@@ -3,6 +3,7 @@ releases are sorted from youngest to oldest.

 version next:

 - INI output in ffprobe

+- Scene detection in libavfilter

 version 0.11:

@@ -1708,6 +1708,7 @@ ocv_filter_deps="libopencv"

 pan_filter_deps="swresample"

 removelogo_filter_deps="avcodec avformat swscale"

 scale_filter_deps="swscale"

+select_filter_deps="avcodec"

 super2xsai_filter_deps="gpl"

 tinterlace_filter_deps="gpl"

 yadif_filter_deps="gpl"

@@ -2603,6 +2603,12 @@ the frame is bottom-field-first

 @item pos

 the position in the file of the filtered frame, -1 if the information

 is not available (e.g. for synthetic video)

+

+@item scene

+value between 0 and 1 to indicate a new scene; a low value reflects a low

+probability for the current frame to introduce a new scene, while a higher

+value means the current frame is more likely to be one (see the example below)

+

 @end table

 The default value of the select expression is "1".

@@ -2635,6 +2641,15 @@ select='gte(t\,10)*lte(t\,20)*eq(pict_type\,I)'

 select='isnan(prev_selected_t)+gte(t-prev_selected_t\,10)'

 @end example

+Complete example to create a mosaic of the first scenes:

+

+@example

+ffmpeg -i video.avi -vf select='gt(scene\,0.4)',scale=160:120,tile -frames:v 1 preview.png

+@end example

+

+Comparing @var{scene} against a value between 0.3 and 0.5 is generally a sane

+choice.

+

 @section setdar, setsar

 The @code{setdar} filter sets the Display Aspect Ratio for the filter

@@ -25,7 +25,9 @@

 #include "libavutil/eval.h"

 #include "libavutil/fifo.h"

+#include "libavcodec/dsputil.h"

 #include "avfilter.h"

+#include "formats.h"

 #include "video.h"

 static const char *const var_names[] = {

@@ -62,6 +64,8 @@ static const char *const var_names[] = {

     "key",               ///< tell if the frame is a key frame

     "pos",               ///< original position in the file of the frame

+    "scene",

+

     NULL

 };

@@ -99,6 +103,8 @@ enum var_name {

     VAR_KEY,

     VAR_POS,

+    VAR_SCENE,

+

     VAR_VARS_NB

 };

@@ -107,6 +113,11 @@ enum var_name {

 typedef struct {

     AVExpr *expr;

     double var_values[VAR_VARS_NB];

+    int do_scene_detect;            ///< 1 if the expression requires scene detection variables, 0 otherwise

+    AVCodecContext *avctx;          ///< codec context required for the DSPContext (scene detect only)

+    DSPContext c;                   ///< context providing optimized SAD methods   (scene detect only)

+    double prev_mafd;               ///< previous MAFD                             (scene detect only)

+    AVFilterBufferRef *prev_picref; ///< previous frame                            (scene detect only)

     double select;

     int cache_frames;

     AVFifoBuffer *pending_frames; ///< FIFO buffer of video frames

@@ -128,6 +139,8 @@ static av_cold int init(AVFilterContext *ctx, const char *args, void *opaque)

         av_log(ctx, AV_LOG_ERROR, "Failed to allocate pending frames buffer.\n");

         return AVERROR(ENOMEM);

     }

+

+    select->do_scene_detect = args && strstr(args, "scene");

     return 0;

 }

@@ -160,9 +173,49 @@ static int config_input(AVFilterLink *inlink)

     select->var_values[VAR_INTERLACE_TYPE_T] = INTERLACE_TYPE_T;

     select->var_values[VAR_INTERLACE_TYPE_B] = INTERLACE_TYPE_B;

+    if (select->do_scene_detect) {

+        select->avctx = avcodec_alloc_context3(NULL);

+        if (!select->avctx)

+            return AVERROR(ENOMEM);

+        ff_dsputil_init(&select->c, select->avctx);

+    }

     return 0;

 }

+static double get_scene_score(AVFilterContext *ctx, AVFilterBufferRef *picref)

+{

+    double ret = 0;

+    SelectContext *select = ctx->priv;

+    AVFilterBufferRef *prev_picref = select->prev_picref;

+

+    if (prev_picref &&

+        picref->video->h    == prev_picref->video->h &&

+        picref->video->w    == prev_picref->video->w &&

+        picref->linesize[0] == prev_picref->linesize[0]) {

+        int x, y;

+        int64_t sad;

+        double mafd, diff;

+        uint8_t *p1 =      picref->data[0];

+        uint8_t *p2 = prev_picref->data[0];

+        const int linesize = picref->linesize[0];

+

+        for (sad = y = 0; y < picref->video->h; y += 8)

+            for (x = 0; x < linesize; x += 8)

+                sad += select->c.sad[1](select,

+                                        p1 + y * linesize + x,

+                                        p2 + y * linesize + x,

+                                        linesize, 8);

+        emms_c();

+        mafd = sad / (picref->video->h * picref->video->w * 3);

+        diff = llabs(mafd - select->prev_mafd);

+        ret  = av_clipf(FFMIN(mafd, diff) / 100., 0, 1);

+        select->prev_mafd = mafd;

+        avfilter_unref_buffer(prev_picref);

+    }

+    select->prev_picref = avfilter_ref_buffer(picref, ~0);

+    return ret;

+}

+

 #define D2TS(d)  (isnan(d) ? AV_NOPTS_VALUE : (int64_t)(d))

 #define TS2D(ts) ((ts) == AV_NOPTS_VALUE ? NAN : (double)(ts))

@@ -172,6 +225,8 @@ static int select_frame(AVFilterContext *ctx, AVFilterBufferRef *picref)

     AVFilterLink *inlink = ctx->inputs[0];

     double res;

+    if (select->do_scene_detect)

+        select->var_values[VAR_SCENE] = get_scene_score(ctx, picref);

     if (isnan(select->var_values[VAR_START_PTS]))

         select->var_values[VAR_START_PTS] = TS2D(picref->pts);

     if (isnan(select->var_values[VAR_START_T]))

@@ -315,6 +370,28 @@ static av_cold void uninit(AVFilterContext *ctx)

         avfilter_unref_buffer(picref);

     av_fifo_free(select->pending_frames);

     select->pending_frames = NULL;

+

+    if (select->do_scene_detect) {

+        avfilter_unref_bufferp(&select->prev_picref);

+        avcodec_close(select->avctx);

+        av_freep(&select->avctx);

+    }

+}

+

+static int query_formats(AVFilterContext *ctx)

+{

+    SelectContext *select = ctx->priv;

+

+    if (!select->do_scene_detect) {

+        return ff_default_query_formats(ctx);

+    } else {

+        static const enum PixelFormat pix_fmts[] = {

+            PIX_FMT_RGB24, PIX_FMT_BGR24,

+            PIX_FMT_NONE

+        };

+        avfilter_set_common_pixel_formats(ctx, avfilter_make_format_list(pix_fmts));

+    }

+    return 0;

 }

 AVFilter avfilter_vf_select = {

@@ -322,6 +399,7 @@ AVFilter avfilter_vf_select = {

     .description = NULL_IF_CONFIG_SMALL("Select frames to pass in output."),

     .init      = init,

     .uninit    = uninit,

+    .query_formats = query_formats,

     .priv_size = sizeof(SelectContext),