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vf_thumbnail.c
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1 /*
2  * Copyright (c) 2011 Smartjog S.A.S, Clément Bœsch <clement.boesch@smartjog.com>
3  *
4  * This file is part of FFmpeg.
5  *
6  * FFmpeg is free software; you can redistribute it and/or
7  * modify it under the terms of the GNU Lesser General Public
8  * License as published by the Free Software Foundation; either
9  * version 2.1 of the License, or (at your option) any later version.
10  *
11  * FFmpeg is distributed in the hope that it will be useful,
12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14  * Lesser General Public License for more details.
15  *
16  * You should have received a copy of the GNU Lesser General Public
17  * License along with FFmpeg; if not, write to the Free Software
18  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
19  */
20 
21 /**
22  * @file
23  * Potential thumbnail lookup filter to reduce the risk of an inappropriate
24  * selection (such as a black frame) we could get with an absolute seek.
25  *
26  * Simplified version of algorithm by Vadim Zaliva <lord@crocodile.org>.
27  * @see http://notbrainsurgery.livejournal.com/29773.html
28  */
29 
30 #include "libavutil/opt.h"
31 #include "avfilter.h"
32 #include "internal.h"
33 
34 #define HIST_SIZE (3*256)
35 
36 struct thumb_frame {
37  AVFrame *buf; ///< cached frame
38  int histogram[HIST_SIZE]; ///< RGB color distribution histogram of the frame
39 };
40 
41 typedef struct {
42  const AVClass *class;
43  int n; ///< current frame
44  int n_frames; ///< number of frames for analysis
45  struct thumb_frame *frames; ///< the n_frames frames
46  AVRational tb; ///< copy of the input timebase to ease access
47 } ThumbContext;
48 
49 #define OFFSET(x) offsetof(ThumbContext, x)
50 #define FLAGS AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_FILTERING_PARAM
51 
52 static const AVOption thumbnail_options[] = {
53  { "n", "set the frames batch size", OFFSET(n_frames), AV_OPT_TYPE_INT, {.i64=100}, 2, INT_MAX, FLAGS },
54  { NULL }
55 };
56 
57 AVFILTER_DEFINE_CLASS(thumbnail);
58 
59 static av_cold int init(AVFilterContext *ctx)
60 {
61  ThumbContext *thumb = ctx->priv;
62 
63  thumb->frames = av_calloc(thumb->n_frames, sizeof(*thumb->frames));
64  if (!thumb->frames) {
65  av_log(ctx, AV_LOG_ERROR,
66  "Allocation failure, try to lower the number of frames\n");
67  return AVERROR(ENOMEM);
68  }
69  av_log(ctx, AV_LOG_VERBOSE, "batch size: %d frames\n", thumb->n_frames);
70  return 0;
71 }
72 
73 /**
74  * @brief Compute Sum-square deviation to estimate "closeness".
75  * @param hist color distribution histogram
76  * @param median average color distribution histogram
77  * @return sum of squared errors
78  */
79 static double frame_sum_square_err(const int *hist, const double *median)
80 {
81  int i;
82  double err, sum_sq_err = 0;
83 
84  for (i = 0; i < HIST_SIZE; i++) {
85  err = median[i] - (double)hist[i];
86  sum_sq_err += err*err;
87  }
88  return sum_sq_err;
89 }
90 
92 {
93  AVFrame *picref;
94  ThumbContext *thumb = ctx->priv;
95  int i, j, best_frame_idx = 0;
96  int nb_frames = thumb->n;
97  double avg_hist[HIST_SIZE] = {0}, sq_err, min_sq_err = -1;
98 
99  // average histogram of the N frames
100  for (j = 0; j < FF_ARRAY_ELEMS(avg_hist); j++) {
101  for (i = 0; i < nb_frames; i++)
102  avg_hist[j] += (double)thumb->frames[i].histogram[j];
103  avg_hist[j] /= nb_frames;
104  }
105 
106  // find the frame closer to the average using the sum of squared errors
