[FFmpeg-devel] [PATCH] lavfi: add thumb video filter.
Stefano Sabatini
stefasab at gmail.com
Sat Dec 24 11:39:44 CET 2011
On date Tuesday 2011-12-20 16:33:44 +0100, Clément Bœsch encoded:
> On Tue, Dec 20, 2011 at 03:11:13PM +0100, Stefano Sabatini wrote:
[...]
> Date: Mon, 24 Oct 2011 17:11:10 +0200
> Subject: [PATCH] lavfi: add thumbnail video filter.
>
> ---
> Changelog | 1 +
> doc/filters.texi | 20 ++++
> libavfilter/Makefile | 1 +
> libavfilter/allfilters.c | 1 +
> libavfilter/avfilter.h | 2 +-
> libavfilter/vf_thumbnail.c | 238 ++++++++++++++++++++++++++++++++++++++++++++
> 6 files changed, 262 insertions(+), 1 deletions(-)
> create mode 100644 libavfilter/vf_thumbnail.c
>
> diff --git a/Changelog b/Changelog
> index ad7fa8d..590752b 100644
> --- a/Changelog
> +++ b/Changelog
> @@ -139,6 +139,7 @@ easier to use. The changes are:
> - SBaGen (SBG) binaural beats script demuxer
> - OpenMG Audio muxer
> - Simple segmenting muxer
> +- Thumbnails support (see thumbnail video filter)
Nit++: I tend to prefer the simpler "thumbnail video filter", but then
it is just me
> version 0.8:
> diff --git a/doc/filters.texi b/doc/filters.texi
> index 699e0c1..37fd9cd 100644
> --- a/doc/filters.texi
> +++ b/doc/filters.texi
> @@ -2400,6 +2400,26 @@ For example:
> will create two separate outputs from the same input, one cropped and
> one padded.
>
> + at section thumbnail
> +Select the most representative frame in a given sequence of consecutive frames.
> +
> +It accepts as argument the frames batch size to analyze (default @var{N}=100);
> +in a set of @var{N} frames, the filter will pick one of them, and then handle
> +the next batch of @var{N} frames until the end.
> +
> +Since the filter keeps track of the whole frames sequence, a bigger @var{N}
> +value will result in a higher memory usage, so a high value is not recommended.
> +
> +The following example extract one picture each 50 frames:
> + at example
> +thumbnail=50
> + at end example
> +
> +Complete example of a thumbnail creation with @command{ffmpeg}:
> + at example
> +ffmpeg -i in.avi -vf thumbnail,scale=300:200 -frames:v 1 out.png
> + at end example
> +
> @section transpose
>
> Transpose rows with columns in the input video and optionally flip it.
> diff --git a/libavfilter/Makefile b/libavfilter/Makefile
> index a6fd18f..758ebc7 100644
> --- a/libavfilter/Makefile
> +++ b/libavfilter/Makefile
> @@ -78,6 +78,7 @@ OBJS-$(CONFIG_SETTB_FILTER) += vf_settb.o
> OBJS-$(CONFIG_SHOWINFO_FILTER) += vf_showinfo.o
> OBJS-$(CONFIG_SLICIFY_FILTER) += vf_slicify.o
> OBJS-$(CONFIG_SPLIT_FILTER) += vf_split.o
> +OBJS-$(CONFIG_THUMBNAIL_FILTER) += vf_thumbnail.o
> OBJS-$(CONFIG_TRANSPOSE_FILTER) += vf_transpose.o
> OBJS-$(CONFIG_UNSHARP_FILTER) += vf_unsharp.o
> OBJS-$(CONFIG_VFLIP_FILTER) += vf_vflip.o
> diff --git a/libavfilter/allfilters.c b/libavfilter/allfilters.c
> index fb50a3a..71b0381 100644
> --- a/libavfilter/allfilters.c
> +++ b/libavfilter/allfilters.c
> @@ -89,6 +89,7 @@ void avfilter_register_all(void)
> REGISTER_FILTER (SHOWINFO, showinfo, vf);
> REGISTER_FILTER (SLICIFY, slicify, vf);
> REGISTER_FILTER (SPLIT, split, vf);
> + REGISTER_FILTER (THUMBNAIL, thumbnail, vf);
> REGISTER_FILTER (TRANSPOSE, transpose, vf);
> REGISTER_FILTER (UNSHARP, unsharp, vf);
> REGISTER_FILTER (VFLIP, vflip, vf);
> diff --git a/libavfilter/avfilter.h b/libavfilter/avfilter.h
> index 4aceebd..c827458 100644
> --- a/libavfilter/avfilter.h
> +++ b/libavfilter/avfilter.h
> @@ -29,7 +29,7 @@
> #include "libavutil/rational.h"
>
> #define LIBAVFILTER_VERSION_MAJOR 2
> -#define LIBAVFILTER_VERSION_MINOR 53
> +#define LIBAVFILTER_VERSION_MINOR 54
> #define LIBAVFILTER_VERSION_MICRO 0
>
> #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \
> diff --git a/libavfilter/vf_thumbnail.c b/libavfilter/vf_thumbnail.c
> new file mode 100644
> index 0000000..462b114
> --- /dev/null
> +++ b/libavfilter/vf_thumbnail.c
> @@ -0,0 +1,238 @@
> +/*
> + * Copyright (c) 2011 Smartjog S.A.S, Clément Bœsch <clement.boesch at 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 at crocodile.org>.
