descriptor.js

var tagToName = {
  0x03: 'ESDescriptor',
  0x04: 'DecoderConfigDescriptor',
  0x05: 'DecoderSpecificInfo',
  0x06: 'SLConfigDescriptor'
}

exports.Descriptor = {}
exports.Descriptor.decode = function (buf, start, end) {
  var tag = buf.readUInt8(start)
  var ptr = start + 1
  var lenByte
  var len = 0
  do {
    lenByte = buf.readUInt8(ptr++)
    len = (len << 7) | (lenByte & 0x7f)
  } while (lenByte & 0x80)

  var obj
  var tagName = tagToName[tag] // May be undefined; that's ok
  if (exports[tagName]) {
    obj = exports[tagName].decode(buf, ptr, end)
  } else {
    obj = {
      buffer: Buffer.from(buf.slice(ptr, ptr + len))
    }
  }

  obj.tag = tag
  obj.tagName = tagName
  obj.length = (ptr - start) + len
  obj.contentsLen = len
  return obj
}

exports.DescriptorArray = {}
exports.DescriptorArray.decode = function (buf, start, end) {
  var ptr = start
  var obj = {}
  while (ptr + 2 <= end) {
    var descriptor = exports.Descriptor.decode(buf, ptr, end)
    ptr += descriptor.length
    var tagName = tagToName[descriptor.tag] || ('Descriptor' + descriptor.tag)
    obj[tagName] = descriptor
  }
  return obj
}

exports.ESDescriptor = {}
exports.ESDescriptor.decode = function (buf, start, end) {
  var flags = buf.readUInt8(start + 2)
  var ptr = start + 3
  if (flags & 0x80) {
    ptr += 2
  }
  if (flags & 0x40) {
    var len = buf.readUInt8(ptr)
    ptr += len + 1
  }
  if (flags & 0x20) {
    ptr += 2
  }
  return exports.DescriptorArray.decode(buf, ptr, end)
}

exports.DecoderConfigDescriptor = {}
exports.DecoderConfigDescriptor.decode = function (buf, start, end) {
  var oti = buf.readUInt8(start)
  var obj = exports.DescriptorArray.decode(buf, start + 13, end)
  obj.oti = oti
  return obj
}