samer@0: function [Sched,GetData]=playaudio_unfold(buflen,unfold_fn,S,Snk,varargin)
samer@0: % playaudio_async - Play stream of audio data asynchronously
samer@0: %
samer@0: % playaudio :: 
samer@0: %    N:natural      ~'buflen',
samer@0: %    (S->[[C,N]],S) ~'unfolding function',
samer@36: %    sink(C,R)      ~'sink for C channels',
samer@0: %    options {
samer@0: %       maxbuf  :: natural/2*max(size(X))   ~'maximum buffer size';
samer@0: %       hook    :: (iterator(S)->iterator(T)) ~'fn to build iterator';
samer@0: %       onstart :: A -> action      ~'called BEFORE timer starts';
samer@0: %       onstop  :: A -> action      ~'called AFTER timer stops';
samer@0: %       onfinish:: A -> action      ~'called when end of signal reached';
samer@0: %       defer   :: bool / 0         ~'if 1, don't start the timer'
samer@0: %    }
samer@0: % -> sched(S) ~'scheduler api functions',
samer@0: %    (S -> [[N]]) ~'function to recover audio from iterator state'.
samer@0: %
samer@0: % iterator(S) ::= cell {(S->action S)~'state transformer', S~'initial state'}.
samer@0: %
samer@0: % sched(S) ::= struct {
samer@0: %		dispose   :: unit -> action unit;
samer@0: %		isrunning :: unit -> action bool;
samer@0: %		startat	 :: real -> action unit;
samer@0: %		start		 :: unit -> action unit;
samer@0: %		stop		 :: unit -> action unit;
samer@0: %		rewind	 :: unit -> action unit;
samer@0: %		getstate	 :: unit -> action S;
samer@0: %		setstate	 :: S    -> action unit
samer@0: % }.
samer@0: %
samer@0: % The 'hook' option gives the caller an opportunity to elaborate on the
samer@0: % 'iterator' used to drive the audio playback. The 'iterator' is a cell
samer@0: % array contain a state transformer function and initial state. The caller
samer@0: % can use this to build a more complex iterator the does other things
samer@0: % for each buffer of samples.
samer@0: %
samer@0: % The third return value is a function which can be used in a state
samer@0: % transformer function to recover a buffer of audio samples from the
samer@0: % current state.
samer@0: %
samer@0: % NB: all the audio buffers must be the same size for this to work.
samer@0: % NB: the rewind function should only be called when the timer is stopped.
samer@0: 
samer@0: 	N=buflen;
samer@37: 	opts=options('onstop',@nop,'onstart',@nop,'onfinish',@nop, ...
samer@0: 		'period_adjust',0.9,'preload',2,'sched',@iterate_timed,varargin{:});
samer@0: 
samer@0: 	it=feval(getparam(opts,'hook',@id),{@playbuf,S});
samer@0: 
samer@0: 	maxbuf=getparam(opts,'maxbuf',2*N);
samer@0: 	sync_delta=getparam(opts,'sync_delta',0.02);
samer@0: 	sync_offset=getparam(opts,'sync_offset',0);
samer@0: 
samer@0: 	L=construct(Snk);
samer@0: 	write=L.writer(maxbuf);
samer@0: 	period=(N/rate(Snk))*opts.period_adjust;
samer@0: 
samer@0: 	Sched=opts.sched(it{1},it{2},period, ...
samer@0: 		'exec_mode','fixedRate', 'busy_mode','drop', opts, ...
samer@0: 		'onstart',@onstart,'onstop',@onstop); 
samer@0: 	getstate=Sched.getstate;
samer@0: 	odispose=Sched.dispose;
samer@0: 	Sched.atend=@()isempty(getstate());
samer@0: 	Sched.dispose=@dispose;
samer@0: 	Sched.setGain=L.setGain;
samer@0: 
samer@0: 	GetData=@head;
samer@0: 
samer@0: 	function dispose
samer@0: 		odispose();
samer@0: 		L.dispose();
samer@0: 	end
samer@0: 
samer@0: 	function onstart(S),
samer@0: 		opts.onstart(S);
samer@0: 		L.start();
samer@0: 		for i=1:opts.preload
samer@0: 			write(zeros(maxbuf,1));
samer@0: 		end
samer@0: 	end
samer@0: 
samer@0: 	function onstop(S),
samer@0: 		write(zeros(maxbuf,1));
samer@0: 		L.stop();
samer@0: 		opts.onstop(S);
samer@0: 	end
samer@0: 
samer@0: 	function S=playbuf(S)
samer@0: 		[y,S]=unfold_fn(S);
samer@0: 		n=size(y,2);
samer@0: 		if n>0, write(y); end
samer@0: 	end
samer@0: end
samer@0: