Fix memory layout of NV12 image example

According to the text:
- The coded width and coded height must be even. So image cannot be 16x9. This
update makes it 16x10
- There should be one Y byte per pixel, so 16x10 Y bytes (example only had 14
bytes per row)
- The U and V components are sub-sampled horizontally and vertically by a factor
of 2, and interleaved, so there should 16x10/4 = 40 UV blocks (example only
sub-sampled horizontally).

This update also fixes occurrences of "horizontaly".

Author: tidoust

index.src.html

@@ -4268,7 +4268,7 @@
     planes of Chroma, denoted Y, U and V, and present in this order. It is also
     often refered to as Planar YUV 4:2:0.
 
-    The U an V planes are [=sub-sampled=] horizontaly and vertically by a
+    The U an V planes are [=sub-sampled=] horizontally and vertically by a
     [=factor=] of 2 compared to the Y plane.
 
     Each sample in this format is 8 bits.
@@ -4296,7 +4296,7 @@
     present in this order. It is also often refered to as Planar YUV 4:2:0 with
     an alpha channel.
 
-    The U an V planes are [=sub-sampled=] horizontaly and vertically by a
+    The U an V planes are [=sub-sampled=] horizontally and vertically by a
     [=factor=] of 2 compared to the Y and Alpha planes.
 
     Each sample in this format is 8 bits.
@@ -4325,7 +4325,7 @@
     planes of Chroma, denoted Y, U and V, and present in this order. It is also
     often refered to as Planar YUV 4:2:2.
 
-    The U an V planes are [=sub-sampled=] horizontaly by a [=factor=] of 2
+    The U an V planes are [=sub-sampled=] horizontally by a [=factor=] of 2
     compared to the Y plane, and not [=sub-sampled=] vertically.
 
     Each sample in this format is 8 bits.
@@ -4366,7 +4366,7 @@
     another plane for the two Chroma components. The two planes are present in
     this order, and are refered to as respectively the Y plane and the UV plane.
 
-    The U an V components are [=sub-sampled=] horizontaly and vertically by a
+    The U an V components are [=sub-sampled=] horizontally and vertically by a
     [=factor=] of 2 compared to the components in the Y planes.
 
     Each sample in this format is 8 bits.
@@ -4389,28 +4389,25 @@
     {{VideoFrame/visibleRect}}.{{DOMRectInit/y}}) MUST be even.
 
     <div class=example>
-    An image in the NV12 pixel format that is 16 pixels wide and 9 pixels tall
+    An image in the NV12 pixel format that is 16 pixels wide and 10 pixels tall
     will be arranged like so in memory:
 
     ```
-        YYYYYYYYYYYYYY
-        YYYYYYYYYYYYYY
-        YYYYYYYYYYYYYY
-        YYYYYYYYYYYYYY
-        YYYYYYYYYYYYYY
-        YYYYYYYYYYYYYY
-        YYYYYYYYYYYYYY
-        YYYYYYYYYYYYYY
-        YYYYYYYYYYYYYY
-        UVUVUVUVUVUVUV
-        UVUVUVUVUVUVUV
-        UVUVUVUVUVUVUV
-        UVUVUVUVUVUVUV
-        UVUVUVUVUVUVUV
-        UVUVUVUVUVUVUV
-        UVUVUVUVUVUVUV
-        UVUVUVUVUVUVUV
-        UVUVUVUVUVUVUV
+        YYYYYYYYYYYYYYYY
+        YYYYYYYYYYYYYYYY
+        YYYYYYYYYYYYYYYY
+        YYYYYYYYYYYYYYYY
+        YYYYYYYYYYYYYYYY
+        YYYYYYYYYYYYYYYY
+        YYYYYYYYYYYYYYYY
+        YYYYYYYYYYYYYYYY
+        YYYYYYYYYYYYYYYY
+        YYYYYYYYYYYYYYYY
+        UVUVUVUVUVUVUVUV
+        UVUVUVUVUVUVUVUV
+        UVUVUVUVUVUVUVUV
+        UVUVUVUVUVUVUVUV
+        UVUVUVUVUVUVUVUV
     ```
 
     All samples being linear in memory.