miniplayer流程架构

play_thread decode thread
        (usr1)>>
              fill 
        <<(usr2)prepared
loop:
    play mem1
at starting(usr1)>>
             fill
    play mem2
at starting(usr1)>>
             fill
go to loop
        <<(usr2)finished
break loop

fill:

init: flag = 0;

contex: if(flag = ~flag)

fill mem1

else

fill mem2

end if

the same goes with USR2