lavfi: add blackdetect filter

Address trac ticket #901.

Changelog

@@ -11,6 +11,7 @@ version next:
 - ID3v2 attached pictures reading and writing
 - WMA Lossless decoder
 - bluray protocol
+- blackdetect filter
 
 
 version 0.10:

doc/filters.texi

@@ -761,6 +761,60 @@ video, use the command:
 ass=sub.ass
 @end example
 
+@section blackdetect
+
+Detect video intervals that are (almost) completely black. Can be
+useful to detect chapter transitions, commercials, or invalid
+recordings. Output lines contains the time for the start, end and
+duration of the detected black interval expressed in seconds.
+
+In order to display the output lines, you need to set the loglevel at
+least to the AV_LOG_INFO value.
+
+This filter accepts a list of options in the form of
+@var{key}=@var{value} pairs separated by ":". A description of the
+accepted options follows.
+
+@table @option
+@item black_min_duration, d
+Set the minimum detected black duration expressed in seconds. It must
+be a non-negative floating point number.
+
+Default value is 2.0.
+
+@item picture_black_ratio_th, pic_th
+Set the threshold for considering a picture "black".
+Express the minimum value for the ratio:
+@example
+@var{nb_black_pixels} / @var{nb_pixels}
+@end example
+
+for which a picture is considered black.
+Default value is 0.98.
+
+@item pixel_black_th, pix_th
+Set the threshold for considering a pixel "black".
+
+The threshold expresses the maximum pixel luminance value for which a
+pixel is considered "black". The provided value is scaled according to
+the following equation:
+@example
+@var{absolute_threshold} = @var{luminance_minimum_value} + @var{pixel_black_th} * @var{luminance_range_size}
+@end example
+
+@var{luminance_range_size} and @var{luminance_minimum_value} depend on
+the input video format, the range is [0-255] for YUV full-range
+formats and [16-235] for YUV non full-range formats.
+
+Default value is 0.10.
+@end table
+
+The following example sets the maximum pixel threshold to the minimum
+value, and detects only black intervals of 2 or more seconds:
+@example
+blackdetect=d=2:pix_th=0.00
+@end example
+
 @section blackframe
 
 Detect frames that are (almost) completely black. Can be useful to

libavfilter/Makefile

@@ -48,6 +48,7 @@ OBJS-$(CONFIG_ABUFFERSINK_FILTER)            += sink_buffer.o
 OBJS-$(CONFIG_ANULLSINK_FILTER)              += asink_anullsink.o
 
 OBJS-$(CONFIG_ASS_FILTER)                    += vf_ass.o
+OBJS-$(CONFIG_BLACKDETECT_FILTER)            += vf_blackdetect.o
 OBJS-$(CONFIG_BLACKFRAME_FILTER)             += vf_blackframe.o
 OBJS-$(CONFIG_BOXBLUR_FILTER)                += vf_boxblur.o
 OBJS-$(CONFIG_COPY_FILTER)                   += vf_copy.o

libavfilter/allfilters.c

@@ -56,6 +56,7 @@ void avfilter_register_all(void)
     REGISTER_FILTER (ANULLSINK,   anullsink,   asink);
 
     REGISTER_FILTER (ASS,         ass,  vf);
+    REGISTER_FILTER (BLACKDETECT, blackdetect, vf);
     REGISTER_FILTER (BLACKFRAME,  blackframe,  vf);
     REGISTER_FILTER (BOXBLUR,     boxblur,     vf);
     REGISTER_FILTER (COPY,        copy,        vf);

libavfilter/version.h

@@ -29,8 +29,8 @@
 #include "libavutil/avutil.h"
 
 #define LIBAVFILTER_VERSION_MAJOR  2
-#define LIBAVFILTER_VERSION_MINOR 62
+#define LIBAVFILTER_VERSION_MINOR 63
-#define LIBAVFILTER_VERSION_MICRO 101
+#define LIBAVFILTER_VERSION_MICRO 100
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \
                                                LIBAVFILTER_VERSION_MINOR, \

