Index: libs/libmythtv/videoout_xv.cpp
===================================================================
--- libs/libmythtv/videoout_xv.cpp	(revision 20500)
+++ libs/libmythtv/videoout_xv.cpp	(working copy)
@@ -67,6 +67,10 @@
 #define round(x) ((int) ((x) + 0.5))
 #endif
 
+#ifndef V_INTERLACE
+#define V_INTERLACE (0x010)
+#endif
+
 #ifndef XVMC_CHROMA_FORMAT_420
 #define XVMC_CHROMA_FORMAT_420 0x00000001
 #endif
@@ -365,6 +369,19 @@
 
     rate = (dot_clock * 1000.0) / rate;
 
+    // For an interlaced display mode, we want the refresh rate to be the field
+    // rate, so that we can use an x2 deinterlacer. It may be the case that some
+    // drivers (possibly openchrome) use false mode lines, with a doubled clock
+    // rate, so as to make the frame rate calculation produce the field rate.
+    // We check for 25 or 30 to avoid twice doubling in that case.
+    if (((mode_line.flags & V_INTERLACE) != 0) &&
+        rate > 24.5 && rate < 30.5)
+    {
+        VERBOSE(VB_GENERAL, "Doubling refresh rate for interlaced display mode");
+
+        rate *= 2;
+    }
+
     // Assume 60Hz if rate isn't good:
     if (rate < 20 || rate > 200)
     {