Re: [FFmpeg-devel] [PATCH] avfilter: add backgroundkey video filter

[Paul B Mahol <onemda@gmail.com>]

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On 10/30/22, Paul B Mahol <onemda@gmail.com> wrote:
> Patch attached.
>

Improved patch attached.

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From 6f9873ca81557fa77d7af957dd7694d5cc6e8019 Mon Sep 17 00:00:00 2001
From: Paul B Mahol <onemda@gmail.com>
Date: Fri, 28 Oct 2022 22:02:29 +0200
Subject: [PATCH] avfilter: add backgroundkey video filter

Signed-off-by: Paul B Mahol <onemda@gmail.com>
---
 doc/filters.texi               |  19 +++
 libavfilter/Makefile           |   1 +
 libavfilter/allfilters.c       |   1 +
 libavfilter/vf_backgroundkey.c | 251 +++++++++++++++++++++++++++++++++
 4 files changed, 272 insertions(+)
 create mode 100644 libavfilter/vf_backgroundkey.c

diff --git a/doc/filters.texi b/doc/filters.texi
index bcd19cf931..6e95c3a908 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -7987,6 +7987,25 @@ The command accepts the same syntax of the corresponding option.
 If the specified expression is not valid, it is kept at its current
 value.
 
+@section backgroundkey
+
+Turns a static background into transparency.
+
+The filter accepts the following option:
+
+@table @option
+@item threshold
+Threshold for scene change detection.
+@item similarity
+Similarity percentage with the background.
+@item blend
+Set the blend amount for pixels that are not similar.
+@end table
+
+@subsection Commands
+This filter supports same @ref{commands} as options except option @code{s}.
+The command accepts the same syntax of the corresponding option.
+
 @section bbox
 
