@@ -144,6 +144,7 @@ easier to use. The changes are:

 - Dxtory capture format decoder

 - cellauto source

 - Simple segmenting muxer

+- thumbnail video filter

 version 0.8:

@@ -2400,6 +2400,26 @@ For example:

 will create two separate outputs from the same input, one cropped and

 one padded.

+@section thumbnail

+Select the most representative frame in a given sequence of consecutive frames.

+

+It accepts as argument the frames batch size to analyze (default @var{N}=100);

+in a set of @var{N} frames, the filter will pick one of them, and then handle

+the next batch of @var{N} frames until the end.

+

+Since the filter keeps track of the whole frames sequence, a bigger @var{N}

+value will result in a higher memory usage, so a high value is not recommended.

+

+The following example extract one picture each 50 frames:

+@example

+thumbnail=50

+@end example

+

+Complete example of a thumbnail creation with @command{ffmpeg}:

+@example

+ffmpeg -i in.avi -vf thumbnail,scale=300:200 -frames:v 1 out.png

+@end example

+

 @section transpose

 Transpose rows with columns in the input video and optionally flip it.

@@ -79,6 +79,7 @@ OBJS-$(CONFIG_SETTB_FILTER)                  += vf_settb.o

 OBJS-$(CONFIG_SHOWINFO_FILTER)               += vf_showinfo.o

 OBJS-$(CONFIG_SLICIFY_FILTER)                += vf_slicify.o

 OBJS-$(CONFIG_SPLIT_FILTER)                  += vf_split.o

+OBJS-$(CONFIG_THUMBNAIL_FILTER)              += vf_thumbnail.o

 OBJS-$(CONFIG_TRANSPOSE_FILTER)              += vf_transpose.o

 OBJS-$(CONFIG_UNSHARP_FILTER)                += vf_unsharp.o

 OBJS-$(CONFIG_VFLIP_FILTER)                  += vf_vflip.o

@@ -89,6 +89,7 @@ void avfilter_register_all(void)

     REGISTER_FILTER (SHOWINFO,    showinfo,    vf);

     REGISTER_FILTER (SLICIFY,     slicify,     vf);

     REGISTER_FILTER (SPLIT,       split,       vf);

+    REGISTER_FILTER (THUMBNAIL,   thumbnail,   vf);

     REGISTER_FILTER (TRANSPOSE,   transpose,   vf);

     REGISTER_FILTER (UNSHARP,     unsharp,     vf);

     REGISTER_FILTER (VFLIP,       vflip,       vf);

new file mode 100644

@@ -0,0 +1,243 @@

+/*

+ * Copyright (c) 2011 Smartjog S.A.S, Clément Bœsch <clement.boesch@smartjog.com>

+ *

+ * 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

+ */

+

+/**

+ * @file

+ * Potential thumbnail lookup filter to reduce the risk of an inappropriate

+ * selection (such as a black frame) we could get with an absolute seek.

+ *

+ * Simplified version of algorithm by Vadim Zaliva <lord@crocodile.org>.

+ * @url http://notbrainsurgery.livejournal.com/29773.html

+ */

+

+#include "avfilter.h"

+

+#define HIST_SIZE (3*256)

+

+struct thumb_frame {

+    AVFilterBufferRef *buf;     ///< cached frame

+    int histogram[HIST_SIZE];   ///< RGB color distribution histogram of the frame

+};

+

+typedef struct {

+    int n;                      ///< current frame

+    int n_frames;               ///< number of frames for analysis

+    struct thumb_frame *frames; ///< the n_frames frames

+} ThumbContext;

+

+static av_cold int init(AVFilterContext *ctx, const char *args, void *opaque)

+{

+    ThumbContext *thumb = ctx->priv;

+

+    if (!args) {

+        thumb->n_frames = 100;

+    } else {

+        int n = sscanf(args, "%d", &thumb->n_frames);

+        if (n != 1 || thumb->n_frames < 2) {

+            thumb->n_frames = 0;

+            av_log(ctx, AV_LOG_ERROR,

+                   "Invalid number of frames specified (minimum is 2).\n");

+            return AVERROR(ENOMEM);

+        }

+    }

+    thumb->frames = av_calloc(thumb->n_frames, sizeof(*thumb->frames));

+    if (!thumb->frames) {

+        av_log(ctx, AV_LOG_ERROR,

+               "Allocation failure, try to lower the number of frames\n");

+        return AVERROR(ENOMEM);

+    }

+    av_log(ctx, AV_LOG_INFO, "batch size: %d frames\n", thumb->n_frames);

+    return 0;

+}

+

+static void draw_slice(AVFilterLink *inlink, int y, int h, int slice_dir)

+{

+    int i, j;

+    AVFilterContext *ctx = inlink->dst;

+    ThumbContext *thumb = ctx->priv;

+    int *hist = thumb->frames[thumb->n].histogram;

+    AVFilterBufferRef *picref = inlink->cur_buf;

+    const uint8_t *p = picref->data[0] + y * picref->linesize[0];

+

+    // update current frame RGB histogram

+    for (j = 0; j < h; j++) {

+        for (i = 0; i < inlink->w; i++) {

+            hist[0*256 + p[i*3    ]]++;

+            hist[1*256 + p[i*3 + 1]]++;

+            hist[2*256 + p[i*3 + 2]]++;

+        }

+        p += picref->linesize[0];

+    }

+}

+

+/**

+ * @brief        Compute Sum-square deviation to estimate "closeness".

