This demonstrates the plugin format for the FieldTrip fileio module.

example_format.m

function [varargout] = example_format(varargin)

% EXAMPLE_FORMAT demonstrates the plugin format for the FieldTrip fileio module. 
%
% Use as
%   hdr = ft_read_data('test.mff', 'headerformat', 'example_format')
%   dat = ft_read_data('test.mff', 'headerformat', 'example_format', 'dataformat', 'example_format')

st = dbstack;
if length(st)>1 && strcmp(st(2).name, 'ft_read_header')
  command = 'header';
elseif length(st)>1 && strcmp(st(2).name, 'ft_read_data')
  command = 'data';
elseif length(st)>1 && strcmp(st(2).name, 'ft_read_event')
  command = 'event';
elseif length(st)>1 && strcmp(st(2).name, 'ft_write_data')
  command = 'write';
else
  command = 'unknown';
end

nchan = 10;
fsample = 1000;
ntime = 60*fsample;

switch command
  case 'header'
    % filename = varargin{1};
    % option1 = ft_getopt(varargin(2:end), 'option1')
    % option2 = ft_getopt(varargin(2:end), 'option2')
    % etc.
    
    hdr = [];
    hdr.Fs = fsample;
    hdr.nChans = nchan;
    hdr.nTrials = 1;
    hdr.nSamples = ntime;
    hdr.nSamplesPre = 0;
    for i=1:nchan
      hdr.label{i} = num2str(i);
      hdr.chantype{i} = 'unknown';
      hdr.chanunit{i} = 'unknown';
    end
    
    % return the header
    varargout = {hdr};
    
  case 'data'
    % filename = varargin{1};
    % begsample = ft_getopt(varargin(2:end), 'begsample')
    % endsample = ft_getopt(varargin(2:end), 'endsample')
    % etc.
    
    dat = randn(nchan, ntime);
    
    % return the data
    varargout = {dat};
    
  case 'event'
    % filename = varargin{1};
    % etc.
    
    event = [];
    event.type  = 'start';
    event.value = [];
    event.sample = 1;
    event.offset = 0;
    event.duration = [];
    
    % return the event structure
    varargout = {event};
    
  case 'write'
    % write the data to file
    error('not yet implemented');
    
  otherwise
    error('it is not clear what you expect from me');
end