lavfi: add field filter

The filter is a port of libmpcodecs/vf_field.c, since there is no common
code I relicensed it as LGPL, while keeping the original author
copyright.

Changelog

@@ -18,6 +18,7 @@ version <next>:
 - LVF demuxer
 - ffescape tool
 - metadata (info chunk) support in CAF muxer
+- field filter ported from libmpcodecs
 
 
 version 1.0:

doc/filters.texi

@@ -2128,6 +2128,31 @@ fade=in:5:20
 fade=in:0:25:alpha=1
 @end example
 
+@section field
+
+Extract a single field from an interlaced image using stride
+arithmetic to avoid wasting CPU time. The output frames are marked as
+non-interlaced.
+
+This filter accepts the following named options:
+@table @option
+@item type
+Specify whether to extract the top (if the value is @code{0} or
+@code{top}) or the bottom field (if the value is @code{1} or
+@code{bottom}).
+@end table
+
+If the option key is not specified, the first value sets the @var{type}
+option. For example:
+@example
+field=bottom
+@end example
+
+is equivalent to:
+@example
+field=type=bottom
+@end example
+
 @section fieldorder
 
 Transform the field order of the input video.

libavfilter/Makefile

@@ -98,6 +98,7 @@ OBJS-$(CONFIG_DRAWBOX_FILTER)                += vf_drawbox.o
 OBJS-$(CONFIG_DRAWTEXT_FILTER)               += vf_drawtext.o
 OBJS-$(CONFIG_EDGEDETECT_FILTER)             += vf_edgedetect.o
 OBJS-$(CONFIG_FADE_FILTER)                   += vf_fade.o
+OBJS-$(CONFIG_FIELD_FILTER)                  += vf_field.o
 OBJS-$(CONFIG_FIELDORDER_FILTER)             += vf_fieldorder.o
 OBJS-$(CONFIG_FIFO_FILTER)                   += fifo.o
 OBJS-$(CONFIG_FORMAT_FILTER)                 += vf_format.o

libavfilter/allfilters.c

@@ -90,6 +90,7 @@ void avfilter_register_all(void)
     REGISTER_FILTER (DRAWTEXT,    drawtext,    vf);
     REGISTER_FILTER (EDGEDETECT,  edgedetect,  vf);
     REGISTER_FILTER (FADE,        fade,        vf);
+    REGISTER_FILTER (FIELD,       field,       vf);
     REGISTER_FILTER (FIELDORDER,  fieldorder,  vf);
     REGISTER_FILTER (FIFO,        fifo,        vf);
     REGISTER_FILTER (FORMAT,      format,      vf);

libavfilter/version.h

@@ -29,8 +29,8 @@
 #include "libavutil/avutil.h"
 
 #define LIBAVFILTER_VERSION_MAJOR  3
-#define LIBAVFILTER_VERSION_MINOR  20
-#define LIBAVFILTER_VERSION_MICRO 113
+#define LIBAVFILTER_VERSION_MINOR  21
+#define LIBAVFILTER_VERSION_MICRO 100
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \
                                                LIBAVFILTER_VERSION_MINOR, \

