avfilter: add signalstats filter

Signed-off-by: Mark Heath <silicontrip@gmail.com>
Signed-off-by: Dave Rice <dave@dericed.com>
Signed-off-by: Clément Bœsch <u@pkh.me>

6 files changed, 648 insertions, 1 deletions

diff --git a/Changelog b/Changelog
index 56a5ddf485..fa443dc22d 100644
--- a/Changelog
+++ b/Changelog
@@ -28,6 +28,7 @@ version <next>:
 - WebVTT encoder
 - showcqt multimedia filter
 - zoompan filter
+- signalstats filter
 
 
 version 2.2:
diff --git a/doc/filters.texi b/doc/filters.texi
index d8ed7f74ca..157adcda7b 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -7532,6 +7532,172 @@ Swap the second and third planes of the input:
 ffmpeg -i INPUT -vf shuffleplanes=0:2:1:3 OUTPUT
 @end example
 
+@section signalstats
+Evaluate various visual metrics that assist in determining issues associated
+with the digitization of analog video media.
+
+By default the filter will log these metadata values:
+
+@table @option
+@item YMIN
+Display the minimal Y value contained within the input frame. Expressed in
+range of [0-255].
+
+@item YLOW
+Display the Y value at the 10% percentile within the input frame. Expressed in
+range of [0-255].
+
+@item YAVG
+Display the average Y value within the input frame. Expressed in range of
+[0-255].
+
+@item YHIGH
+Display the Y value at the 90% percentile within the input frame. Expressed in
+range of [0-255].
+
+@item YMAX
+Display the maximum Y value contained within the input frame. Expressed in
+range of [0-255].
+
+@item UMIN
+Display the minimal U value contained within the input frame. Expressed in
+range of [0-255].
+
+@item ULOW
+Display the U value at the 10% percentile within the input frame. Expressed in
+range of [0-255].
+
+@item UAVG
+Display the average U value within the input frame. Expressed in range of
+[0-255].
+
+@item UHIGH
+Display the U value at the 90% percentile within the input frame. Expressed in
+range of [0-255].
+
+@item UMAX
+Display the maximum U value contained within the input frame. Expressed in
+range of [0-255].
+
+@item VMIN
+Display the minimal V value contained within the input frame. Expressed in
+range of [0-255].
+
+@item VLOW
+Display the V value at the 10% percentile within the input frame. Expressed in
+range of [0-255].
+
+@item VAVG
+Display the average V value within the input frame. Expressed in range of
+[0-255].
+
+@item VHIGH
+Display the V value at the 90% percentile within the input frame. Expressed in
+range of [0-255].
+
+@item VMAX
+Display the maximum V value contained within the input frame. Expressed in
+range of [0-255].
+
+@item SATMIN
+Display the minimal saturation value contained within the input frame.
+Expressed in range of [0-~181.02].
+
+@item SATLOW
+Display the saturation value at the 10% percentile within the input frame.
+Expressed in range of [0-~181.02].
+
+@item SATAVG
+Display the average saturation value within the input frame. Expressed in range
+of [0-~181.02].
+
+@item SATHIGH
+Display the saturation value at the 90% percentile within the input frame.
+Expressed in range of [0-~181.02].
+
+@item SATMAX
+Display the maximum saturation value contained within the input frame.
+Expressed in range of [0-~181.02].
+
+@item HUEMED
+Display the median value for hue within the input frame. Expressed in range of
+[0-360].
+
+@item HUEAVG
+Display the average value for hue within the input frame. Expressed in range of
+[0-360].
+
+@item YDIF
+Display the average of sample value difference between all values of the Y
+plane in the current frame and corresponding values of the previous input frame.
+Expressed in range of [0-255].
+
+@item UDIF
+Display the average of sample value difference between all values of the U
+plane in the current frame and corresponding values of the previous input frame.
+Expressed in range of [0-255].
+
+@item VDIF
+Display the average of sample value difference between all values of the V
+plane in the current frame and corresponding values of the previous input frame.
+Expressed in range of [0-255].
