/*
  * 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>.

  * @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 ThumbContext {

     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 *s = ctx->priv;

     s->frames = av_calloc(s->n_frames, sizeof(*s->frames));
     if (!s->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", s->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 *s = ctx->priv;

     int i, j, best_frame_idx = 0;

     int nb_frames = s->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)s->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(s->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(s->frames[i].histogram, 0, sizeof(s->frames[i].histogram));

         if (i != best_frame_idx)

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

     }

     s->n = 0;

 
     // raise the chosen one

     picref = s->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(s->tb), nb_frames);
     s->frames[best_frame_idx].buf = NULL;

 
     return picref;
 }
 
 static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
 {
     int i, j;

     AVFilterContext *ctx  = inlink->dst;

     ThumbContext *s   = ctx->priv;

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

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

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

 
     // keep a reference of each frame

     s->frames[s->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

     s->n++;
     if (s->n < s->n_frames)

         return 0;

     return ff_filter_frame(outlink, get_best_frame(ctx));

 }
 
 static av_cold void uninit(AVFilterContext *ctx)
 {
     int i;

     ThumbContext *s = ctx->priv;
     for (i = 0; i < s->n_frames && s->frames[i].buf; i++)
         av_frame_free(&s->frames[i].buf);
     av_freep(&s->frames);

 }
 
 static int request_frame(AVFilterLink *link)
 {

     AVFilterContext *ctx = link->src;

     ThumbContext *s = ctx->priv;

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

     if (ret == AVERROR_EOF && s->n) {
         ret = ff_filter_frame(link, get_best_frame(ctx));

         if (ret < 0)
             return ret;

         ret = AVERROR_EOF;
     }
     if (ret < 0)
         return ret;

     return 0;
 }
 

 static int config_props(AVFilterLink *inlink)
 {
     AVFilterContext *ctx = inlink->dst;

     ThumbContext *s = ctx->priv;

     s->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

     };

     AVFilterFormats *fmts_list = ff_make_format_list(pix_fmts);
     if (!fmts_list)
         return AVERROR(ENOMEM);
     return ff_set_common_formats(ctx, fmts_list);

 }
 

 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 ff_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,

 };