107  for (i = 0; i < nb_frames; i++) {
108  sq_err = frame_sum_square_err(thumb->frames[i].histogram, avg_hist);
109  if (i == 0 || sq_err < min_sq_err)
110  best_frame_idx = i, min_sq_err = sq_err;
111  }
112 
113  // free and reset everything (except the best frame buffer)
114  for (i = 0; i < nb_frames; i++) {
115  memset(thumb->frames[i].histogram, 0, sizeof(thumb->frames[i].histogram));
116  if (i != best_frame_idx)
117  av_frame_free(&thumb->frames[i].buf);
118  }
119  thumb->n = 0;
120 
121  // raise the chosen one
122  picref = thumb->frames[best_frame_idx].buf;
123  av_log(ctx, AV_LOG_INFO, "frame id #%d (pts_time=%f) selected "
124  "from a set of %d images\n", best_frame_idx,
125  picref->pts * av_q2d(thumb->tb), nb_frames);
126  thumb->frames[best_frame_idx].buf = NULL;
127 
128  return picref;
129 }
130 
131 static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
132 {
133  int i, j;
134  AVFilterContext *ctx = inlink->dst;
135  ThumbContext *thumb = ctx->priv;
136  AVFilterLink *outlink = ctx->outputs[0];
137  int *hist = thumb->frames[thumb->n].histogram;
138  const uint8_t *p = frame->data[0];
139 
140  // keep a reference of each frame
141  thumb->frames[thumb->n].buf = frame;
142 
143  // update current frame RGB histogram
144  for (j = 0; j < inlink->h; j++) {
145  for (i = 0; i < inlink->w; i++) {
146  hist[0*256 + p[i*3 ]]++;
147  hist[1*256 + p[i*3 + 1]]++;
148  hist[2*256 + p[i*3 + 2]]++;
149  }
150  p += frame->linesize[0];
151  }
152 
153  // no selection until the buffer of N frames is filled up
154  thumb->n++;
155  if (thumb->n < thumb->n_frames)
156  return 0;
157 
158  return ff_filter_frame(outlink, get_best_frame(ctx));
159 }
160 
161 static av_cold void uninit(AVFilterContext *ctx)
162 {
163  int i;
164  ThumbContext *thumb = ctx->priv;
165  for (i = 0; i < thumb->n_frames && thumb->frames[i].buf; i++)
166  av_frame_free(&thumb->frames[i].buf);
167  av_freep(&thumb->frames);
168 }
169 
170 static int request_frame(AVFilterLink *link)
171 {
172  AVFilterContext *ctx = link->src;
173  ThumbContext *thumb = ctx->priv;
174 
175  /* loop until a frame thumbnail is available (when a frame is queued,
176  * thumb->n is reset to zero) */
177  do {
178  int ret = ff_request_frame(ctx->inputs[0]);
179  if (ret == AVERROR_EOF && thumb->n) {
180  ret = ff_filter_frame(link, get_best_frame(ctx));
181  if (ret < 0)
182  return ret;
183  ret = AVERROR_EOF;
184  }
185  if (ret < 0)
186  return ret;
187  } while (thumb->n);
188  return 0;
189 }
190 
191 static int config_props(AVFilterLink *inlink)
192 {
193  AVFilterContext *ctx = inlink->dst;
194  ThumbContext *thumb = ctx->priv;
195 
196  thumb->tb = inlink->time_base;
197  return 0;
198 }
199 
201 {
202  static const enum AVPixelFormat pix_fmts[] = {
205  };
207  return 0;
208 }
209 
210 static const AVFilterPad thumbnail_inputs[] = {
211  {
212  .name = "default",
213  .type = AVMEDIA_TYPE_VIDEO,
214  .config_props = config_props,
215  .filter_frame = filter_frame,
216  },
217  { NULL }
218 };
219 
220 static const AVFilterPad thumbnail_outputs[] = {
221  {
222  .name = "default",
223  .type = AVMEDIA_TYPE_VIDEO,
224  .request_frame = request_frame,
225  },
226  { NULL }
227 };
228 
230  .name = "thumbnail",
231  .description = NULL_IF_CONFIG_SMALL("Select the most representative frame in a given sequence of consecutive frames."),
232  .priv_size = sizeof(ThumbContext),
233  .init = init,
234  .uninit = uninit,
236  .inputs = thumbnail_inputs,
237  .outputs = thumbnail_outputs,
238  .priv_class = &thumbnail_class,
239 };