+ * @param hist   color distribution histogram

+ * @param median average color distribution histogram

+ * @return       sum of squared errors

+ */

+static double frame_sum_square_err(const int *hist, const double *median)

+{

+    int i;

+    double err, sum_sq_err = 0;

+

+    for (i = 0; i < HIST_SIZE; i++) {

+        err = median[i] - (double)hist[i];

+        sum_sq_err += err*err;

+    }

+    return sum_sq_err;

+}

+

+static void end_frame(AVFilterLink *inlink)

+{

+    int i, j, best_frame_idx = 0;

+    double avg_hist[HIST_SIZE] = {0}, sq_err, min_sq_err = -1;

+    AVFilterLink *outlink = inlink->dst->outputs[0];

+    ThumbContext *thumb   = inlink->dst->priv;

+    AVFilterContext *ctx  = inlink->dst;

+    AVFilterBufferRef *picref;

+

+    // keep a reference of each frame

+    thumb->frames[thumb->n].buf = inlink->cur_buf;

+

+    // no selection until the buffer of N frames is filled up

+    if (thumb->n < thumb->n_frames - 1) {

+        thumb->n++;

+        return;

+    }

+

+    // average histogram of the N frames

+    for (j = 0; j < FF_ARRAY_ELEMS(avg_hist); j++) {

+        for (i = 0; i < thumb->n_frames; i++)

+            avg_hist[j] += (double)thumb->frames[i].histogram[j];

+        avg_hist[j] /= thumb->n_frames;

+    }

+

+    // find the frame closer to the average using the sum of squared errors

+    for (i = 0; i < thumb->n_frames; i++) {

+        sq_err = frame_sum_square_err(thumb->frames[i].histogram, avg_hist);

+        if (i == 0 || sq_err < min_sq_err)

+            best_frame_idx = i, min_sq_err = sq_err;

+    }

+

+    // free and reset everything (except the best frame buffer)

+    for (i = 0; i < thumb->n_frames; i++) {

+        memset(thumb->frames[i].histogram, 0, sizeof(thumb->frames[i].histogram));

+        if (i == best_frame_idx)

+            continue;

+        avfilter_unref_buffer(thumb->frames[i].buf);

+        thumb->frames[i].buf = NULL;

+    }

+    thumb->n = 0;

+

+    // raise the chosen one

+    picref = thumb->frames[best_frame_idx].buf;

+    av_log(ctx, AV_LOG_INFO, "frame id #%d (pts_time=%f) selected\n",

+           best_frame_idx, picref->pts * av_q2d(inlink->time_base));

+    avfilter_start_frame(outlink, picref);

+    thumb->frames[best_frame_idx].buf = NULL;

+    avfilter_draw_slice(outlink, 0, inlink->h, 1);

+    avfilter_end_frame(outlink);

+}

+

+static av_cold void uninit(AVFilterContext *ctx)

+{

+    int i;

+    ThumbContext *thumb = ctx->priv;

+    for (i = 0; i < thumb->n_frames && thumb->frames[i].buf; i++) {

+        avfilter_unref_buffer(thumb->frames[i].buf);

+        thumb->frames[i].buf = NULL;

+    }

+    av_freep(&thumb->frames);

+}

+

+static void null_start_frame(AVFilterLink *link, AVFilterBufferRef *picref) { }

+

+static int request_frame(AVFilterLink *link)

+{

+    ThumbContext *thumb = link->src->priv;

+

+    /* loop until a frame thumbnail is available (when a frame is queued,

+     * thumb->n is reset to zero) */

+    while (thumb->n) {

+        int ret = avfilter_request_frame(link->src->inputs[0]);

+        if (ret < 0)

+            return ret;

+    }

+    return 0;

+}

+

+static int poll_frame(AVFilterLink *link)

+{

+    ThumbContext *thumb  = link->src->priv;

+    AVFilterLink *inlink = link->src->inputs[0];

+    int ret, available_frames = avfilter_poll_frame(inlink);

+

+    /* If the input link is not able to provide any frame, we can't do anything

+     * at the moment and thus have zero thumbnail available. */

+    if (!available_frames)

+        return 0;

+

+    /* Since at least one frame is available and the next frame will allow us

+     * to compute a thumbnail, we can return 1 frame. */

+    if (thumb->n == thumb->n_frames - 1)

+        return 1;

+

+    /* we have some frame(s) available in the input link, but not yet enough to

+     * output a thumbnail, so we request more */

+    ret = avfilter_request_frame(inlink);

+    return ret < 0 ? ret : 0;

+}

+

+static int query_formats(AVFilterContext *ctx)

+{

+    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_thumbnail = {

+    .name          = "thumbnail",

+    .description   = NULL_IF_CONFIG_SMALL("Select the most representative frame in a given sequence of consecutive frames."),

+    .priv_size     = sizeof(ThumbContext),

+    .init          = init,

+    .uninit        = uninit,

+    .query_formats = query_formats,

+    .inputs        = (const AVFilterPad[]) {

+        {   .name             = "default",

+            .type             = AVMEDIA_TYPE_VIDEO,

+            .get_video_buffer = avfilter_null_get_video_buffer,

+            .start_frame      = null_start_frame,

+            .draw_slice       = draw_slice,

+            .end_frame        = end_frame,

+        },{ .name = NULL }

+    },

+    .outputs       = (const AVFilterPad[]) {

+        {   .name             = "default",

+            .type             = AVMEDIA_TYPE_VIDEO,

+            .request_frame    = request_frame,

+            .poll_frame       = poll_frame,

+            .rej_perms        = AV_PERM_REUSE2,

+        },{ .name = NULL }

+    },

+};