 Compute the bounding box for the non-black pixels in the input frame
diff --git a/libavfilter/Makefile b/libavfilter/Makefile
index 195e616ccc..0e971d5c3e 100644
--- a/libavfilter/Makefile
+++ b/libavfilter/Makefile
@@ -192,6 +192,7 @@ OBJS-$(CONFIG_AVGBLUR_FILTER)                += vf_avgblur.o
 OBJS-$(CONFIG_AVGBLUR_OPENCL_FILTER)         += vf_avgblur_opencl.o opencl.o \
                                                 opencl/avgblur.o boxblur.o
 OBJS-$(CONFIG_AVGBLUR_VULKAN_FILTER)         += vf_avgblur_vulkan.o vulkan.o vulkan_filter.o
+OBJS-$(CONFIG_BACKGROUNDKEY_FILTER)          += vf_backgroundkey.o
 OBJS-$(CONFIG_BBOX_FILTER)                   += bbox.o vf_bbox.o
 OBJS-$(CONFIG_BENCH_FILTER)                  += f_bench.o
 OBJS-$(CONFIG_BILATERAL_FILTER)              += vf_bilateral.o
diff --git a/libavfilter/allfilters.c b/libavfilter/allfilters.c
index 97225a3679..1e0391f7a4 100644
--- a/libavfilter/allfilters.c
+++ b/libavfilter/allfilters.c
@@ -178,6 +178,7 @@ extern const AVFilter ff_vf_atadenoise;
 extern const AVFilter ff_vf_avgblur;
 extern const AVFilter ff_vf_avgblur_opencl;
 extern const AVFilter ff_vf_avgblur_vulkan;
+extern const AVFilter ff_vf_backgroundkey;
 extern const AVFilter ff_vf_bbox;
 extern const AVFilter ff_vf_bench;
 extern const AVFilter ff_vf_bilateral;
diff --git a/libavfilter/vf_backgroundkey.c b/libavfilter/vf_backgroundkey.c
new file mode 100644
index 0000000000..2c2da60b39
--- /dev/null
+++ b/libavfilter/vf_backgroundkey.c
@@ -0,0 +1,251 @@
+/*
+ * 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
+ */
+
+#include "libavutil/opt.h"
+#include "libavutil/imgutils.h"
+#include "libavutil/intreadwrite.h"
+#include "avfilter.h"
+#include "formats.h"
+#include "internal.h"
+#include "video.h"
+
+typedef struct BackgroundkeyContext {
+    const AVClass *class;
+
+    float threshold;
+    float similarity;
+    float blend;
+    int max;
+
+    int nb_threads;
+    int hsub_log2;
+    int vsub_log2;
+
+    int64_t max_sum;
+    int64_t *sums;
+
+    AVFrame *background;
+
+    int (*do_slice)(AVFilterContext *avctx, void *arg,
+                    int jobnr, int nb_jobs);
+} BackgroundkeyContext;
+
+static int do_backgroundkey_slice(AVFilterContext *avctx, void *arg, int jobnr, int nb_jobs)
+{
+    BackgroundkeyContext *s = avctx->priv;
+    AVFrame *frame = arg;
+    const int slice_start = (frame->height * jobnr) / nb_jobs;
+    const int slice_end = (frame->height * (jobnr + 1)) / nb_jobs;
+    const int min_diff = (255 + 255 + 255) * s->similarity;
+    const float blend = s->blend;
+    const int hsub = s->hsub_log2;
+    const int vsub = s->vsub_log2;
+    int64_t sum = 0;
+
+    for (int y = slice_start; y < slice_end; y++) {
+        const uint8_t *srcy = frame->data[0] + frame->linesize[0] * y;
+        const uint8_t *srcu = frame->data[1] + frame->linesize[1] * (y >> vsub);
+        const uint8_t *srcv = frame->data[2] + frame->linesize[2] * (y >> vsub);
+        const uint8_t *bsrcy = s->background->data[0] + s->background->linesize[0] * y;
+        const uint8_t *bsrcu = s->background->data[1] + s->background->linesize[1] * (y >> vsub);
+        const uint8_t *bsrcv = s->background->data[2] + s->background->linesize[2] * (y >> vsub);
+        uint8_t *dst = frame->data[3] + frame->linesize[3] * y;
+        for (int x = 0; x < frame->width; x++) {
+            const int xx = x >> hsub;
+            const int diff = FFABS(srcy[x]  - bsrcy[x])  +
+                             FFABS(srcu[xx] - bsrcu[xx]) +
+                             FFABS(srcv[xx] - bsrcv[xx]);
+            int A;
+
+            sum += diff;
+            if (blend > 0.f) {
+                A = 255 - av_clipf((min_diff - diff) / blend, 0.f, 255.f);
+            } else {
+                A = (diff > min_diff) ? 255 : 0;
+            }
+
+            dst[x] = A;
+        }
+    }
+
+    s->sums[jobnr] = sum;
+
+    return 0;
+}
+
+static int do_backgroundkey16_slice(AVFilterContext *avctx, void *arg, int jobnr, int nb_jobs)
+{
+    BackgroundkeyContext *s = avctx->priv;
+    AVFrame *frame = arg;
+    const int slice_start = (frame->height * jobnr) / nb_jobs;
+    const int slice_end = (frame->height * (jobnr + 1)) / nb_jobs;
+    const int hsub = s->hsub_log2;
+    const int vsub = s->vsub_log2;
+    const int max = s->max;
+    const int min_diff = s->similarity * (s->max + s->max + s->max);
+    const float blend = s->blend;
+    int64_t sum = 0;
+
+    for (int y = slice_start; y < slice_end; y++) {
+        const uint16_t *srcy = (const uint16_t *)(frame->data[0] + frame->linesize[0] *  y);
+        const uint16_t *srcu = (const uint16_t *)(frame->data[1] + frame->linesize[1] * (y >> vsub));
+        const uint16_t *srcv = (const uint16_t *)(frame->data[2] + frame->linesize[2] * (y >> vsub));
+        const uint16_t *bsrcy = (const uint16_t *)(s->background->data[0] + s->background->linesize[0] *  y);
+        const uint16_t *bsrcu = (const uint16_t *)(s->background->data[1] + s->background->linesize[1] * (y >> vsub));
