multipelx id as meta

gistfile1.txt

var concat = require('concat-stream')
var plex1 = require('multiplex')

var meta = {id:'mystream', collect:true}
var s = plex1.createStream(JSON.stringify(meta))

var plex2 = multiplex(function onStream(stream, meta) {
  var m = JSON.parse(stream.meta)
  if (m.collect) return stream.pipe(collect(m))
  // do something else
})

plex1.pipe(plex2)

fs.createReadStream('file.ext').pipe(s)

function collect(meta) {
  return concat(function(data) {
   self.emit('data', meta, data)
  })
}