+@end table
+
+The filter accepts the following options:
+
+@table @option
+@item stat
+@item out
+
+@option{stat} specify an additional form of image analysis.
+@option{out} output video with the specified type of pixel highlighted.
+
+Both options accept the following values:
+
+@table @samp
+@item tout
+Identify @var{temporal outliers} pixels. A @var{temporal outlier} is a pixel
+unlike the neighboring pixels of the same field. Examples of temporal outliers
+include the results of video dropouts, head clogs, or tape tracking issues.
+
+@item vrep
+Identify @var{vertical line repetition}. Vertical line repetition includes
+similar rows of pixels within a frame. In born-digital video vertical line
+repetition is common, but this pattern is uncommon in video digitized from an
+analog source. When it occurs in video that results from the digitization of an
+analog source it can indicate concealment from a dropout compensator.
+
+@item brng
+Identify pixels that fall outside of legal broadcast range.
+@end table
+
+@item color, c
+Set the highlight color for the @option{out} option. The default color is
+yellow.
+@end table
+
+@subsection Examples
+
+@itemize
+@item
+Output data of various video metrics:
+@example
+ffprobe -f lavfi movie=example.mov,signalstats="stat=tout+vrep+brng" -show_frames
+@end example
+
+@item
+Output specific data about the minimum and maximum values of the Y plane per frame:
+@example
+ffprobe -f lavfi movie=example.mov,signalstats -show_entries frame_tags=lavfi.signalstats.YMAX,lavfi.signalstats.YMIN
+@end example
+
+@item
+Playback video while highlighting pixels that are outside of broadcast range in red.
+@example
+ffplay example.mov -vf values="out=brng:color=red"
+@end example
+@end itemize
+
 @anchor{smartblur}
 @section smartblur
 
diff --git a/libavfilter/Makefile b/libavfilter/Makefile
index 9552b9f41b..5b9fabf89d 100644
--- a/libavfilter/Makefile
+++ b/libavfilter/Makefile
@@ -174,6 +174,7 @@ OBJS-$(CONFIG_SETSAR_FILTER)                 += vf_aspect.o
 OBJS-$(CONFIG_SETTB_FILTER)                  += settb.o
 OBJS-$(CONFIG_SHOWINFO_FILTER)               += vf_showinfo.o
 OBJS-$(CONFIG_SHUFFLEPLANES_FILTER)          += vf_shuffleplanes.o
+OBJS-$(CONFIG_SIGNALSTATS_FILTER)            += vf_signalstats.o
 OBJS-$(CONFIG_SMARTBLUR_FILTER)              += vf_smartblur.o
 OBJS-$(CONFIG_SPLIT_FILTER)                  += split.o
 OBJS-$(CONFIG_SPP_FILTER)                    += vf_spp.o
diff --git a/libavfilter/allfilters.c b/libavfilter/allfilters.c
index 9ef4f67aa8..1e86967be6 100644
--- a/libavfilter/allfilters.c
+++ b/libavfilter/allfilters.c
@@ -191,6 +191,7 @@ void avfilter_register_all(void)
     REGISTER_FILTER(SETTB,          settb,          vf);
     REGISTER_FILTER(SHOWINFO,       showinfo,       vf);
     REGISTER_FILTER(SHUFFLEPLANES,  shuffleplanes,  vf);
+    REGISTER_FILTER(SIGNALSTATS,    signalstats,    vf);
     REGISTER_FILTER(SMARTBLUR,      smartblur,      vf);
     REGISTER_FILTER(SPLIT,          split,          vf);
     REGISTER_FILTER(SPP,            spp,            vf);
