play.cr

require "json"

class Base
  def create_json
    io = IO::Memory.new
    b = JSON::Builder.new(io)
    b.start_document
    b.start_object
    self.to_json(b)
    b.end_object
    b.end_document
    io.to_s
  end
  
  def to_json(builder)
    builder.scalar nil
  end
  
end

class Ext < Base
  def to_json(builder)
    builder.field "audio" do
      builder.object do
      	builder.field "num_channels", "1"
    	end
    end
    builder.field "base" do
    	super(builder)
    end
    
        # avoid nil values by converting nil=0
    builder.field "direction", "Incoming"
    builder.field "encryption", "no"
    builder.field "bytes", 1324
    builder.field "channel_rate", 3
    builder.field "drop", 4
    builder.field "jitter", 3
    builder.field "last_interval_lost", 2
    builder.field "last_interval_received", 1
    builder.field "loss", 5
    builder.field "max_jitter", 5
	end
end

x = Ext.new.create_json
p x.to_s