[FFmpeg-devel] [PATCH] lavfi: add thumb video filter.
Clément Bœsch
ubitux at gmail.com
Tue Dec 20 16:33:44 CET 2011
On Tue, Dec 20, 2011 at 03:11:13PM +0100, Stefano Sabatini wrote:
[...]
> > version 0.8:
> > diff --git a/doc/filters.texi b/doc/filters.texi
> > index 699e0c1..3f50ebf 100644
> > --- a/doc/filters.texi
> > +++ b/doc/filters.texi
> > @@ -2400,6 +2400,18 @@ For example:
> > will create two separate outputs from the same input, one cropped and
> > one padded.
> >
> > + at section thumbnail
> > +Select potential thumbnail frames.
>
> "thumbnail" is not a very clear term, maybe you could say "the most
> representative frame in a given sequence of consecutive frames".
>
Copy/pasted.
> > +
> > +It accepts as argument the threshold of frames to analyze (default is 100). The
> > +filter will pick one of these frames.
>
> Please give an explanation of the meaning of threshold, this is not
> clear at all from this description.
>
> From my reading of the code this filter reads N frames, and outputs
> the one whose histogram is nighest to the global average
> histogram. Maybe "batch_size" or "nb_frames" may be less confusing.
>
OK, see new attached version for a hopefully better wording.
> > A bigger value will result in a slower
> > +analysis and higher memory usage, but is likely to be more efficient.
>
> Again, if I understand the code the specified N will affect the number
> of output frames, because it changes the number of frames in each
> analyzed sequence, thus this statement looks quite misleading.
>
Also changed/simplified (just kept the memory usage chunk).
> > +
> > +Example of thumbnail creation:
> > + at example
> > +ffmpeg -i in.avi -vf thumbnail,scale=300:200 -frames:v 1 out.png
> > + at end example
>
> A pure libavfilter example also may be useful.
>
Added.
> [...]
> > diff --git a/libavfilter/vf_thumbnail.c b/libavfilter/vf_thumbnail.c
> > new file mode 100644
> > index 0000000..9be871e
> > --- /dev/null
> > +++ b/libavfilter/vf_thumbnail.c
> > @@ -0,0 +1,242 @@
> [...]
> > +/**
> > + * @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.
> > + *
> > + * Algorithm by Vadim Zaliva <lord at crocodile.org>.
> > + * @url http://notbrainsurgery.livejournal.com/29773.html
> > + */
> > +
>
> > +#include <math.h>
> > +#include "libavcodec/avcodec.h"
>
> why these?
>
Those and all the others below (except avfilter.h) where not needed
anymore, so dropped.
> > +#include "libavutil/imgutils.h"
> > +#include "libavutil/internal.h"
> > +#include "libswscale/swscale.h"
> > +#include "avfilter.h"
> > +
>
> > +#define HIST_SZ (3*256)
>
> Nit++: possibly HISTOGRAM_SIZE, or at least HIST_SIZE
>
renamed to HIST_SIZE
> > +#define DEF_FRAMES_THRESHOLD 100
> > +
> > +struct thumb_frame {
> > + AVFilterBufferRef *buf; ///< cached frame
> > + int histogram[HIST_SZ]; ///< RGB color distribution histogram of the frame
> > +};
> > +
> > +typedef struct {
> > + int n; ///< current frame
> > + int n_frames; ///< threshold 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) {
> > + if (args)
>
> > + av_log(ctx, AV_LOG_WARNING,
> > + "Invalid frame threshold specified, fallback to "
> > + AV_STRINGIFY(DEF_FRAMES_THRESHOLD) "\n");
>
> uh? why not a simple %d?
>
Indeed…
> > + thumb->n_frames = DEF_FRAMES_THRESHOLD;
> > + }
> > + 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 frames threshold\n");
> > + return AVERROR(ENOMEM);
> > + }
>
> > + av_log(ctx, AV_LOG_INFO, "Select thumbnail with threshold of %d frames\n",
> > + thumb->n_frames);
>
> simpler/less cluttered: threshold:%d
>
Changed into "batch size: %d 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 Root-mean-square deviation to estimate "closeness"
> > + * @param hist color distribution histogram
> > + * @param median average color distribution histogram
> > + * @return root mean squared error
> > + */
>
> > +static float frame_rmse(const int *hist, const float *median)
> > +{
> > + int i;
> > + float err, mean_sq_err = 0;
> > + for (i = 0; i < HIST_SZ; i++) {
> > + err = median[i] - (float)hist[i];
> > + mean_sq_err += err*err / HIST_SZ;
> > + }
>
> you can factor out the division, and gain speed (and precision)
>
Messing with filters drive me away from the algo implementation; obviously
this can be improved. More than than this factoring out: since we are in
the situation where we need to evaluate sqrt(a/K) ≤ sqrt(b/K) I simplified
to a ≤ b... Root mean square deviation → sum square deviation.
Also, since the value can get somewhat big, I also changed the type from
float to double.
> > + return sqrtf(mean_sq_err);
> > +}
> > +
> > +static void end_frame(AVFilterLink *inlink)
> > +{
> > + int i, j, best_frame = 0;
>
> > + float avg[HIST_SZ] = {0}, rmse, min_rmse = -1;
>
> avg -> please more meaningful name, or use it in a local scope
>
The first usage of avg is under the comment "average histogram of the N
frames" so I thought it was obvious. Also the HIST_SIZE gives a hint.
