/*
* 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 {
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,
};