mirror of
https://github.com/FFmpeg/FFmpeg.git
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236 lines
7.4 KiB
C
236 lines
7.4 KiB
C
/*
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* Copyright (c) 2011 Smartjog S.A.S, Clément Bœsch <clement.boesch@smartjog.com>
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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/**
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* @file
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* Potential thumbnail lookup filter to reduce the risk of an inappropriate
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* selection (such as a black frame) we could get with an absolute seek.
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*
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* Simplified version of algorithm by Vadim Zaliva <lord@crocodile.org>.
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* @see http://notbrainsurgery.livejournal.com/29773.html
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*/
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#include "avfilter.h"
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#include "internal.h"
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#define HIST_SIZE (3*256)
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struct thumb_frame {
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AVFilterBufferRef *buf; ///< cached frame
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int histogram[HIST_SIZE]; ///< RGB color distribution histogram of the frame
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};
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typedef struct {
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int n; ///< current frame
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int n_frames; ///< number of frames for analysis
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struct thumb_frame *frames; ///< the n_frames frames
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} ThumbContext;
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static av_cold int init(AVFilterContext *ctx, const char *args)
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{
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ThumbContext *thumb = ctx->priv;
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if (!args) {
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thumb->n_frames = 100;
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} else {
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int n = sscanf(args, "%d", &thumb->n_frames);
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if (n != 1 || thumb->n_frames < 2) {
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thumb->n_frames = 0;
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av_log(ctx, AV_LOG_ERROR,
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"Invalid number of frames specified (minimum is 2).\n");
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return AVERROR(EINVAL);
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}
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}
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thumb->frames = av_calloc(thumb->n_frames, sizeof(*thumb->frames));
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if (!thumb->frames) {
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av_log(ctx, AV_LOG_ERROR,
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"Allocation failure, try to lower the number of frames\n");
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return AVERROR(ENOMEM);
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}
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av_log(ctx, AV_LOG_VERBOSE, "batch size: %d frames\n", thumb->n_frames);
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return 0;
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}
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/**
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* @brief Compute Sum-square deviation to estimate "closeness".
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* @param hist color distribution histogram
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* @param median average color distribution histogram
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* @return sum of squared errors
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*/
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static double frame_sum_square_err(const int *hist, const double *median)
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{
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int i;
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double err, sum_sq_err = 0;
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for (i = 0; i < HIST_SIZE; i++) {
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err = median[i] - (double)hist[i];
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sum_sq_err += err*err;
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}
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return sum_sq_err;
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}
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static int filter_frame(AVFilterLink *inlink, AVFilterBufferRef *frame)
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{
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int i, j, best_frame_idx = 0;
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double avg_hist[HIST_SIZE] = {0}, sq_err, min_sq_err = -1;
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AVFilterContext *ctx = inlink->dst;
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ThumbContext *thumb = ctx->priv;
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AVFilterLink *outlink = ctx->outputs[0];
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AVFilterBufferRef *picref;
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int *hist = thumb->frames[thumb->n].histogram;
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const uint8_t *p = frame->data[0];
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// keep a reference of each frame
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thumb->frames[thumb->n].buf = frame;
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// update current frame RGB histogram
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for (j = 0; j < inlink->h; j++) {
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for (i = 0; i < inlink->w; i++) {
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hist[0*256 + p[i*3 ]]++;
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hist[1*256 + p[i*3 + 1]]++;
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hist[2*256 + p[i*3 + 2]]++;
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}
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p += frame->linesize[0];
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}
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// no selection until the buffer of N frames is filled up
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if (thumb->n < thumb->n_frames - 1) {
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thumb->n++;
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return 0;
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}
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// average histogram of the N frames
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for (j = 0; j < FF_ARRAY_ELEMS(avg_hist); j++) {
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for (i = 0; i < thumb->n_frames; i++)
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avg_hist[j] += (double)thumb->frames[i].histogram[j];
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avg_hist[j] /= thumb->n_frames;
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}
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// find the frame closer to the average using the sum of squared errors