Anyway, renamed to avg_hist.
> > + 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); j++)
> > + for (i = 0; i < thumb->n_frames; i++)
>
> > + avg[j] += (float)thumb->frames[i].histogram[j] / thumb->n_frames;
>
> again, you can factor out the division
>
done.
> > + // find the frame closer to the average using RMSE
> > + for (i = 0; i < thumb->n_frames; i++) {
> > + rmse = frame_rmse(thumb->frames[i].histogram, avg);
> > + if (i == 0 || rmse < min_rmse)
> > + best_frame = i, min_rmse = rmse;
> > + }
> > +
> > + // 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));
>
> is this required?
>
Yes, the frames are not reallocated, and the histogram are re-used between
sequences analysis.
[...]
> > +static int query_formats(AVFilterContext *ctx)
> > +{
> > + static const enum PixelFormat pix_fmts[] = {
> > + PIX_FMT_RGB24, PIX_FMT_BGR24,
> > + PIX_FMT_NONE
> > + };
> > + avfilter_set_common_pixel_formats(ctx, avfilter_make_format_list(pix_fmts));
> > + return 0;
>
> note: this can be easily extended to support more pixel formats
>
Maybe, I just implemented the basic algorithm without much thinking.
> > +}
> > +
> > +AVFilter avfilter_vf_thumbnail = {
> > + .name = "thumbnail",
>
> > + .description = NULL_IF_CONFIG_SMALL("Thumbnail selection filter"),
>
> Nit: description is a complete sentence describing what the filter
> *does*, rather than a long name.
I shamely copy/pasted again your suggestion at the beginning of your
review.
New patch attached, thanks.
--
Clément B.
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From 1687ae3140f74b4481332ce8b3225d9bf0d9e655 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Cl=C3=A9ment=20B=C5=93sch?= <clement.boesch at smartjog.com>
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)
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) {
+ thumb->n_frames = 100;
+ if (args)
+ av_log(ctx, AV_LOG_WARNING,
+ "Invalid number of frames specified, fallback to %d\n",
+ thumb->n_frames);
+ }
+ 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"
+ * @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;
+ 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);
+ avfilter_start_frame(outlink, thumb->frames[best_frame].buf);
+ thumb->frames[best_frame].buf = NULL;
+ avfilter_draw_slice(outlink, 0, inlink->h, 1);
+ avfilter_end_frame(outlink);
+}
+
+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++) {
+ avfilter_unref_buffer(thumb->frames[i].buf);
+ thumb->frames[i].buf = NULL;
+ }
+ av_freep(&thumb->frames);
+}
+
+static void null_start_frame(AVFilterLink *link, AVFilterBufferRef *picref) { }
+
+static int request_frame(AVFilterLink *link)
+{
+ ThumbContext *thumb = link->src->priv;
+
+ /* loop until a frame thumbnail is available (when a frame is queued,
+ * thumb->n is reset to zero) */
+ while (thumb->n) {
+ int ret = avfilter_request_frame(link->src->inputs[0]);
+ if (ret < 0)
+ return ret;
+ }
+ return 0;
+}
+
+static int poll_frame(AVFilterLink *link)
+{
+ ThumbContext *thumb = link->src->priv;
+ AVFilterLink *inlink = link->src->inputs[0];
+ int ret, available_frames = avfilter_poll_frame(inlink);
+
+ /* If the input link is not able to provide any frame, we can't do anything
+ * at the moment and thus have zero thumbnail available. */
+ if (!available_frames)
+ return 0;
+
+ /* Since at least one frame is available and the next frame will allow us
+ * to compute a thumbnail, we can return 1 frame. */
+ if (thumb->n == thumb->n_frames - 1)
+ return 1;
+
+ /* we have some frame(s) available in the input link, but not yet enough to
+ * output a thumbnail, so we request more */
+ ret = avfilter_request_frame(inlink);
+ return ret < 0 ? ret : 0;
+}
+
+static int query_formats(AVFilterContext *ctx)
+{
+ static const enum PixelFormat pix_fmts[] = {
+ PIX_FMT_RGB24, PIX_FMT_BGR24,
+ PIX_FMT_NONE
+ };
+ avfilter_set_common_pixel_formats(ctx, avfilter_make_format_list(pix_fmts));
+ return 0;
+}
+
+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 = (const AVFilterPad[]) {
+ { .name = "default",
+ .type = AVMEDIA_TYPE_VIDEO,
+ .get_video_buffer = avfilter_null_get_video_buffer,
+ .start_frame = null_start_frame,
+ .draw_slice = draw_slice,
+ .end_frame = end_frame,
+ },{ .name = NULL }
+ },
+ .outputs = (const AVFilterPad[]) {
+ { .name = "default",
+ .type = AVMEDIA_TYPE_VIDEO,
+ .request_frame = request_frame,
+ .poll_frame = poll_frame,
+ .rej_perms = AV_PERM_REUSE2,
+ },{ .name = NULL }
+ },
+};
--
1.7.7.3
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