VideoFrame.timestamp and EncodedVideoChunk.timestamp

Fix for #809

Author: aboba

index.src.html

@@ -3693,8 +3693,10 @@
     {{VideoFrame/[[display height]]}}.
 
 : <dfn attribute for=VideoFrame>timestamp</dfn>
-:: The presentation timestamp, given in microseconds. The timestamp is copied
-    from the {{EncodedVideoChunk}} corresponding to this VideoFrame.
+:: The presentation timestamp, given in microseconds. For decode,
+    timestamp is copied from the {{EncodedVideoChunk}} corresponding
+    to this VideoFrame. For encode, timestamp is copied to the
+    {{EncodedVideoChunk}}s corresponding to this VideoFrame. 
 
     The {{VideoFrame/timestamp}} getter steps are to return
     {{VideoFrame/[[timestamp]]}}.