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/*

 * Copyright (c) 2011 Smartjog S.A.S, Clément Bœsch 

 *

 * 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 .

 * @see http://notbrainsurgery.livejournal.com/29773.html

 */

#include "libavutil/opt.h"

#include "avfilter.h"

#include "internal.h"

#define HIST_SIZE (3*256)

struct thumb_frame {

    AVFrame *buf;               ///< cached frame

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

};

typedef struct {

    const AVClass *class;

    int n;                      ///< current frame

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

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

    AVRational tb;              ///< copy of the input timebase to ease access

} ThumbContext;

#define OFFSET(x) offsetof(ThumbContext, x)

#define FLAGS AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_FILTERING_PARAM

static const AVOption thumbnail_options[] = {

    { "n", "set the frames batch size", OFFSET(n_frames), AV_OPT_TYPE_INT, {.i64=100}, 2, INT_MAX, FLAGS },

    { NULL }

};

AVFILTER_DEFINE_CLASS(thumbnail);

static av_cold int init(AVFilterContext *ctx)

{

    ThumbContext *thumb = ctx->priv;

    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_VERBOSE, "batch size: %d frames\n", thumb->n_frames);

    return 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 AVFrame *get_best_frame(AVFilterContext *ctx)

{

    AVFrame *picref;

    ThumbContext *thumb = ctx->priv;

    int i, j, best_frame_idx = 0;

    int nb_frames = thumb->n;

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

    // average histogram of the N frames

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

        for (i = 0; i < nb_frames; i++)

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

        avg_hist[j] /= nb_frames;

    }

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

    for (i = 0; i < nb_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 < nb_frames; i++) {

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

        if (i != best_frame_idx)

            av_frame_free(&thumb->frames[i].buf);

    }

    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 "

           "from a set of %d images\n", best_frame_idx,

           picref->pts * av_q2d(thumb->tb), nb_frames);

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

    return picref;

}

static int filter_frame(AVFilterLink *inlink, AVFrame *frame)

{

    int i, j;

    AVFilterContext *ctx  = inlink->dst;

    ThumbContext *thumb   = ctx->priv;

    AVFilterLink *outlink = ctx->outputs[0];

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

    const uint8_t *p = frame->data[0];

    // keep a reference of each frame

    thumb->frames[thumb->n].buf = frame;

    // update current frame RGB histogram

    for (j = 0; j < inlink->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 += frame->linesize[0];

    }

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

    thumb->n++;

    if (thumb->n < thumb->n_frames)

        return 0;

    return ff_filter_frame(outlink, get_best_frame(ctx));

}

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++)

        av_frame_free(&thumb->frames[i].buf);

    av_freep(&thumb->frames);

}

static int request_frame(AVFilterLink *link)

{

    AVFilterContext *ctx = link->src;

    ThumbContext *thumb = ctx->priv;

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

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

    do {

        int ret = ff_request_frame(ctx->inputs[0]);

        if (ret == AVERROR_EOF && thumb->n) {

            ret = ff_filter_frame(link, get_best_frame(ctx));

            if (ret < 0)

                return ret;

            ret = AVERROR_EOF;

        }

        if (ret < 0)

            return ret;

    } while (thumb->n);

    return 0;

}

static int config_props(AVFilterLink *inlink)

{

    AVFilterContext *ctx = inlink->dst;

    ThumbContext *thumb = ctx->priv;

    thumb->tb = inlink->time_base;

    return 0;

}

static int query_formats(AVFilterContext *ctx)

{

    static const enum AVPixelFormat pix_fmts[] = {

        AV_PIX_FMT_RGB24, AV_PIX_FMT_BGR24,

        AV_PIX_FMT_NONE

    };

    ff_set_common_formats(ctx, ff_make_format_list(pix_fmts));

    return 0;

}

static const AVFilterPad thumbnail_inputs[] = {

    {

        .name         = "default",

        .type         = AVMEDIA_TYPE_VIDEO,

        .config_props = config_props,

        .filter_frame = filter_frame,

    },

    { NULL }

};

static const AVFilterPad thumbnail_outputs[] = {

    {

        .name          = "default",

        .type          = AVMEDIA_TYPE_VIDEO,

        .request_frame = request_frame,

    },

    { NULL }

};

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        = thumbnail_inputs,

    .outputs       = thumbnail_outputs,

    .priv_class    = &thumbnail_class,

};