lavfi: port libmpcodecs remove-logo filter

The code is based on the remove-logo filter in MPlayer/libmpcodecs, by
Robert Edele, relicensed to LGPL with consent of the author.

Address trac issue #249.

libavfilter/lswsutils.c

@@ -0,0 +1,50 @@
+/*
+ * 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/imgutils.h"
+#include "lswsutils.h"
+
+int ff_scale_image(uint8_t *dst_data[4], int dst_linesize[4],
+                   int dst_w, int dst_h, enum PixelFormat dst_pix_fmt,
+                   uint8_t * const src_data[4], int src_linesize[4],
+                   int src_w, int src_h, enum PixelFormat src_pix_fmt,
+                   void *log_ctx)
+{
+    int ret;
+    struct SwsContext *sws_ctx = sws_getContext(src_w, src_h, src_pix_fmt,
+                                                dst_w, dst_h, dst_pix_fmt,
+                                                SWS_BILINEAR, NULL, NULL, NULL);
+    if (!sws_ctx) {
+        av_log(log_ctx, AV_LOG_ERROR,
+               "Impossible to create scale context for the conversion "
+               "fmt:%s s:%dx%d -> fmt:%s s:%dx%d\n",
+               av_get_pix_fmt_name(src_pix_fmt), src_w, src_h,
+               av_get_pix_fmt_name(dst_pix_fmt), dst_w, dst_h);
+        ret = AVERROR(EINVAL);
+        goto end;
+    }
+
+    if ((ret = av_image_alloc(dst_data, dst_linesize, dst_w, dst_h, dst_pix_fmt, 16)) < 0)
+        goto end;
+    ret = 0;
+    sws_scale(sws_ctx, src_data, src_linesize, 0, src_h, dst_data, dst_linesize);
+
+end:
+    sws_freeContext(sws_ctx);
+    return ret;
+}