Quick hack to fetch duration of RTMP stream using rtmpdump v2.4.

rtmp_meta.rb

require 'forwardable'

module RtmpMeta
  class Parser
    PATTERN = /duration\s+(?<duration>\d+\.?\d+)$/
    attr_reader :raw_data

    def initialize raw_data
      @raw_data = raw_data
    end

    def duration
      @duration ||= metadata[:duration]
    end

    protected

    def metadata
      @metadata ||= parse_raw_data
    end

    def parse_raw_data
      match = PATTERN.match(raw_data)
      { duration: match ? match[:duration] : '0' }
    end
  end
end

module RtmpMeta
  class MetadataCommand
    attr_reader :rtmp_url
    def initialize rtmp_url
      @rtmp_url = rtmp_url
    end

    def execute
      fetch_metadata.encode('UTF-8', invalid: :replace, replace: '?')
    end

    protected
    def fetch_metadata
      `rtmpdump -r '#{rtmp_url}' -o '/dev/null' --stop '0.01' 2>&1`
    end
  end
end

module RtmpMeta
  class Stream
    extend Forwardable
    attr_reader :metadata
    def_delegator :metadata, :duration

    def initialize stream, path
      url = [stream, path].join('/')
      @raw_data = MetadataCommand.new(url).execute
      @metadata = Parser.new(@raw_data)
    end
  end
end