diff --git a/libavfilter/version.h b/libavfilter/version.h
index 80a7b66f74..a518e8f6e2 100644
--- a/libavfilter/version.h
+++ b/libavfilter/version.h
@@ -30,7 +30,7 @@
 #include "libavutil/version.h"
 
 #define LIBAVFILTER_VERSION_MAJOR   4
-#define LIBAVFILTER_VERSION_MINOR   7
+#define LIBAVFILTER_VERSION_MINOR   8
 #define LIBAVFILTER_VERSION_MICRO 100
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \
diff --git a/libavfilter/vf_signalstats.c b/libavfilter/vf_signalstats.c
new file mode 100644
index 0000000000..263de23513
--- /dev/null
+++ b/libavfilter/vf_signalstats.c
@@ -0,0 +1,478 @@
+/*
+ * Copyright (c) 2010 Mark Heath mjpeg0 @ silicontrip dot org
+ * Copyright (c) 2014 Clément Bœsch
+ * Copyright (c) 2014 Dave Rice @dericed
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "libavutil/opt.h"
+#include "libavutil/pixdesc.h"
+#include "internal.h"
+
+enum FilterMode {
+    FILTER_NONE = -1,
+    FILTER_TOUT,
+    FILTER_VREP,
+    FILTER_BRNG,
+    FILT_NUMB
+};
+
+typedef struct {
+    const AVClass *class;
+    int chromah;    // height of chroma plane
+    int chromaw;    // width of chroma plane
+    int hsub;       // horizontal subsampling
+    int vsub;       // vertical subsampling
+    int fs;         // pixel count per frame
+    int cfs;        // pixel count per frame of chroma planes
+    enum FilterMode outfilter;
+    int filters;
+    AVFrame *frame_prev;
+    char *vrep_line;
+    uint8_t rgba_color[4];
+    int yuv_color[3];
+} SignalstatsContext;
+
+#define OFFSET(x) offsetof(SignalstatsContext, x)
+#define FLAGS AV_OPT_FLAG_FILTERING_PARAM|AV_OPT_FLAG_VIDEO_PARAM
+
+static const AVOption signalstats_options[] = {
+    {"stat", "set statistics filters", OFFSET(filters), AV_OPT_TYPE_FLAGS, {.i64=0}, 0, INT_MAX, FLAGS, "filters"},
+        {"tout", "analyze pixels for temporal outliers",                0, AV_OPT_TYPE_CONST, {.i64=1<<FILTER_TOUT}, 0, 0, FLAGS, "filters"},
+        {"vrep", "analyze video lines for vertical line repitition",    0, AV_OPT_TYPE_CONST, {.i64=1<<FILTER_VREP}, 0, 0, FLAGS, "filters"},
+        {"brng", "analyze for pixels outside of broadcast range",       0, AV_OPT_TYPE_CONST, {.i64=1<<FILTER_BRNG}, 0, 0, FLAGS, "filters"},
+    {"out", "set video filter", OFFSET(outfilter), AV_OPT_TYPE_INT, {.i64=FILTER_NONE}, -1, FILT_NUMB-1, FLAGS, "out"},
+        {"tout", "highlight pixels that depict temporal outliers",              0, AV_OPT_TYPE_CONST, {.i64=FILTER_TOUT}, 0, 0, FLAGS, "out"},
+        {"vrep", "highlight video lines that depict vertical line repitition",  0, AV_OPT_TYPE_CONST, {.i64=FILTER_VREP}, 0, 0, FLAGS, "out"},
+        {"brng", "highlight pixels that are outside of broadcast range",        0, AV_OPT_TYPE_CONST, {.i64=FILTER_BRNG}, 0, 0, FLAGS, "out"},
+    {"c",     "set highlight color", OFFSET(rgba_color), AV_OPT_TYPE_COLOR, {.str="yellow"}, .flags=FLAGS},
+    {"color", "set highlight color", OFFSET(rgba_color), AV_OPT_TYPE_COLOR, {.str="yellow"}, .flags=FLAGS},
+    {NULL}
+};
+
+AVFILTER_DEFINE_CLASS(signalstats);
+
+static av_cold int init(AVFilterContext *ctx)
+{
+    uint8_t r, g, b;
