You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: spm_file_split.m
    path of file: ./repos/bspm/thirdparty/spm12
    
    the code of the file until where you have to start completion: function Vo = spm_file_split(V, odir)
% Convert a 4D volume file into a series of 3D volume files
% FUNCTION Vo = spm_file_split(V, odir)
% V           - filename or spm_vol struct
% odir        - output directory [default: same as input]
%

    
function Vo = spm_file_split(V, odir)
% Convert a 4D volume file into a series of 3D volume files
% FUNCTION Vo = spm_file_split(V, odir)
% V           - filename or spm_vol struct
% odir        - output directory [default: same as input]
%
% Vo          - spm_vol struct array of output files
%__________________________________________________________________________
% Copyright (C) 2009 Wellcome Trust Centre for Neuroimaging

% Guillaume Flandin
% $Id: spm_file_split.m 4854 2012-08-22 13:29:10Z ged $

if ~nargin
    [V, sts] = spm_select(1,'nifti','Select a 4D volume file to split');
    if ~sts, return; end