avfilter: add paletteuse filter

doc/filters.texi

@@ -6909,6 +6909,7 @@ pad="2*iw:2*ih:ow-iw:oh-ih"
 @end example
 @end itemize
 
+@anchor{palettegen}
 @section palettegen
 
 Generate one palette for a whole video stream.
@@ -6954,6 +6955,55 @@ ffmpeg -i input.mkv -vf palettegen palette.png
 @end example
 @end itemize
 
+@section paletteuse
+
+Use a palette to downsample an input video stream.
+
+The filter takes two inputs: one video stream and a palette. The palette must
+be a 256 pixels image.
+
+It accepts the following options:
+
+@table @option
+@item dither
+Select dithering mode. Available algorithms are:
+@table @samp
+@item bayer
+Ordered 8x8 bayer dithering (deterministic)
+@item heckbert
+Dithering as defined by Paul Heckbert in 1982 (simple error diffusion).
+Note: this dithering is sometimes considered "wrong" and is included as a
+reference.
+@item floyd_steinberg
+Floyd and Steingberg dithering (error diffusion)
+@item sierra2
+Frankie Sierra dithering v2 (error diffusion)
+@item sierra2_4a
+Frankie Sierra dithering v2 "Lite" (error diffusion)
+@end table
+
+Default is @var{sierra2_4a}.
+
+@item bayer_scale
+When @var{bayer} dithering is selected, this option defines the scale of the
+pattern (how much the crosshatch pattern is visible). A low value means more
+visible pattern for less banding, and higher value means less visible pattern
+at the cost of more banding.
+
+The option must be an integer value in the range [0,5]. Default is @var{2}.
+@end table
+
+@subsection Examples
+
+@itemize
+@item
+Use a palette (generated for example with @ref{palettegen}) to encode a GIF
+using @command{ffmpeg}:
+@example
+ffmpeg -i input.mkv -i palette.png -lavfi paletteuse output.gif
+@end example
+@end itemize
+
 @section perspective
 
 Correct perspective of video not recorded perpendicular to the screen.

libavfilter/Makefile

@@ -161,6 +161,7 @@ OBJS-$(CONFIG_OVERLAY_FILTER)                += vf_overlay.o dualinput.o framesy
 OBJS-$(CONFIG_OWDENOISE_FILTER)              += vf_owdenoise.o
 OBJS-$(CONFIG_PAD_FILTER)                    += vf_pad.o
 OBJS-$(CONFIG_PALETTEGEN_FILTER)             += vf_palettegen.o
+OBJS-$(CONFIG_PALETTEUSE_FILTER)             += vf_paletteuse.o dualinput.o framesync.o
 OBJS-$(CONFIG_PERMS_FILTER)                  += f_perms.o
 OBJS-$(CONFIG_PERSPECTIVE_FILTER)            += vf_perspective.o
 OBJS-$(CONFIG_PHASE_FILTER)                  += vf_phase.o

libavfilter/allfilters.c

@@ -176,6 +176,7 @@ void avfilter_register_all(void)
     REGISTER_FILTER(OWDENOISE,      owdenoise,      vf);
     REGISTER_FILTER(PAD,            pad,            vf);
     REGISTER_FILTER(PALETTEGEN,     palettegen,     vf);
+    REGISTER_FILTER(PALETTEUSE,     paletteuse,     vf);
     REGISTER_FILTER(PERMS,          perms,          vf);
     REGISTER_FILTER(PERSPECTIVE,    perspective,    vf);
     REGISTER_FILTER(PHASE,          phase,          vf);