+    SignalstatsContext *s = ctx->priv;
+
+    if (s->outfilter != FILTER_NONE)
+        s->filters |= 1 << s->outfilter;
+
+    r = s->rgba_color[0];
+    g = s->rgba_color[1];
+    b = s->rgba_color[2];
+    s->yuv_color[0] = (( 66*r + 129*g +  25*b + (1<<7)) >> 8) +  16;
+    s->yuv_color[1] = ((-38*r + -74*g + 112*b + (1<<7)) >> 8) + 128;
+    s->yuv_color[2] = ((112*r + -94*g + -18*b + (1<<7)) >> 8) + 128;
+    return 0;
+}
+
+static av_cold void uninit(AVFilterContext *ctx)
+{
+    SignalstatsContext *s = ctx->priv;
+    av_frame_free(&s->frame_prev);
+    av_freep(&s->vrep_line);
+}
+
+static int query_formats(AVFilterContext *ctx)
+{
+    // TODO: add more
+    enum AVPixelFormat pix_fmts[] = {
+        AV_PIX_FMT_YUV444P, AV_PIX_FMT_YUV422P, AV_PIX_FMT_YUV420P, AV_PIX_FMT_YUV411P,
+        AV_PIX_FMT_NONE
+    };
+
+    ff_set_common_formats(ctx, ff_make_format_list(pix_fmts));
+    return 0;
+}
+
+static int config_props(AVFilterLink *outlink)
+{
+    AVFilterContext *ctx = outlink->src;
+    SignalstatsContext *s = ctx->priv;
+    AVFilterLink *inlink = outlink->src->inputs[0];
+    const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(outlink->format);
+    s->hsub = desc->log2_chroma_w;
+    s->vsub = desc->log2_chroma_h;
+
+    outlink->w = inlink->w;
+    outlink->h = inlink->h;
+
+    s->chromaw = FF_CEIL_RSHIFT(inlink->w, s->hsub);
+    s->chromah = FF_CEIL_RSHIFT(inlink->h, s->vsub);
+
+    s->fs = inlink->w * inlink->h;
+    s->cfs = s->chromaw * s->chromah;
+
+    if (s->filters & 1<<FILTER_VREP) {
+        s->vrep_line = av_malloc(inlink->h * sizeof(*s->vrep_line));
+        if (!s->vrep_line)
+            return AVERROR(ENOMEM);
+    }
+
+    return 0;
+}
+
+static void burn_frame(SignalstatsContext *s, AVFrame *f, int x, int y)
+{
+    const int chromax = x >> s->hsub;
+    const int chromay = y >> s->vsub;
+    f->data[0][y       * f->linesize[0] +       x] = s->yuv_color[0];
+    f->data[1][chromay * f->linesize[1] + chromax] = s->yuv_color[1];
+    f->data[2][chromay * f->linesize[2] + chromax] = s->yuv_color[2];
+}
+
+static int filter_brng(SignalstatsContext *s, const AVFrame *in, AVFrame *out, int y, int w, int h)
+{
+    int x, score = 0;
+    const int yc = y >> s->vsub;
+    const uint8_t *pluma    = &in->data[0][y  * in->linesize[0]];
+    const uint8_t *pchromau = &in->data[1][yc * in->linesize[1]];
+    const uint8_t *pchromav = &in->data[2][yc * in->linesize[2]];
+
+    for (x = 0; x < w; x++) {
+        const int xc = x >> s->hsub;
+        const int luma    = pluma[x];
+        const int chromau = pchromau[xc];
+        const int chromav = pchromav[xc];
+        const int filt = luma    < 16 || luma    > 235 ||
+                         chromau < 16 || chromau > 240 ||
+                         chromav < 16 || chromav > 240;
+        score += filt;
+        if (out && filt)
+            burn_frame(s, out, x, y);
+    }
+    return score;
+}
+
+static int filter_tout_outlier(uint8_t x, uint8_t y, uint8_t z)
+{
+    return ((abs(x - y) + abs (z - y)) / 2) - abs(z - x) > 4; // make 4 configurable?
