add flush and delay functions

audio.h

@@ -1,6 +1,8 @@
 #ifndef _AUDIO_H
 #define _AUDIO_H
 
+#include <stdint.h>
+
 typedef struct {
     void (*help)(void);
     char *name;
@@ -11,9 +13,18 @@ typedef struct {
     void (*deinit)(void);
 
     void (*start)(int sample_rate);
+    
     // block of samples
     void (*play)(short buf[], int samples);
     void (*stop)(void);
+    
+    // may be null if not implemented
+    void (*flush)(void);
+    
+    // returns the delay before the next frame to be sent to the device would actually be audible.
+    // almost certainly wrong if the buffer is empty, so put silent buffers into it to make it busy.
+    // will change dynamically, so keep watching it. Implemented in ALSA only.
+    uint32_t (*delay)();
 
     // may be NULL, in which case soft volume is applied
     void (*volume)(double vol);