Yeah, so it means mini-batches of 3-channel RGB clips. The batch size is the 5th dimension. 3 is the number of channels which is the 4th dimension. T denotes the number of frames → 3rd dimension and spatial size of the frame are the last two dimensions.
For e.g. 16, 3, 16, 112, 112 → Here 16 is batch size. This should be the input to your 3D model.