+        const uint16_t *bsrcv = (const uint16_t *)(s->background->data[2] + s->background->linesize[2] * (y >> vsub));
+        uint16_t *dst = (uint16_t *)(frame->data[3] + frame->linesize[3] * y);
+        for (int x = 0; x < frame->width; x++) {
+            const int xx = x >> hsub;
+            const int diff = FFABS(srcy[x]  - bsrcy[x] ) +
+                             FFABS(srcu[xx] - bsrcu[xx]) +
+                             FFABS(srcv[xx] - bsrcv[xx]);
+            int A;
+
+            sum += diff;
+            if (blend > 0.f) {
+                A = max - av_clipf((min_diff - diff) / blend, 0.f, max);
+            } else {
+                A = (diff > min_diff) ? max : 0;
+            }
+
+            dst[x] = A;
+        }
+    }
+
+    s->sums[jobnr] = sum;
+
+    return 0;
+}
+
+static int filter_frame(AVFilterLink *link, AVFrame *frame)
+{
+    AVFilterContext *avctx = link->dst;
+    BackgroundkeyContext *s = avctx->priv;
+    int64_t sum = 0;
+    int ret;
+
+    if (!s->background) {
+        s->background = av_frame_clone(frame);
+        if (!s->background)
+            return AVERROR(ENOMEM);
+        av_frame_make_writable(s->background);
+    }
+
+    if (ret = ff_filter_execute(avctx, s->do_slice, frame, NULL,
+                                FFMIN(frame->height, s->nb_threads)))
+        return ret;
+
+    for (int n = 0; n < s->nb_threads; n++)
+        sum += s->sums[n];
+    if (s->max_sum * s->threshold < sum) {
+        av_frame_free(&s->background);
+        s->background = av_frame_clone(frame);
+        if (!s->background)
+            return AVERROR(ENOMEM);
+        av_frame_make_writable(s->background);
+    }
+
+    return ff_filter_frame(avctx->outputs[0], frame);
+}
+
+static av_cold int config_output(AVFilterLink *outlink)
+{
+    const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(outlink->format);
+    AVFilterContext *avctx = outlink->src;
+    AVFilterLink *inlink = avctx->inputs[0];
+    BackgroundkeyContext *s = avctx->priv;
+    int depth;
+
+    s->nb_threads = ff_filter_get_nb_threads(avctx);
+    depth = desc->comp[0].depth;
+    s->do_slice = depth <= 8 ? do_backgroundkey_slice : do_backgroundkey16_slice;
+    s->max = (1 << depth) - 1;
+    s->hsub_log2 = desc->log2_chroma_w;
+    s->vsub_log2 = desc->log2_chroma_h;
+    s->max_sum  = (int64_t)(inlink->w) * inlink->h * s->max;
+    s->max_sum += 2LL * (inlink->w >> s->hsub_log2) * (inlink->h >> s->vsub_log2) * s->max;
+
+    s->sums = av_calloc(s->nb_threads, sizeof(*s->sums));
+    if (!s->sums)
+        return AVERROR(ENOMEM);
+
+    return 0;
+}
+
+static av_cold void uninit(AVFilterContext *ctx)
+{
+    BackgroundkeyContext *s = ctx->priv;
+
+    av_frame_free(&s->background);
+    av_freep(&s->sums);
+}
+
+static const AVFilterPad backgroundkey_inputs[] = {
+    {
+        .name         = "default",
+        .type         = AVMEDIA_TYPE_VIDEO,
+        .flags        = AVFILTERPAD_FLAG_NEEDS_WRITABLE,
+        .filter_frame = filter_frame,
+    },
+};
+
+static const AVFilterPad backgroundkey_outputs[] = {
+    {
+        .name         = "default",
+        .type         = AVMEDIA_TYPE_VIDEO,
+        .config_props = config_output,
+    },
+};
+
+#define OFFSET(x) offsetof(BackgroundkeyContext, x)
+#define FLAGS AV_OPT_FLAG_FILTERING_PARAM|AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_RUNTIME_PARAM
+
+static const AVOption backgroundkey_options[] = {
+    { "threshold",  "set the scene change threshold", OFFSET(threshold),  AV_OPT_TYPE_FLOAT, { .dbl = 0.05}, 0.0, 1.0, FLAGS },
+    { "similarity", "set the similarity",             OFFSET(similarity), AV_OPT_TYPE_FLOAT, { .dbl = 0.1 }, 0.0, 1.0, FLAGS },
+    { "blend",      "set the blend value",            OFFSET(blend),      AV_OPT_TYPE_FLOAT, { .dbl = 0.0 }, 0.0, 1.0, FLAGS },
+    { NULL }
+};
+
+static const enum AVPixelFormat backgroundkey_fmts[] = {
+    AV_PIX_FMT_YUVA420P,
+    AV_PIX_FMT_YUVA422P,
+    AV_PIX_FMT_YUVA444P,
+    AV_PIX_FMT_YUVA420P9,  AV_PIX_FMT_YUVA422P9,  AV_PIX_FMT_YUVA444P9,
+    AV_PIX_FMT_YUVA420P10, AV_PIX_FMT_YUVA422P10, AV_PIX_FMT_YUVA444P10,
+    AV_PIX_FMT_YUVA422P12, AV_PIX_FMT_YUVA444P12,
+    AV_PIX_FMT_YUVA420P16, AV_PIX_FMT_YUVA422P16, AV_PIX_FMT_YUVA444P16,
+    AV_PIX_FMT_GBRAP,
+    AV_PIX_FMT_GBRAP10, AV_PIX_FMT_GBRAP12, AV_PIX_FMT_GBRAP16,
+    AV_PIX_FMT_NONE
+};
+
+AVFILTER_DEFINE_CLASS(backgroundkey);
+
+const AVFilter ff_vf_backgroundkey = {
+    .name            = "backgroundkey",
+    .description     = NULL_IF_CONFIG_SMALL("Turns a static background into transparency."),
+    .priv_size       = sizeof(BackgroundkeyContext),
+    .priv_class      = &backgroundkey_class,
+    .uninit          = uninit,
+    FILTER_INPUTS(backgroundkey_inputs),
+    FILTER_OUTPUTS(backgroundkey_outputs),
+    FILTER_PIXFMTS_ARRAY(backgroundkey_fmts),
+    .flags           = AVFILTER_FLAG_SUPPORT_TIMELINE_GENERIC | AVFILTER_FLAG_SLICE_THREADS,
+    .process_command = ff_filter_process_command,
+};
-- 
2.37.2


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