diff --git a/Timeline/Audio_Track.C b/Timeline/Audio_Track.C
index 03d1d8c..6db587a 100644
--- a/Timeline/Audio_Track.C
+++ b/Timeline/Audio_Track.C
@@ -108,3 +108,36 @@ Audio_Track::handle ( int m )
             return Track::handle( m );
     }
 }
+
+
+/**********/
+/* Engine */
+/**********/
+
+/* THREAD: IO */
+/** determine region coverage and fill /buf/ with interleaved samples
+ * from /frame/ to /nframes/ for exactly /channels/ channels. */
+void
+Audio_Track::play ( sample_t *buf, nframes_t frame, nframes_t nframes, int channels )
+{
+    sample_t *cbuf = new sample_t[ nframes ];
+
+    /* quick and dirty--let the regions figure out coverage for themselves */
+    for ( list <Track_Widget *>::const_iterator i = _widgets.begin(); i != _widgets.end(); i++ )
+    {
+        const Region *r = (Region*)i;
+
+        for ( int i = channels; i-- )
+        {
+            memset( cbuf, 0, nframes * sizeof( sample_t ) );
+
+            if ( ! r->read( cbuf, frame, nframes, i ) )
+                /* error ? */;
+
+            /* interleave */
+            int k = 0;
+            for ( int j = 0; j < nframes; j += channels )
+                buf[ j ] = cbuf[ k++ ];
+        }
+    }
+}
diff --git a/Timeline/Audio_Track.H b/Timeline/Audio_Track.H
index 0b12158..0564923 100644
--- a/Timeline/Audio_Track.H
+++ b/Timeline/Audio_Track.H
@@ -53,4 +53,6 @@ public:
     void dump ( void );
     void remove_selected ( void );
 
+    void play ( sample_t *buf, nframes_t frame, nframes_t nframes, int channels );
+
 };
diff --git a/Timeline/Disk_Stream.C b/Timeline/Disk_Stream.C
index dc28c92..bd94b70 100644
--- a/Timeline/Disk_Stream.C
+++ b/Timeline/Disk_Stream.C
@@ -17,6 +17,8 @@
 /* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
 /*******************************************************************************/
 
+#include "Track_Header.H"
+
 static float seconds_to_buffer = 5.0f;
 
 /* A Disk_Stream uses a separate I/O thread to stream a track's
@@ -57,6 +59,12 @@ virtual ~Disk_Stream::Disk_Stream ( )
         jack_ringbuffer_free( _rb[ i ] );
 }
 
+Audio_Track *
+Disk_Stream::track ( void ) const
+{
+    return (Audio_Track*)_th->track();
+}
+
 /** start Disk_Stream thread */
 void
 Disk_Stream::run ( void )
@@ -77,7 +85,7 @@ Disk_Stream::io_thread ( void *arg )
 void
 Disk_Stream::read_block ( sample_t *buf )
 {
-    if ( _th->track()->play( buf, _frame, _nframes, channels() ) )
+    if ( track()->play( buf, _frame, _nframes, channels() ) )
         _frame += _nframes;
     else
         /* error */;
diff --git a/Timeline/Disk_Stream.H b/Timeline/Disk_Stream.H
index 42673a8..9813441 100644
--- a/Timeline/Disk_Stream.H
+++ b/Timeline/Disk_Stream.H
@@ -22,7 +22,10 @@
 #include <jack/ringbuffer.h>
 #include <semaphore.h>
 
-#include "Track_Header.H"
+#include <vector>
+using std::vector;
+
+class Track_Header;
 
 class Disk_Stream
 {
@@ -39,7 +42,7 @@ class Disk_Stream
 
     int channels ( void ) const { return _rb.size(); }
 
-    Track * track ( void ) const { return _th->track(); }
+    Audio_Track * track ( void ) const;
 
 protected:
 
diff --git a/Timeline/Port.H b/Timeline/Port.H
index d2288ea..6980dc8 100644
--- a/Timeline/Port.H
+++ b/Timeline/Port.H
@@ -30,6 +30,6 @@ public:
     bool connected ( void ) const { return jack_port_connected( _port ); }
     const char * name ( void ) const { return _name; }
 
-    nframes_t write ( sample_t *buf, nframes_t nframes );
+    void write ( sample_t *buf, nframes_t nframes );
 
 };