Fix grammar / clarify documentation for the format and noformat

filters.

Originally committed as revision 20440 to svn://svn.ffmpeg.org/ffmpeg/trunk

doc/libavfilter.texi

@@ -114,11 +114,11 @@ The default value of ``width'' and ``height'' is 0.
 @section format
 
 Convert the input video to one of the specified pixel formats.
-Libavfilter will try to pick one that is supported as the input to
+Libavfilter will try to pick one that is supported for the input to
 the next filter.
 
-The filter takes as argument a list of pixel format names, separated
-by ``:'', for example ``yuv420p:monow:rgb24''.
+The filter accepts a list of pixel format names, separated by ``:'',
+for example ``yuv420p:monow:rgb24''.
 
 The following command:
 
@@ -130,11 +130,11 @@ will convert the input video to the format ``yuv420p''.
 
 @section noformat
 
-Force libavfilter not to use any of the specified pixel formats as the
+Force libavfilter not to use any of the specified pixel formats for the
 input to the next filter.
 
-The filter takes as argument a list of pixel format names, separated
-by ``:'', for example ``yuv420p:monow:rgb24''.
+The filter accepts a list of pixel format names, separated by ``:'',
+for example ``yuv420p:monow:rgb24''.
 
 The following command:
 
@@ -142,7 +142,7 @@ The following command:
 ./ffmpeg -i in.avi -vfilters "noformat=yuv420p, vflip" out.avi
 @end example
 
-will make libavfilter use a format different from ``yuv420p'' as the
+will make libavfilter use a format different from ``yuv420p'' for the
 input to the vflip filter.
 
 @section null