diff --git a/gfx/ycbcr/yuv_convert.cpp b/gfx/ycbcr/yuv_convert.cpp
--- a/gfx/ycbcr/yuv_convert.cpp
+++ b/gfx/ycbcr/yuv_convert.cpp
@@ -26,16 +26,32 @@ namespace mozilla {
 
 namespace gfx {
  
 // 16.16 fixed point arithmetic
 const int kFractionBits = 16;
 const int kFractionMax = 1 << kFractionBits;
 const int kFractionMask = ((1 << kFractionBits) - 1);
 
+NS_GFX_(YUVType) TypeFromSize(int ywidth, 
+                              int yheight, 
+                              int cbcrwidth, 
+                              int cbcrheight)
+{
+  if (ywidth == cbcrwidth && yheight == cbcrheight) {
+    return YV24;
+  }
+  else if (ywidth / 2 == cbcrwidth && yheight == cbcrheight) {
+    return YV16;
+  }
+  else {
+    return YV12;
+  }
+}
+
 // Convert a frame of YUV to 32 bit ARGB.
 NS_GFX_(void) ConvertYCbCrToRGB32(const uint8* y_buf,
                                   const uint8* u_buf,
                                   const uint8* v_buf,
                                   uint8* rgb_buf,
                                   int pic_x,
                                   int pic_y,
                                   int pic_width,
diff --git a/gfx/ycbcr/yuv_convert.h b/gfx/ycbcr/yuv_convert.h
--- a/gfx/ycbcr/yuv_convert.h
+++ b/gfx/ycbcr/yuv_convert.h
@@ -36,16 +36,18 @@ enum Rotate {
 // Filter affects how scaling looks.
 enum ScaleFilter {
   FILTER_NONE = 0,        // No filter (point sampled).
   FILTER_BILINEAR_H = 1,  // Bilinear horizontal filter.
   FILTER_BILINEAR_V = 2,  // Bilinear vertical filter.
   FILTER_BILINEAR = 3     // Bilinear filter.
 };
 
+NS_GFX_(YUVType) TypeFromSize(int ywidth, int yheight, int cbcrwidth, int cbcrheight);
+
 // Convert a frame of YUV to 32 bit ARGB.
 // Pass in YV16/YV12 depending on source format
 NS_GFX_(void) ConvertYCbCrToRGB32(const uint8* yplane,
                                   const uint8* uplane,
                                   const uint8* vplane,
                                   uint8* rgbframe,
                                   int pic_x,
                                   int pic_y,