[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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