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for (i = 0; i < thumb->n_frames; i++) {
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sq_err = frame_sum_square_err(thumb->frames[i].histogram, avg_hist);
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if (i == 0 || sq_err < min_sq_err)
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best_frame_idx = i, min_sq_err = sq_err;
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}
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// free and reset everything (except the best frame buffer)
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for (i = 0; i < thumb->n_frames; i++) {
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memset(thumb->frames[i].histogram, 0, sizeof(thumb->frames[i].histogram));
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if (i == best_frame_idx)
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continue;
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avfilter_unref_bufferp(&thumb->frames[i].buf);
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}
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thumb->n = 0;
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// raise the chosen one
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picref = thumb->frames[best_frame_idx].buf;
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av_log(ctx, AV_LOG_INFO, "frame id #%d (pts_time=%f) selected\n",
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best_frame_idx, picref->pts * av_q2d(inlink->time_base));
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thumb->frames[best_frame_idx].buf = NULL;
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return ff_filter_frame(outlink, picref);
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}
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static av_cold void uninit(AVFilterContext *ctx)
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{
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int i;
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ThumbContext *thumb = ctx->priv;
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for (i = 0; i < thumb->n_frames && thumb->frames[i].buf; i++)
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avfilter_unref_bufferp(&thumb->frames[i].buf);
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av_freep(&thumb->frames);
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}
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static int request_frame(AVFilterLink *link)
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{
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ThumbContext *thumb = link->src->priv;
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/* loop until a frame thumbnail is available (when a frame is queued,
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* thumb->n is reset to zero) */
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do {
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int ret = ff_request_frame(link->src->inputs[0]);
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if (ret < 0)
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return ret;
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} while (thumb->n);
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return 0;
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}
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static int poll_frame(AVFilterLink *link)
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{
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ThumbContext *thumb = link->src->priv;
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AVFilterLink *inlink = link->src->inputs[0];
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int ret, available_frames = ff_poll_frame(inlink);
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/* If the input link is not able to provide any frame, we can't do anything
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* at the moment and thus have zero thumbnail available. */
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if (!available_frames)
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return 0;
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/* Since at least one frame is available and the next frame will allow us
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* to compute a thumbnail, we can return 1 frame. */
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if (thumb->n == thumb->n_frames - 1)
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return 1;
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/* we have some frame(s) available in the input link, but not yet enough to
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* output a thumbnail, so we request more */
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ret = ff_request_frame(inlink);
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return ret < 0 ? ret : 0;
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}
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static int query_formats(AVFilterContext *ctx)
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{
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static const enum AVPixelFormat pix_fmts[] = {
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AV_PIX_FMT_RGB24, AV_PIX_FMT_BGR24,
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AV_PIX_FMT_NONE
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};
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ff_set_common_formats(ctx, ff_make_format_list(pix_fmts));
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return 0;
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}
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static const AVFilterPad thumbnail_inputs[] = {
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{
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.name = "default",
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.type = AVMEDIA_TYPE_VIDEO,
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.get_video_buffer = ff_null_get_video_buffer,
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.min_perms = AV_PERM_PRESERVE,
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.filter_frame = filter_frame,
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},
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{ NULL }
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};
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static const AVFilterPad thumbnail_outputs[] = {
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{
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.name = "default",
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.type = AVMEDIA_TYPE_VIDEO,
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.request_frame = request_frame,
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.poll_frame = poll_frame,
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},
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{ NULL }
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};
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AVFilter avfilter_vf_thumbnail = {
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.name = "thumbnail",
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.description = NULL_IF_CONFIG_SMALL("Select the most representative frame in a given sequence of consecutive frames."),
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.priv_size = sizeof(ThumbContext),
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.init = init,
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.uninit = uninit,
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.query_formats = query_formats,
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.inputs = thumbnail_inputs,
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.outputs = thumbnail_outputs,
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};
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