lavc/qsvenc: use VBR if maxrate is not specified on Windows

Currently AVBR is disabled and VBR is the default method if maxrate is
not specified on Linux, but AVBR is the default one if maxrate is not
specified on Windows. In order to make user experience better accross
Linux and Windows, use VBR by default on Windows if maxrate is not
specified. User need to set both avbr_accuracy and avbr_convergence to
non-zero explicitly and not to specify maxrate if AVBR is expected.

In addition, AVBR works for H264 and HEVC only in the SDK.

$ ffmpeg.exe -v verbose -f lavfi -i yuvtestsrc -vf "format=nv12" -c:v
vp9_qsv -f null -

1 files changed, 29 insertions, 16 deletions

diff --git a/doc/encoders.texi b/doc/encoders.texi
index d36464d629..d2046e437d 100644
--- a/doc/encoders.texi
+++ b/doc/encoders.texi
@@ -3244,9 +3244,9 @@ the average bitrate.
 than the average bitrate.
 
 @item
-@var{AVBR} - average VBR mode, when @option{maxrate} is not specified. This mode
-is further configured by the @option{avbr_accuracy} and
-@option{avbr_convergence} options.
+@var{AVBR} - average VBR mode, when @option{maxrate} is not specified, both
+@option{avbr_accuracy} and @option{avbr_convergence} are set to non-zero. This
+mode is available for H264 and HEVC on Windows.
 @end itemize
 @end itemize
 
@@ -3300,19 +3300,6 @@ Specifies how many asynchronous operations an application performs
 before the application explicitly synchronizes the result. If zero,
 the value is not specified.
 
-@item @var{avbr_accuracy}
-Accuracy of the AVBR ratecontrol (unit of tenth of percent).
-
-@item @var{avbr_convergence}
-Convergence of the AVBR ratecontrol (unit of 100 frames)
-
-The parameters @var{avbr_accuracy} and @var{avbr_convergence} are for the
-average variable bitrate control (AVBR) algorithm.
-The algorithm focuses on overall encoding quality while meeting the specified
-bitrate, @var{target_bitrate}, within the accuracy range @var{avbr_accuracy},
-after a @var{avbr_Convergence} period. This method does not follow HRD and the
-instant bitrate is not capped or padded.
-
 @item @var{preset}
 This option itemizes a range of choices from veryfast (best speed) to veryslow
 (best quality).
@@ -3518,6 +3505,19 @@ Provides a hint to encoder about the scenario for the encoding session.
 @item remotegaming
 @end table
 
+@item @var{avbr_accuracy}
+Accuracy of the AVBR ratecontrol (unit of tenth of percent).
+
+@item @var{avbr_convergence}
+Convergence of the AVBR ratecontrol (unit of 100 frames)
+
+The parameters @var{avbr_accuracy} and @var{avbr_convergence} are for the
+average variable bitrate control (AVBR) algorithm.
+The algorithm focuses on overall encoding quality while meeting the specified
+bitrate, @var{target_bitrate}, within the accuracy range @var{avbr_accuracy},
+after a @var{avbr_Convergence} period. This method does not follow HRD and the
+instant bitrate is not capped or padded.
+
 @end table
 
 @subsection HEVC Options
@@ -3681,6 +3681,19 @@ Provides a hint to encoder about the scenario for the encoding session.
 @item remotegaming
 @end table
 
+@item @var{avbr_accuracy}
+Accuracy of the AVBR ratecontrol (unit of tenth of percent).
+
+@item @var{avbr_convergence}
+Convergence of the AVBR ratecontrol (unit of 100 frames)
+
+The parameters @var{avbr_accuracy} and @var{avbr_convergence} are for the
+average variable bitrate control (AVBR) algorithm.
+The algorithm focuses on overall encoding quality while meeting the specified
+bitrate, @var{target_bitrate}, within the accuracy range @var{avbr_accuracy},
+after a @var{avbr_Convergence} period. This method does not follow HRD and the
+instant bitrate is not capped or padded.
+
 @end table
 
 @subsection MPEG2 Options