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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 "avfilter.h"
31 #include "internal.h"
32 
33 #define HIST_SIZE (3*256)
34 
35 struct thumb_frame {
36  AVFilterBufferRef *buf; ///< cached frame
37  int histogram[HIST_SIZE]; ///< RGB color distribution histogram of the frame
38 };
39 
40 typedef struct {
41  int n; ///< current frame
42  int n_frames; ///< number of frames for analysis
43  struct thumb_frame *frames; ///< the n_frames frames
44 } ThumbContext;
45 
46 static av_cold int init(AVFilterContext *ctx, const char *args)
47 {
48  ThumbContext *thumb = ctx->priv;
49 
50  if (!args) {
51  thumb->n_frames = 100;
52  } else {
53  int n = sscanf(args, "%d", &thumb->n_frames);
54  if (n != 1 || thumb->n_frames < 2) {
55  thumb->n_frames = 0;
56  av_log(ctx, AV_LOG_ERROR,
57  "Invalid number of frames specified (minimum is 2).\n");
58  return AVERROR(EINVAL);
59  }
60  }
61  thumb->frames = av_calloc(thumb->n_frames, sizeof(*thumb->frames));
62  if (!thumb->frames) {
63  av_log(ctx, AV_LOG_ERROR,
64  "Allocation failure, try to lower the number of frames\n");
65  return AVERROR(ENOMEM);
66  }
67  av_log(ctx, AV_LOG_VERBOSE, "batch size: %d frames\n", thumb->n_frames);
68  return 0;
69 }
70 
71 /**
72  * @brief Compute Sum-square deviation to estimate "closeness".
73  * @param hist color distribution histogram
74  * @param median average color distribution histogram
75  * @return sum of squared errors
76  */
77 static double frame_sum_square_err(const int *hist, const double *median)
78 {
79  int i;
80  double err, sum_sq_err = 0;
81 
82  for (i = 0; i < HIST_SIZE; i++) {
83  err = median[i] - (double)hist[i];
84  sum_sq_err += err*err;
85  }
86  return sum_sq_err;
87 }
88 
90 {
91  int i, j, best_frame_idx = 0;
92  double avg_hist[HIST_SIZE] = {0}, sq_err, min_sq_err = -1;
93  AVFilterContext *ctx = inlink->dst;
94  ThumbContext *thumb = ctx->priv;
95  AVFilterLink *outlink = ctx->outputs[0];
96  AVFilterBufferRef *picref;
97  int *hist = thumb->frames[thumb->n].histogram;
98  const uint8_t *p = frame->data[0];
99 
100  // keep a reference of each frame
101  thumb->frames[thumb->n].buf = frame;
102 
103  // update current frame RGB histogram
104  for (j = 0; j < inlink->h; j++) {
105  for (i = 0; i < inlink->w; i++) {
106  hist[0*256 + p[i*3 ]]++;
107  hist[1*256 + p[i*3 + 1]]++;
108  hist[2*256 + p[i*3 + 2]]++;
109  }
110  p += frame->linesize[0];
111  }
112 
113  // no selection until the buffer of N frames is filled up
114  if (thumb->n < thumb->n_frames - 1) {
115  thumb->n++;
116  return 0;
117  }
118 
119  // average histogram of the N frames
120  for (j = 0; j < FF_ARRAY_ELEMS(avg_hist); j++) {
121  for (i = 0; i < thumb->n_frames; i++)
122  avg_hist[j] += (double)thumb->frames[i].histogram[j];
123  avg_hist[j] /= thumb->n_frames;
124  }
125 
126  // find the frame closer to the average using the sum of squared errors
127  for (i = 0; i < thumb->n_frames; i++) {
128  sq_err = frame_sum_square_err(thumb->frames[i].histogram, avg_hist);
129  if (i == 0 || sq_err < min_sq_err)
130  best_frame_idx = i, min_sq_err = sq_err;
131  }
132 
133  // free and reset everything (except the best frame buffer)
134  for (i = 0; i < thumb->n_frames; i++) {
135  memset(thumb->frames[i].histogram, 0, sizeof(thumb->frames[i].histogram));
136  if (i == best_frame_idx)
137  continue;
138  avfilter_unref_bufferp(&thumb->frames[i].buf);
139  }
140  thumb->n = 0;
141 
142  // raise the chosen one
143  picref = thumb->frames[best_frame_idx].buf;
144  av_log(ctx, AV_LOG_INFO, "frame id #%d (pts_time=%f) selected\n",
145  best_frame_idx, picref->pts * av_q2d(inlink->time_base));
146  thumb->frames[best_frame_idx].buf = NULL;
147  return ff_filter_frame(outlink, picref);
148 }
149 
150 static av_cold void uninit(AVFilterContext *ctx)
151 {
152  int i;
153  ThumbContext *thumb = ctx->priv;
154  for (i = 0; i < thumb->n_frames && thumb->frames[i].buf; i++)
155  avfilter_unref_bufferp(&thumb->frames[i].buf);
156  av_freep(&thumb->frames);
157 }
158 
159 static int request_frame(AVFilterLink *link)
160 {
161  ThumbContext *thumb = link->src->priv;
162 
163  /* loop until a frame thumbnail is available (when a frame is queued,
164  * thumb->n is reset to zero) */
165  do {
166  int ret = ff_request_frame(link->src->inputs[0]);
167  if (ret < 0)
168  return ret;
169  } while (thumb->n);
170  return 0;
171 }
172 
173 static int poll_frame(AVFilterLink *link)
174 {
175  ThumbContext *thumb = link->src->priv;
176  AVFilterLink *inlink = link->src->inputs[0];
177  int ret, available_frames = ff_poll_frame(inlink);
178 
179  /* If the input link is not able to provide any frame, we can't do anything
180  * at the moment and thus have zero thumbnail available. */
181  if (!available_frames)
182  return 0;
183 
184  /* Since at least one frame is available and the next frame will allow us
185  * to compute a thumbnail, we can return 1 frame. */
186  if (thumb->n == thumb->n_frames - 1)
187  return 1;
188 
189  /* we have some frame(s) available in the input link, but not yet enough to
190  * output a thumbnail, so we request more */
191  ret = ff_request_frame(inlink);
192  return ret < 0 ? ret : 0;
193 }
194 
196 {
197  static const enum AVPixelFormat pix_fmts[] = {
200  };
202  return 0;
203 }
204 
205 static const AVFilterPad thumbnail_inputs[] = {
206  {
207  .name = "default",
208  .type = AVMEDIA_TYPE_VIDEO,
209  .get_video_buffer = ff_null_get_video_buffer,
210  .min_perms = AV_PERM_PRESERVE,
211  .filter_frame = filter_frame,
212  },
213  { NULL }
214 };
215 
216 static const AVFilterPad thumbnail_outputs[] = {
217  {
218  .name = "default",
219  .type = AVMEDIA_TYPE_VIDEO,
220  .request_frame = request_frame,
221  .poll_frame = poll_frame,
222  },
223  { NULL }
224 };
225 
227  .name = "thumbnail",
228  .description = NULL_IF_CONFIG_SMALL("Select the most representative frame in a given sequence of consecutive frames."),
229  .priv_size = sizeof(ThumbContext),
230  .init = init,
231  .uninit = uninit,
233  .inputs = thumbnail_inputs,
234  .outputs = thumbnail_outputs,
235 };