+}
+
+static int filter_tout(SignalstatsContext *s, const AVFrame *in, AVFrame *out, int y, int w, int h)
+{
+    const uint8_t *p = in->data[0];
+    int lw = in->linesize[0];
+    int x, score = 0, filt;
+
+    if (y - 1 < 0 || y + 1 >= h)
+        return 0;
+
+    // detect two pixels above and below (to eliminate interlace artefacts)
+    // should check that video format is infact interlaced.
+
+#define FILTER(i, j) \
+filter_tout_outlier(p[(y-j) * lw + x + i], \
+                    p[    y * lw + x + i], \
+                    p[(y+j) * lw + x + i])
+
+#define FILTER3(j) (FILTER(-1, j) && FILTER(0, j) && FILTER(1, j))
+
+    if (y - 2 >= 0 && y + 2 < h) {
+        for (x = 1; x < w - 1; x++) {
+            filt = FILTER3(2) && FILTER3(1);
+            score += filt;
+            if (filt && out)
+                burn_frame(s, out, x, y);
+        }
+    } else {
+        for (x = 1; x < w - 1; x++) {
+            filt = FILTER3(1);
+            score += filt;
+            if (filt && out)
+                burn_frame(s, out, x, y);
+        }
+    }
+    return score;
+}
+
+#define VREP_START 4
+
+static void filter_init_vrep(SignalstatsContext *s, const AVFrame *p, int w, int h)
+{
+    int i, y;
+    int lw = p->linesize[0];
+
+    for (y = VREP_START; y < h; y++) {
+        int totdiff = 0;
+        int y2lw = (y - VREP_START) * lw;
+        int ylw = y * lw;
+
+        for (i = 0; i < w; i++)
+            totdiff += abs(p->data[0][y2lw + i] - p->data[0][ylw + i]);
+
+        /* this value should be definable */
+        s->vrep_line[y] = totdiff < w;
+    }
+}
+
+static int filter_vrep(SignalstatsContext *s, const AVFrame *in, AVFrame *out, int y, int w, int h)
+{
+    int x, score = 0;
+
+    if (y < VREP_START)
+        return 0;
+
+    for (x = 0; x < w; x++) {
+        if (s->vrep_line[y]) {
+            score++;
+            if (out)
+                burn_frame(s, out, x, y);
+        }
+    }
+    return score;
+}
+
+static const struct {
+    const char *name;
+    void (*init)(SignalstatsContext *s, const AVFrame *p, int w, int h);
+    int (*process)(SignalstatsContext *s, const AVFrame *in, AVFrame *out, int y, int w, int h);
+} filters_def[] = {
+    {"TOUT", NULL,              filter_tout},
+    {"VREP", filter_init_vrep,  filter_vrep},
+    {"BRNG", NULL,              filter_brng},
+    {NULL}
+};
+
+#define DEPTH 256
+
+static int filter_frame(AVFilterLink *link, AVFrame *in)
+{
+    SignalstatsContext *s = link->dst->priv;
+    AVFilterLink *outlink = link->dst->outputs[0];
+    AVFrame *out = in;
+    int i, j;
+    int  w = 0,  cw = 0, // in
+        pw = 0, cpw = 0; // prev
+    int yuv, yuvu, yuvv;
+    int fil;
+    char metabuf[128];
+    unsigned int histy[DEPTH] = {0},
+                 histu[DEPTH] = {0},
+                 histv[DEPTH] = {0},
+                 histhue[360] = {0},
+                 histsat[DEPTH] = {0}; // limited to 8 bit data.
+    int miny  = -1, minu  = -1, minv  = -1;
+    int maxy  = -1, maxu  = -1, maxv  = -1;
+    int lowy  = -1, lowu  = -1, lowv  = -1;
+    int highy = -1, highu = -1, highv = -1;
+    int minsat = -1, maxsat = -1, lowsat = -1, highsat = -1;
+    int lowp, highp, clowp, chighp;
+    int accy, accu, accv;
+    int accsat, acchue = 0;
+    int medhue, maxhue;
+    int toty = 0, totu = 0, totv = 0, totsat=0;
+    int tothue = 0;
+    int dify = 0, difu = 0, difv = 0;
+
+    int filtot[FILT_NUMB] = {0};
+    AVFrame *prev;
+
+    if (!s->frame_prev)
+        s->frame_prev = av_frame_clone(in);
+
+    prev = s->frame_prev;
+
+    if (s->outfilter != FILTER_NONE)
+        out = av_frame_clone(in);
+
+    for (fil = 0; fil < FILT_NUMB; fil ++)
+        if ((s->filters & 1<<fil) && filters_def[fil].init)
+            filters_def[fil].init(s, in, link->w, link->h);
+
+    // Calculate luma histogram and difference with previous frame or field.
