avfilter: add palettegen filter

doc/filters.texi

@@ -6927,6 +6927,30 @@ pad="2*iw:2*ih:ow-iw:oh-ih"
 @end example
 @end itemize
 
+@section palettegen
+
+Generate one palette for a whole video stream.
+
+It accepts the following option:
+
+@table @option
+@item reserve_transparent
+Create a palette of 255 colors maximum and reserve the last one for
+transparency. Reserving the transparency color is useful for GIF optimization.
+If not set, the maximum of colors in the palette will be 256.
+Set by default.
+@end table
+
+@subsection Examples
+
+@itemize
+@item
+Generate a representative palette of a given video using @command{ffmpeg}:
+@example
+ffmpeg -i input.mkv -vf palettegen palette.png
+@end example
+@end itemize
+
 @section perspective
 
 Correct perspective of video not recorded perpendicular to the screen.

libavfilter/Makefile

@@ -160,6 +160,7 @@ OBJS-$(CONFIG_OPENCL)                        += deshake_opencl.o unsharp_opencl.
 OBJS-$(CONFIG_OVERLAY_FILTER)                += vf_overlay.o dualinput.o framesync.o
 OBJS-$(CONFIG_OWDENOISE_FILTER)              += vf_owdenoise.o
 OBJS-$(CONFIG_PAD_FILTER)                    += vf_pad.o
+OBJS-$(CONFIG_PALETTEGEN_FILTER)             += vf_palettegen.o
 OBJS-$(CONFIG_PERMS_FILTER)                  += f_perms.o
 OBJS-$(CONFIG_PERSPECTIVE_FILTER)            += vf_perspective.o
 OBJS-$(CONFIG_PHASE_FILTER)                  += vf_phase.o

libavfilter/allfilters.c

@@ -175,6 +175,7 @@ void avfilter_register_all(void)
     REGISTER_FILTER(OVERLAY,        overlay,        vf);
     REGISTER_FILTER(OWDENOISE,      owdenoise,      vf);
     REGISTER_FILTER(PAD,            pad,            vf);
+    REGISTER_FILTER(PALETTEGEN,     palettegen,     vf);
     REGISTER_FILTER(PERMS,          perms,          vf);
     REGISTER_FILTER(PERSPECTIVE,    perspective,    vf);
     REGISTER_FILTER(PHASE,          phase,          vf);