avfilter: add premultiply filter

Signed-off-by: Paul B Mahol <onemda@gmail.com>

Changelog

@@ -5,6 +5,7 @@ version <next>:
 - CrystalHD decoder moved to new decode API
 - add internal ebur128 library, remove external libebur128 dependency
 - Pro-MPEG CoP #3-R2 FEC protocol
+- premultiply video filter
 
 version 3.2:
 - libopenmpt demuxer

doc/filters.texi

@@ -10983,6 +10983,12 @@ Set medium thresholding (good results, default).
 @end table
 @end table
 
+@section premultiply
+Apply alpha premultiply effect to input video stream using first plane
+of second stream as alpha.
+
+Both streams must have same dimensions and same pixel format.
+
 @section prewitt
 Apply prewitt operator to input video stream.
 

libavfilter/Makefile

@@ -240,6 +240,7 @@ OBJS-$(CONFIG_PHASE_FILTER)                  += vf_phase.o
 OBJS-$(CONFIG_PIXDESCTEST_FILTER)            += vf_pixdesctest.o
 OBJS-$(CONFIG_PP_FILTER)                     += vf_pp.o
 OBJS-$(CONFIG_PP7_FILTER)                    += vf_pp7.o
+OBJS-$(CONFIG_PREMULTIPLY_FILTER)            += vf_premultiply.o framesync.o
 OBJS-$(CONFIG_PREWITT_FILTER)                += vf_convolution.o
 OBJS-$(CONFIG_PSNR_FILTER)                   += vf_psnr.o dualinput.o framesync.o
 OBJS-$(CONFIG_PULLUP_FILTER)                 += vf_pullup.o

libavfilter/allfilters.c

@@ -256,6 +256,7 @@ void avfilter_register_all(void)
     REGISTER_FILTER(PIXDESCTEST,    pixdesctest,    vf);
     REGISTER_FILTER(PP,             pp,             vf);
     REGISTER_FILTER(PP7,            pp7,            vf);
+    REGISTER_FILTER(PREMULTIPLY,    premultiply,    vf);
     REGISTER_FILTER(PREWITT,        prewitt,        vf);
     REGISTER_FILTER(PSNR,           psnr,           vf);
     REGISTER_FILTER(PULLUP,         pullup,         vf);

libavfilter/version.h

@@ -30,7 +30,7 @@
 #include "libavutil/version.h"
 
 #define LIBAVFILTER_VERSION_MAJOR   6
-#define LIBAVFILTER_VERSION_MINOR  67
+#define LIBAVFILTER_VERSION_MINOR  68
 #define LIBAVFILTER_VERSION_MICRO 100
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \