avfilter/dctdnoiz: add 8x8 dct and make it the default

8x8 is about 5x faster than 16x16 on 1080p input. Since a block size of
8x8 makes the filter almost usable (time wise) and it's not obvious if
8x8 or 16x16 is better from a quality PoV (it really depends on the
input and parameters), the filter now defaults to 8x8, and as a result
libavfilter is micro bumped.

1 files changed, 19 insertions, 5 deletions

diff --git a/doc/filters.texi b/doc/filters.texi
index 86feebccdc..f59926a05e 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -3219,7 +3219,7 @@ curves=psfile='MyCurvesPresets/purple.asv':green='0.45/0.53'
 
 Denoise frames using 2D DCT (frequency domain filtering).
 
-This filter is not designed for real time and can be extremely slow.
+This filter is not designed for real time.
 
 The filter accepts the following options:
 
@@ -3235,14 +3235,14 @@ If you need a more advanced filtering, see @option{expr}.
 Default is @code{0}.
 
 @item overlap
-Set number overlapping pixels for each block. Each block is of size
-@code{16x16}. Since the filter can be slow, you may want to reduce this value,
-at the cost of a less effective filter and the risk of various artefacts.
+Set number overlapping pixels for each block. Since the filter can be slow, you
+may want to reduce this value, at the cost of a less effective filter and the
+risk of various artefacts.
 
 If the overlapping value doesn't allow to process the whole input width or
 height, a warning will be displayed and according borders won't be denoised.
 
-Default value is @code{15}.
+Default value is @var{blocksize}-1, which is the best possible setting.
 
 @item expr, e
 Set the coefficient factor expression.
@@ -3254,6 +3254,15 @@ If this is option is set, the @option{sigma} option will be ignored.
 
 The absolute value of the coefficient can be accessed through the @var{c}
 variable.
+
+@item n
+Set the @var{blocksize} using the number of bits. @code{1<<@var{n}} defines the
+@var{blocksize}, which is the width and height of the processed blocks.
+
+The default value is @var{3} (8x8) and can be raised to @var{4} for a
+@var{blocksize} of 16x16. Note that changing this setting has huge consequences
+on the speed processing. Also, a larger block size does not necessarily means a
+better de-noising.
 @end table
 
 @subsection Examples
@@ -3268,6 +3277,11 @@ The same operation can be achieved using the expression system:
 dctdnoiz=e='gte(c, 4.5*3)'
 @end example
 
+Violent denoise using a block size of @code{16x16}:
+@example
+dctdnoiz=15:n=4
+@end example
+
 @anchor{decimate}
 @section decimate