libavfilter/vf_blackdetect.c

@@ -0,0 +1,209 @@
+/*
+ * Copyright (c) 2012 Stefano Sabatini
+ *
+ * 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
+ * Video black detector, loosely based on blackframe with extended
+ * syntax and features
+ */
+
+#include <float.h>
+#include "libavutil/opt.h"
+#include "libavutil/timestamp.h"
+#include "avfilter.h"
+#include "internal.h"
+
+typedef struct {
+    const AVClass *class;
+    double  black_min_duration_time; ///< minimum duration of detected black, in seconds
+    int64_t black_min_duration;      ///< minimum duration of detected black, expressed in timebase units
+    int64_t black_start;             ///< pts start time of the first black picture
+    int64_t black_end;               ///< pts end time of the last black picture
+    int black_started;
+
+    double       picture_black_ratio_th;
+    double       pixel_black_th;
+    unsigned int pixel_black_th_i;
+
+    unsigned int frame_count;       ///< frame number
+    unsigned int nb_black_pixels;   ///< number of black pixels counted so far
+} BlackDetectContext;
+
+#define OFFSET(x) offsetof(BlackDetectContext, x)
+static const AVOption blackdetect_options[] = {
+    { "d",                  "set minimum detected black duration in seconds", OFFSET(black_min_duration_time), AV_OPT_TYPE_DOUBLE, {.dbl=2}, 0, DBL_MAX},
+    { "black_min_duration", "set minimum detected black duration in seconds", OFFSET(black_min_duration_time), AV_OPT_TYPE_DOUBLE, {.dbl=2}, 0, DBL_MAX},
+    { "picture_black_ratio_th", "set the picture black ratio threshold", OFFSET(picture_black_ratio_th), AV_OPT_TYPE_DOUBLE, {.dbl=.98}, 0, 1},
+    { "pic_th",                 "set the picture black ratio threshold", OFFSET(picture_black_ratio_th), AV_OPT_TYPE_DOUBLE, {.dbl=.98}, 0, 1},
+    { "pixel_black_th", "set the pixel black threshold", OFFSET(pixel_black_th), AV_OPT_TYPE_DOUBLE, {.dbl=.10}, 0, 1},
+    { "pix_th",         "set the pixel black threshold", OFFSET(pixel_black_th), AV_OPT_TYPE_DOUBLE, {.dbl=.10}, 0, 1},
+    { NULL },
+};
+
+static const char *blackdetect_get_name(void *ctx)
+{
+    return "blackdetect";
+}
+
+static const AVClass blackdetect_class = {
+    .class_name = "BlackDetectContext",
+    .item_name  = blackdetect_get_name,
+    .option     = blackdetect_options,
+};
+
+#define YUVJ_FORMATS \
+    PIX_FMT_YUVJ420P, PIX_FMT_YUVJ422P, PIX_FMT_YUVJ444P, PIX_FMT_YUVJ440P
+
+static enum PixelFormat yuvj_formats[] = {
+    YUVJ_FORMATS, PIX_FMT_NONE
+};
+
+static int query_formats(AVFilterContext *ctx)
+{
+    static const enum PixelFormat pix_fmts[] = {
+        PIX_FMT_YUV410P, PIX_FMT_YUV420P, PIX_FMT_GRAY8, PIX_FMT_NV12,
+        PIX_FMT_NV21, PIX_FMT_YUV444P, PIX_FMT_YUV422P, PIX_FMT_YUV411P,
+        YUVJ_FORMATS,
+        PIX_FMT_NONE
+    };
+
+    avfilter_set_common_pixel_formats(ctx, avfilter_make_format_list(pix_fmts));
+    return 0;
+}
+
+static av_cold int init(AVFilterContext *ctx, const char *args, void *opaque)
+{
+    int ret;
+    BlackDetectContext *blackdetect = ctx->priv;
+
+    blackdetect->class = &blackdetect_class;
+    av_opt_set_defaults(blackdetect);
+
+    if ((ret = av_set_options_string(blackdetect, args, "=", ":")) < 0) {
+        av_log(ctx, AV_LOG_ERROR, "Error parsing options string: '%s'\n", args);
+        return ret;
+    }
+
+    return 0;
+}
+
+static int config_input(AVFilterLink *inlink)
+{
+    AVFilterContext *ctx = inlink->dst;
+    BlackDetectContext *blackdetect = ctx->priv;
+
+    blackdetect->black_min_duration =
+        blackdetect->black_min_duration_time / av_q2d(inlink->time_base);
+
+    blackdetect->pixel_black_th_i = ff_fmt_is_in(inlink->format, yuvj_formats) ?