+    for (j = 0; j < link->h; j++) {
+        for (i = 0; i < link->w; i++) {
+            yuv = in->data[0][w + i];
+            histy[yuv]++;
+            dify += abs(in->data[0][w + i] - prev->data[0][pw + i]);
+        }
+        w  += in->linesize[0];
+        pw += prev->linesize[0];
+    }
+
+    // Calculate chroma histogram and difference with previous frame or field.
+    for (j = 0; j < s->chromah; j++) {
+        for (i = 0; i < s->chromaw; i++) {
+            int sat, hue;
+
+            yuvu = in->data[1][cw+i];
+            yuvv = in->data[2][cw+i];
+            histu[yuvu]++;
+            difu += abs(in->data[1][cw+i] - prev->data[1][cpw+i]);
+            histv[yuvv]++;
+            difv += abs(in->data[2][cw+i] - prev->data[2][cpw+i]);
+
+            // int or round?
+            sat = hypot(yuvu - 128, yuvv - 128);
+            histsat[sat]++;
+            hue = floor((180 / M_PI) * atan2f(yuvu-128, yuvv-128) + 180);
+            histhue[hue]++;
+        }
+        cw  += in->linesize[1];
+        cpw += prev->linesize[1];
+    }
+
+    for (j = 0; j < link->h; j++) {
+        for (fil = 0; fil < FILT_NUMB; fil ++) {
+            if (s->filters & 1<<fil) {
+                AVFrame *dbg = out != in && s->outfilter == fil ? out : NULL;
+                filtot[fil] += filters_def[fil].process(s, in, dbg, j, link->w, link->h);
+            }
+        }
+    }
+
+    // find low / high based on histogram percentile
+    // these only need to be calculated once.
+
+    lowp   = lrint(s->fs  * 10 / 100.);
+    highp  = lrint(s->fs  * 90 / 100.);
+    clowp  = lrint(s->cfs * 10 / 100.);
+    chighp = lrint(s->cfs * 90 / 100.);
+
+    accy = accu = accv = accsat = 0;
+    for (fil = 0; fil < DEPTH; fil++) {
+        if (miny   < 0 && histy[fil])   miny = fil;
+        if (minu   < 0 && histu[fil])   minu = fil;
+        if (minv   < 0 && histv[fil])   minv = fil;
+        if (minsat < 0 && histsat[fil]) minsat = fil;
+
+        if (histy[fil])   maxy   = fil;
+        if (histu[fil])   maxu   = fil;
+        if (histv[fil])   maxv   = fil;
+        if (histsat[fil]) maxsat = fil;
+
+        toty   += histy[fil]   * fil;
+        totu   += histu[fil]   * fil;
+        totv   += histv[fil]   * fil;
+        totsat += histsat[fil] * fil;
+
+        accy   += histy[fil];
+        accu   += histu[fil];
+        accv   += histv[fil];
+        accsat += histsat[fil];
+
+        if (lowy   == -1 && accy   >=  lowp) lowy   = fil;
+        if (lowu   == -1 && accu   >= clowp) lowu   = fil;
+        if (lowv   == -1 && accv   >= clowp) lowv   = fil;
+        if (lowsat == -1 && accsat >= clowp) lowsat = fil;
+
+        if (highy   == -1 && accy   >=  highp) highy   = fil;
+        if (highu   == -1 && accu   >= chighp) highu   = fil;
+        if (highv   == -1 && accv   >= chighp) highv   = fil;
+        if (highsat == -1 && accsat >= chighp) highsat = fil;
+    }
+
+    maxhue = histhue[0];
+    medhue = -1;
+    for (fil = 0; fil < 360; fil++) {
