1 files changed, 117 insertions, 0 deletions
diff --git a/libavfilter/vf_alphaextract.c b/libavfilter/vf_alphaextract.c
new file mode 100644
index 0000000000..102af9d38a
--- /dev/null
+++ b/libavfilter/vf_alphaextract.c
@@ -0,0 +1,117 @@
+/*
+ * Copyright (c) 2012 Steven Robertson
+ *
+ * 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
+ * simple channel-swapping filter to get at the alpha component
+ */
+
+#include <string.h>
+
+#include "libavutil/pixfmt.h"
+#include "avfilter.h"
+#include "drawutils.h"
+#include "formats.h"
+#include "video.h"
+
+enum { Y, U, V, A };
+
+typedef struct {
+    int is_packed_rgb;
+    uint8_t rgba_map[4];
+} AlphaExtractContext;
+
+static int query_formats(AVFilterContext *ctx)
+{
+    enum AVPixelFormat in_fmts[] = {
+        AV_PIX_FMT_YUVA444P, AV_PIX_FMT_YUVA422P, AV_PIX_FMT_YUVA420P,
+        AV_PIX_FMT_RGBA, AV_PIX_FMT_BGRA, AV_PIX_FMT_ARGB, AV_PIX_FMT_ABGR,
+        AV_PIX_FMT_NONE
+    };
+    enum AVPixelFormat out_fmts[] = { AV_PIX_FMT_GRAY8, AV_PIX_FMT_NONE };
+    ff_formats_ref(ff_make_format_list(in_fmts), &ctx->inputs[0]->out_formats);
+    ff_formats_ref(ff_make_format_list(out_fmts), &ctx->outputs[0]->in_formats);
+    return 0;
+}
+
+static int config_input(AVFilterLink *inlink)
+{
+    AlphaExtractContext *extract = inlink->dst->priv;
+    extract->is_packed_rgb =
+        ff_fill_rgba_map(extract->rgba_map, inlink->format) >= 0;
+    return 0;
+}
+
+static int draw_slice(AVFilterLink *inlink, int y0, int h, int slice_dir)
+{
+    AlphaExtractContext *extract = inlink->dst->priv;
+    AVFilterBufferRef *cur_buf = inlink->cur_buf;
+    AVFilterBufferRef *out_buf = inlink->dst->outputs[0]->out_buf;
+
+    if (extract->is_packed_rgb) {
+        int x, y;
+        uint8_t *pin, *pout;
+        for (y = y0; y < (y0 + h); y++) {
+            pin = cur_buf->data[0] + y * cur_buf->linesize[0] + extract->rgba_map[A];
+            pout = out_buf->data[0] + y * out_buf->linesize[0];
+            for (x = 0; x < out_buf->video->w; x++) {
+                *pout = *pin;
+                pout += 1;
+                pin += 4;
+            }
+        }
+    } else if (cur_buf->linesize[A] == out_buf->linesize[Y]) {
+        const int linesize = cur_buf->linesize[A];
+        memcpy(out_buf->data[Y] + y0 * linesize,
+               cur_buf->data[A] + y0 * linesize,
+               linesize * h);
+    } else {
+        const int linesize = FFMIN(out_buf->linesize[Y], cur_buf->linesize[A]);
+        int y;
+        for (y = y0; y < (y0 + h); y++) {
+            memcpy(out_buf->data[Y] + y * out_buf->linesize[Y],
+                   cur_buf->data[A] + y * cur_buf->linesize[A],
+                   linesize);
+        }
+    }
+    return ff_draw_slice(inlink->dst->outputs[0], y0, h, slice_dir);
+}
+
+AVFilter avfilter_vf_alphaextract = {
+    .name           = "alphaextract",
+    .description    = NULL_IF_CONFIG_SMALL("Extract an alpha channel as a "
+                      "grayscale image component."),
+    .priv_size      = sizeof(AlphaExtractContext),
+    .query_formats  = query_formats,
+
+    .inputs    = (const AVFilterPad[]) {
+        { .name             = "default",
+          .type             = AVMEDIA_TYPE_VIDEO,
+          .config_props     = config_input,
+          .draw_slice       = draw_slice,
+          .min_perms        = AV_PERM_READ },
+        { .name = NULL }
+    },
+    .outputs   = (const AVFilterPad[]) {
+      { .name               = "default",
+        .type               = AVMEDIA_TYPE_VIDEO, },
+      { .name = NULL }
+    },
+};