> + * @url http://notbrainsurgery.livejournal.com/29773.html
> + */
> +
> +#include "avfilter.h"
> +
> +#define HIST_SIZE (3*256)
> +
> +struct thumb_frame {
> + AVFilterBufferRef *buf; ///< cached frame
> + int histogram[HIST_SIZE]; ///< RGB color distribution histogram of the frame
> +};
> +
> +typedef struct {
> + int n; ///< current frame
> + int n_frames; ///< number of frames for analysis
> + struct thumb_frame *frames; ///< the n_frames frames
> +} ThumbContext;
> +
> +static av_cold int init(AVFilterContext *ctx, const char *args, void *opaque)
> +{
> + ThumbContext *thumb = ctx->priv;
> +
> + if (args)
> + thumb->n_frames = strtol(args, NULL, 10);
> + if (thumb->n_frames < 2) {
why < 2?
> + thumb->n_frames = 100;
> + if (args)
> + av_log(ctx, AV_LOG_WARNING,
> + "Invalid number of frames specified, fallback to %d\n",
> + thumb->n_frames);
> + }
Also I don't like very well implicit behavior, for example with "foo"
this will result in warning and n=100, my opinion is that a
complain+fail approach is usually less painful as it is easy to miss a
warning.
The *tail in output from strtol should be checked, alternatively you
may use sscanf.
> + 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_INFO, "batch size: %d frames\n", thumb->n_frames);
> + return 0;
> +}
> +
> +static void draw_slice(AVFilterLink *inlink, int y, int h, int slice_dir)
> +{
> + int i, j;
> + AVFilterContext *ctx = inlink->dst;
> + ThumbContext *thumb = ctx->priv;
> + int *hist = thumb->frames[thumb->n].histogram;
> + AVFilterBufferRef *picref = inlink->cur_buf;
> + const uint8_t *p = picref->data[0] + y * picref->linesize[0];
> +
> + // update current frame RGB histogram
> + for (j = 0; j < 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 += picref->linesize[0];
> + }
> +}
> +
> +/**
> + * @brief compute Sum-square deviation to estimate "closeness"
nit++: @brief is almost never used
nit++: Compute sum-square ... final dot.
> + * @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 void end_frame(AVFilterLink *inlink)
> +{
> + int i, j, best_frame = 0;
Nit: best_frame -> best_frame_nb or idx (it's not a frame, it's an index)
> + double avg_hist[HIST_SIZE] = {0}, sq_err, min_sq_err = -1;
> + AVFilterLink *outlink = inlink->dst->outputs[0];
> + ThumbContext *thumb = inlink->dst->priv;
> + AVFilterContext *ctx = inlink->dst;
> +
> + // keep a reference of each frame
> + thumb->frames[thumb->n].buf = inlink->cur_buf;
> +
> + // no selection until the buffer of N frames is filled up
> + if (thumb->n < thumb->n_frames - 1) {
> + thumb->n++;
> + return;
> + }
> +
> + // average histogram of the N frames
> + for (j = 0; j < FF_ARRAY_ELEMS(avg_hist); j++) {
> + for (i = 0; i < thumb->n_frames; i++)
> + avg_hist[j] += (double)thumb->frames[i].histogram[j];
> + avg_hist[j] /= thumb->n_frames;
> + }
> +
> + // find the frame closer to the average using the sum of squared errors
> + for (i = 0; i < thumb->n_frames; i++) {
> + sq_err = frame_sum_square_err(thumb->frames[i].histogram, avg_hist);
> + if (i == 0 || sq_err < min_sq_err)
> + best_frame = i, min_sq_err = sq_err;
> + }
> +
> + // free and reset everything (except the best frame buffer)
> + for (i = 0; i < thumb->n_frames; i++) {
> + memset(thumb->frames[i].histogram, 0, sizeof(thumb->frames[i].histogram));
> + if (i == best_frame)
> + continue;
> + avfilter_unref_buffer(thumb->frames[i].buf);
> + thumb->frames[i].buf = NULL;
> + }
> + thumb->n = 0;
> +
> + // raise the chosen one
> + av_log(ctx, AV_LOG_INFO, "frame id #%d selected\n", best_frame);
maybe print also the PTS here
[...]
Looks fine otherwise.
--
FFmpeg = Funny and Free Muttering Practical Ecstatic Game
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