function identifyStream (name, cb) {
  var first = true
  return through2(function (chunk, enc, cb2) {
    if (first) {
      first = false
      cb(identify(name, chunk))
    }
    this.push(chunk)
    cb2()
  })
}
@param {string} name
@param {function(string): any} cb
@returns {Transform}