libavfilter/vf_field.c

+/*
+ * Copyright (c) 2003 Rich Felker
+ * 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
+ * field filter, based on libmpcodecs/vf_field.c by Rich Felker
+ */
+
+#include "libavutil/opt.h"
+#include "libavutil/pixdesc.h"
+#include "avfilter.h"
+#include "internal.h"
+
+enum FieldType { FIELD_TYPE_TOP = 0, FIELD_TYPE_BOTTOM };
+
+typedef struct {
+    const AVClass *class;
+    enum FieldType type;
+    int nb_planes;              ///< number of planes of the current format
+} FieldContext;
+
+#define OFFSET(x) offsetof(FieldContext, x)
+#define FLAGS AV_OPT_FLAG_FILTERING_PARAM|AV_OPT_FLAG_VIDEO_PARAM
+
+static const AVOption field_options[] = {
+    {"type", "set field type (top or bottom)", OFFSET(type), AV_OPT_TYPE_INT, {.i64=FIELD_TYPE_TOP}, 0, 1, FLAGS, "field_type" },
+    {"top",    "select top field",    0, AV_OPT_TYPE_CONST, {.i64=FIELD_TYPE_TOP},    INT_MIN, INT_MAX, FLAGS, "field_type"},
+    {"bottom", "select bottom field", 0, AV_OPT_TYPE_CONST, {.i64=FIELD_TYPE_BOTTOM}, INT_MIN, INT_MAX, FLAGS, "field_type"},
+
+    {NULL}
+};
+
+AVFILTER_DEFINE_CLASS(field);
+
+static av_cold int init(AVFilterContext *ctx, const char *args)
+{
+    FieldContext *field = ctx->priv;
+    static const char *shorthand[] = { "type", NULL };
+
+    field->class = &field_class;
+    av_opt_set_defaults(field);
+
+    return av_opt_set_from_string(field, args, shorthand, "=", ":");
+}
+
+static int config_props_output(AVFilterLink *outlink)
+{
+    AVFilterContext *ctx = outlink->src;
+    FieldContext *field = ctx->priv;
+    AVFilterLink *inlink = ctx->inputs[0];
+    const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(inlink->format);
+    int i;
+
+    for (i = 0; i < desc->nb_components; i++)
+        field->nb_planes = FFMAX(field->nb_planes, desc->comp[i].plane);
+    field->nb_planes++;
+
+    outlink->w = inlink->w;
+    outlink->h = (inlink->h + (field->type == FIELD_TYPE_TOP)) / 2;
+
+    av_log(ctx, AV_LOG_VERBOSE, "w:%d h:%d type:%s -> w:%d h:%d\n",
+           inlink->w, inlink->h, field->type == FIELD_TYPE_BOTTOM ? "bottom" : "top",
+           outlink->w, outlink->h);
+    return 0;
+}
+
+static int start_frame(AVFilterLink *inlink, AVFilterBufferRef *inpicref)
+{
+    FieldContext *field = inlink->dst->priv;
+    AVFilterBufferRef *outpicref = avfilter_ref_buffer(inpicref, ~0);
+    AVFilterLink *outlink = inlink->dst->outputs[0];
+    int i;
+
+    if (!outpicref)
+        return AVERROR(ENOMEM);
+
+    outpicref->video->h = outlink->h;
+    outpicref->video->interlaced = 0;
+
+    for (i = 0; i < field->nb_planes; i++) {
+        if (field->type == FIELD_TYPE_BOTTOM)
+            outpicref->data[i] = inpicref->data[i] + inpicref->linesize[i];
+        outpicref->linesize[i] = 2 * inpicref->linesize[i];
+    }
+    return ff_start_frame(outlink, outpicref);
+}
+
+static int draw_slice(AVFilterLink *inlink, int y, int h, int slice_dir)
+{
+    FieldContext *field = inlink->dst->priv;
+    int y1 = (y + (field->type == FIELD_TYPE_TOP)) / 2;
+    int h1 = (h + (field->type == FIELD_TYPE_TOP)) / 2;
+    return ff_draw_slice(inlink->dst->outputs[0], y1, h1, slice_dir);
+}
+
+static const AVFilterPad field_inputs[] = {
+    {
+        .name             = "default",
+        .type             = AVMEDIA_TYPE_VIDEO,
+        .get_video_buffer = ff_null_get_video_buffer,
+        .start_frame      = start_frame,
+        .draw_slice       = draw_slice,
+        .end_frame        = ff_null_end_frame,
+    },
+    { NULL }
+};
+
+static const AVFilterPad field_outputs[] = {
+    {
+        .name          = "default",
+        .type          = AVMEDIA_TYPE_VIDEO,
+        .config_props  = config_props_output,
+    },
+    { NULL }
+};
+
+AVFilter avfilter_vf_field = {
+    .name          = "field",
+    .description   = NULL_IF_CONFIG_SMALL("Extract a field from the input video."),
+
+    .priv_size     = sizeof(FieldContext),
+    .init          = init,
+
+    .inputs        = field_inputs,
+    .outputs       = field_outputs,
+    .priv_class    = &field_class,
+};

tests/fate/avfilter.mak

@@ -11,6 +11,7 @@ FATE_LAVFI = fate-lavfi-alphaextract_rgb                                \
              fate-lavfi-drawbox                                         \
              fate-lavfi-edgedetect                                      \
              fate-lavfi-fade                                            \
+             fate-lavfi-field                                           \
              fate-lavfi-idet                                            \
              fate-lavfi-life                                            \
              fate-lavfi-null                                            \

tests/lavfi-regression.sh

@@ -111,6 +111,7 @@ do_lavfi_pixfmts(){
 do_lavfi_pixfmts "copy"    ""
 do_lavfi_pixfmts "crop"    "100:100:100:100"
 do_lavfi_pixfmts "hflip"   ""
+do_lavfi_pixfmts "field"   "field" "bottom"
 do_lavfi_pixfmts "null"    ""
 do_lavfi_pixfmts "pad"     "500:400:20:20"
 do_lavfi_pixfmts "pixdesctest" ""

tests/ref/lavfi/field

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