code: function fixPattern(next) {
          var pattern = config.filename || 'tn.png';
  
          if (pattern.indexOf('.') === -1) {
            pattern += '.png';
          }
  
          if (config.timemarks.length > 1 && !pattern.match(/%(s|0*i)/)) {
            var ext = path.extname(pattern);
            pattern = path.join(path.dirname(pattern), path.basename(pattern, ext) + '_%i' + ext);
          }
  
          next(null, pattern);
        }
docs: Add '_%i' to pattern when requesting multiple screenshots and no variable token is present