doc/encoders: Add doc for av1_qsv

Add doc for av1_qsv.

Signed-off-by: Wenbin Chen <wenbin.chen@intel.com>

doc/encoders.texi

@@ -3775,6 +3775,38 @@ Number of columns for tiled encoding (requires libmfx >= 1.29).
 Number of rows for tiled encoding (requires libmfx  >= 1.29).
 @end table
 
+@subsection AV1 Options
+These options are used by av1_qsv (requires libvpl).
+@table @option
+@item @var{profile}
+@table @samp
+@item unknown
+@item main
+@end table
+
+@item @var{tile_cols}
+Number of columns for tiled encoding.
+
+@item @var{tile_rows}
+Number of rows for tiled encoding.
+
+@item @var{adaptive_i}
+This flag controls insertion of I frames by the QSV encoder. Turn ON this flag
+to allow changing of frame type from P and B to I.
+
+@item @var{adaptive_b}
+This flag controls changing of frame type from B to P.
+
+@item @var{b_strategy}
+This option controls usage of B frames as reference.
+
+@item @var{extbrc}
+Extended bitrate control.
+
+@item @var{look_ahead_depth}
+Depth of look ahead in number frames, available when extbrc option is enabled.
+@end table
+
 @section snow
 
 @subsection Options