clip, click the Track menu icon and select Convert to Clip Track. You can also Right-click the track and select Convert to Clip Track from the context menu. The Track menu and context menu are the same.