How to set the selected item in a radio button group in handlebars template?

Question

In a handlebars template, how do you set a radio button group to the right value using only the template? Can this be done directly in the template?

For an example,

Answer 1

I really liked the answer from ChrisV, once I understood it. I really struggled to get there from here. Please consider this a supporting comment to the answers above. I will say my use case was a tiny bit different. I'm using Express and I wanted to set the checkbox from a route. It wasn't totally clear to me how to call the helper function. Obviously, I'm using two different radio button groupings.

In app.js, where I initially setup the view engine

var hbs = require('hbs');
hbs.registerPartials(__dirname + '/views/partials');
hbs.registerHelper('checked', function (value, test) {
  if (value == undefined) return '';
  return value == test ? 'checked' : '';
});
app.set('view engine', 'hbs');

I set the route in index.js

var express = require('express');
var router = express.Router();
router.get('/display_form', function (req, res, next) {
//... play with data.  use req.query.optionsRadiosA, etc...
//  var outputA = "video"
    res.render('formpage', {
        title: 'Setup Page',
        optionsRadiosA: outputA,    // use variable
        optionsRadiosB: 'Audio'     // or use string
    });
});

and finally, my template, formpage.hbs (extract shown...)

{{title}}

    
Channel A Setup
           
    
          Video
    
    
         Audio
    
    
Channel B Setup
    
         Video
    
    
          Audio