diff --git a/include/media/nbaio/MonoPipeReader.h b/include/media/nbaio/MonoPipeReader.h
index 0e1c992..78fe867 100644
--- a/include/media/nbaio/MonoPipeReader.h
+++ b/include/media/nbaio/MonoPipeReader.h
@@ -49,6 +49,8 @@
 
     virtual ssize_t read(void *buffer, size_t count, int64_t readPTS);
 
+    virtual void    onTimestamp(const AudioTimestamp& timestamp);
+
     // NBAIO_Source end
 
 #if 0   // until necessary
diff --git a/include/media/nbaio/NBAIO.h b/include/media/nbaio/NBAIO.h
index cc5b3e6..1da0c73 100644
--- a/include/media/nbaio/NBAIO.h
+++ b/include/media/nbaio/NBAIO.h
@@ -306,6 +306,10 @@
     virtual ssize_t readVia(readVia_t via, size_t total, void *user,
                             int64_t readPTS, size_t block = 0);
 
+    // Invoked asynchronously by corresponding sink when a new timestamp is available.
+    // Default implementation ignores the timestamp.
+    virtual void    onTimestamp(const AudioTimestamp& timestamp) { }
+
 protected:
     NBAIO_Source(NBAIO_Format format = Format_Invalid) : NBAIO_Port(format), mFramesRead(0) { }
     virtual ~NBAIO_Source() { }