Merge remote-tracking branch 'qatar/master'

* qatar/master:
  proresenc: alpha coding support
Merged-by: Michael Niedermayer <michaelni@gmx.at>

doc/encoders.texi

@@ -836,6 +836,7 @@ Select the ProRes profile to encode
 @item lt
 @item standard
 @item hq
+@item 4444
 @end table
 
 @item quant_mat @var{integer}
@@ -865,6 +866,11 @@ Override the 4-byte vendor ID.
 A custom vendor ID like @var{apl0} would claim the stream was produced by
 the Apple encoder.
 
+@item alpha_bits @var{integer}
+Specify number of bits for alpha component.
+Possible values are @var{0}, @var{8} and @var{16}.
+Use @var{0} to disable alpha plane coding.
+
 @end table
 
 @subsection Speed considerations