+        tothue += histhue[fil] * fil;
+        acchue += histhue[fil];
+
+        if (medhue == -1 && acchue > s->cfs / 2)
+            medhue = fil;
+        if (histhue[fil] > maxhue) {
+            maxhue = histhue[fil];
+        }
+    }
+
+    av_frame_free(&s->frame_prev);
+    s->frame_prev = av_frame_clone(in);
+
+#define SET_META(key, fmt, val) do {                                \
+    snprintf(metabuf, sizeof(metabuf), fmt, val);                   \
+    av_dict_set(&out->metadata, "lavfi.signalstats." key, metabuf, 0);   \
+} while (0)
+
+    SET_META("YMIN",    "%d", miny);
+    SET_META("YLOW",    "%d", lowy);
+    SET_META("YAVG",    "%g", 1.0 * toty / s->fs);
+    SET_META("YHIGH",   "%d", highy);
+    SET_META("YMAX",    "%d", maxy);
+
+    SET_META("UMIN",    "%d", minu);
+    SET_META("ULOW",    "%d", lowu);
+    SET_META("UAVG",    "%g", 1.0 * totu / s->cfs);
+    SET_META("UHIGH",   "%d", highu);
+    SET_META("UMAX",    "%d", maxu);
+
+    SET_META("VMIN",    "%d", minv);
+    SET_META("VLOW",    "%d", lowv);
+    SET_META("VAVG",    "%g", 1.0 * totv / s->cfs);
+    SET_META("VHIGH",   "%d", highv);
+    SET_META("VMAX",    "%d", maxv);
+
+    SET_META("SATMIN",  "%d", minsat);
+    SET_META("SATLOW",  "%d", lowsat);
+    SET_META("SATAVG",  "%g", 1.0 * totsat / s->cfs);
+    SET_META("SATHIGH", "%d", highsat);
+    SET_META("SATMAX",  "%d", maxsat);
+
+    SET_META("HUEMED",  "%d", medhue);
+    SET_META("HUEAVG",  "%g", 1.0 * tothue / s->cfs);
+
+    SET_META("YDIF",    "%g", 1.0 * dify / s->fs);
+    SET_META("UDIF",    "%g", 1.0 * difu / s->cfs);
+    SET_META("VDIF",    "%g", 1.0 * difv / s->cfs);
+
+    for (fil = 0; fil < FILT_NUMB; fil ++) {
+        if (s->filters & 1<<fil) {
+            char metaname[128];
+            snprintf(metabuf,  sizeof(metabuf),  "%g", 1.0 * filtot[fil] / s->fs);
+            snprintf(metaname, sizeof(metaname), "lavfi.signalstats.%s", filters_def[fil].name);
+            av_dict_set(&out->metadata, metaname, metabuf, 0);
+        }
+    }
+
+    if (in != out)
+        av_frame_free(&in);
+    return ff_filter_frame(outlink, out);
+}
+
+static const AVFilterPad signalstats_inputs[] = {
+    {
+        .name           = "default",
+        .type           = AVMEDIA_TYPE_VIDEO,
+        .filter_frame   = filter_frame,
+    },
+    { NULL }
+};
+
+static const AVFilterPad signalstats_outputs[] = {
+    {
+        .name           = "default",
+        .config_props   = config_props,
+        .type           = AVMEDIA_TYPE_VIDEO,
+    },
+    { NULL }
+};
+
+AVFilter ff_vf_signalstats = {
+    .name          = "signalstats",
+    .description   = "Generate statistics from video analysis.",
+    .init          = init,
+    .uninit        = uninit,
+    .query_formats = query_formats,
+    .priv_size     = sizeof(SignalstatsContext),
+    .inputs        = signalstats_inputs,
+    .outputs       = signalstats_outputs,
+    .priv_class    = &signalstats_class,
+};