+        // luminance_minimum_value + pixel_black_th * luminance_range_size
+             blackdetect->pixel_black_th *  255 :
+        16 + blackdetect->pixel_black_th * (235 - 16);
+
+    av_log(blackdetect, AV_LOG_INFO,
+           "black_min_duration:%s pixel_black_th:%f pixel_black_th_i:%d picture_black_ratio_th:%f\n",
+           av_ts2timestr(blackdetect->black_min_duration, &inlink->time_base),
+           blackdetect->pixel_black_th, blackdetect->pixel_black_th_i,
+           blackdetect->picture_black_ratio_th);
+    return 0;
+}
+
+static void draw_slice(AVFilterLink *inlink, int y, int h, int slice_dir)
+{
+    AVFilterContext *ctx = inlink->dst;
+    BlackDetectContext *blackdetect = ctx->priv;
+    AVFilterBufferRef *picref = inlink->cur_buf;
+    int x, i;
+    const uint8_t *p = picref->data[0] + y * picref->linesize[0];
+
+    for (i = 0; i < h; i++) {
+        for (x = 0; x < inlink->w; x++)
+            blackdetect->nb_black_pixels += p[x] <= blackdetect->pixel_black_th_i;
+        p += picref->linesize[0];
+    }
+
+    avfilter_draw_slice(ctx->outputs[0], y, h, slice_dir);
+}
+
+static void end_frame(AVFilterLink *inlink)
+{
+    AVFilterContext *ctx = inlink->dst;
+    BlackDetectContext *blackdetect = ctx->priv;
+    AVFilterBufferRef *picref = inlink->cur_buf;
+    double picture_black_ratio = 0;
+
+    picture_black_ratio = (double)blackdetect->nb_black_pixels / (inlink->w * inlink->h);
+
+    av_log(ctx, AV_LOG_DEBUG,
+           "frame:%u picture_black_ratio:%f pos:%"PRId64" pts:%s t:%s type:%c\n",
+           blackdetect->frame_count, picture_black_ratio,
+           picref->pos, av_ts2str(picref->pts),
+           av_ts2timestr(blackdetect->black_start, &inlink->time_base),
+           av_get_picture_type_char(picref->video->pict_type));
+
+    if (picture_black_ratio >= blackdetect->picture_black_ratio_th) {
+        if (!blackdetect->black_started) {
+            /* black starts here */
+            blackdetect->black_started = 1;
+            blackdetect->black_start = picref->pts;
+        }
+    } else if (blackdetect->black_started) {
+        /* black ends here */
+        blackdetect->black_started = 0;
+        blackdetect->black_end = picref->pts;
+
+        if ((blackdetect->black_end - blackdetect->black_start) >= blackdetect->black_min_duration) {
+            av_log(blackdetect, AV_LOG_INFO,
+                   "black_start:%s black_end:%s black_duration:%s\n",
+                   av_ts2timestr(blackdetect->black_start, &inlink->time_base),
+                   av_ts2timestr(blackdetect->black_end, &inlink->time_base),
+                   av_ts2timestr(blackdetect->black_end - blackdetect->black_start, &inlink->time_base));
+        }
+    }
+
+    blackdetect->frame_count++;
+    blackdetect->nb_black_pixels = 0;
+    avfilter_end_frame(inlink->dst->outputs[0]);
+}
+
+AVFilter avfilter_vf_blackdetect = {
+    .name          = "blackdetect",
+    .description   = NULL_IF_CONFIG_SMALL("Detect video intervals that are (almost) black."),
+    .priv_size     = sizeof(BlackDetectContext),
+    .init          = init,
+    .query_formats = query_formats,
+
+    .inputs = (const AVFilterPad[]) {
+        { .name             = "default",
+          .type             = AVMEDIA_TYPE_VIDEO,
+          .config_props     = config_input,
+          .draw_slice       = draw_slice,
+          .get_video_buffer = avfilter_null_get_video_buffer,
+          .start_frame      = avfilter_null_start_frame,
+          .end_frame        = end_frame, },
+        { .name = NULL }
+    },
+
+    .outputs = (const AVFilterPad[]) {
+        { .name             = "default",
+          .type             = AVMEDIA_TYPE_VIDEO },
+        { .name = NULL }
+    },
+};