anchor.diff:  	(rcursor rec) (chunk-queue rec)
   	(wcursor rec) (cdr (chunk-queue rec))))
   
  +(defgeneric stream-playback-start (stream-record))
  +
  +(defgeneric stream-playback-stop (stream-record))
  +
   (defmethod stream-playback-start ((rec stream-record))
     (bt:acquire-lock (vacancy-lock (car (rcursor rec)))))
   
  
positive.code:   (bt:release-lock (vacancy-lock (car (rcursor rec)))))
  
  (defclass video-stream-record (stream-record)
    (frame-delay :accessor frame-delay :initarg :frame-delay))
  
  (defclass av-container ()
    ((filename :accessor filename :initarg :filename :initform nil)
  
negative.code:    (wcursor :accessor wcursor)
     (final :accessor final :initform nil)
     (buffer :accessor buffer :type '(unsigned-byte 8))
     (frame-delay :accessor frame-delay :initarg :frame-delay)
     (container :accessor container :initarg :container)))
  
  (defmethod initialize-ring ((rec stream-record) ring-length frame-size element-type)
  