[xiph-commits] r16484 - trunk/theora/lib

[xiphmont at svn.xiph.org]

Author: xiphmont
Date: 2009-08-18 15:39:28 -0700 (Tue, 18 Aug 2009)
New Revision: 16484

Modified:
   trunk/theora/lib/rate.c
Log:
The code in select_qi that looks for budget underflow and
force-reduces the log_qtarget was predicated on "if drop frames are
enabled and not infinite-buffer two pass mode".  This was primarily
driven by use cases at the time and is subtly inappropriate.

Modify the predication to 'if we don't have a minimum quality level';
this allows proper behavior in the case where we have a minimum
quality level but aren't using 'soft-target'.  Otherwise, lambda could
still drop to min when we were trying to force a minimum qi, which
results in what look like 'waterfalls' as SKIP triggers on large
number of blocks but the quantizer is still very fine.



Modified: trunk/theora/lib/rate.c
===================================================================
--- trunk/theora/lib/rate.c	2009-08-18 21:56:31 UTC (rev 16483)
+++ trunk/theora/lib/rate.c	2009-08-18 22:39:28 UTC (rev 16484)
@@ -672,7 +672,11 @@
      next buf_delay frames.
     However, we could bust the budget on the very next frame, so check for that
      here, if we're not using a soft target.*/
-  if(!_enc->rc.cap_underflow||_enc->rc.drop_frames){
+  /* Disabled when our minimum qi > 0; if we saturate log_qtarget to
+     to the maximum possible size when we have a minimum qi, the
+     resulting lambda will interact very strangely with SKIP.  The
+     resulting artifacts look like waterfalls. */
+  if(_enc->state.info.quality==0){
     ogg_int64_t log_hard_limit;
     /*Compute the maximum number of bits we can use in the next frame.
       Allow 50% of the rate for a single frame for prediction error.
@@ -704,6 +708,8 @@
   ogg_int64_t log_scale;
   int         dropped;
   dropped=0;
+  /* Drop frames also disabled for now in the case of infinite-buffer
+     two-pass mode */
   if(!_enc->rc.drop_frames||_enc->rc.twopass&&_enc->rc.frame_metrics==NULL){
     _droppable=0;
   }