examples: add scaling_video example

This example should be useful to show the basic functionality of the
libswscale API.

More advanced features (scaling options etc., colorspace tweaking) may be
added later.

doc/examples/Makefile

@@ -16,6 +16,7 @@ EXAMPLES=       decoding_encoding                  \
                 filtering_audio                    \
                 metadata                           \
                 muxing                             \
+                scaling_video                      \
 
 OBJS=$(addsuffix .o,$(EXAMPLES))
 
@@ -28,7 +29,7 @@ muxing:            LDLIBS += -lm
 all: $(OBJS) $(EXAMPLES)
 
 clean-test:
-	$(RM) -f test*.pgm test.h264 test.mp2 test.sw test.mpg
+	$(RM) -f test*.pgm test.h264 test.mp2 test.sw test.mpg outscale*.pgm
 
 clean: clean-test
 	$(RM) -f $(EXAMPLES) $(OBJS)

doc/examples/scaling_video.c

@@ -0,0 +1,131 @@
+/*
+ * Copyright (c) 2012 Stefano Sabatini
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <libavutil/imgutils.h>
+#include <libavutil/parseutils.h>
+#include <libswscale/swscale.h>
+
+static void fill_yuv_image(uint8_t *data[4], int linesize[4],
+                           int width, int height, int frame_index)
+{
+    int x, y, i;
+
+    i = frame_index;
+
+    /* Y */
+    for (y = 0; y < height; y++)
+        for (x = 0; x < width; x++)
+            data[0][y * linesize[0] + x] = x + y + i * 3;
+
+    /* Cb and Cr */
+    for (y = 0; y < height / 2; y++) {
+        for (x = 0; x < width / 2; x++) {
+            data[1][y * linesize[1] + x] = 128 + y + i * 2;
+            data[2][y * linesize[2] + x] = 64 + x + i * 5;
+        }
+    }
+}
+
+static void save_pgm(const char *filename,
+                     const uint8_t *data, int linesize, int width, int height)
+{
+    FILE *f;
+    int i;
+
+    f = fopen(filename, "w");
+    fprintf(f, "P5\n%d %d\n%d\n", width, height, 255);
+    for (i = 0; i < height; i++)
+        fwrite(data + i * linesize, 1, width, f);
+    fclose(f);
+}
+
+int main(int argc, char **argv)
+{
+    uint8_t *src_data[4], *dst_data[4];
+    int src_linesize[4], dst_linesize[4];
+    int src_w = 320, src_h = 240, dst_w, dst_h;
+    enum PixelFormat src_pix_fmt = PIX_FMT_YUV420P, dst_pix_fmt = PIX_FMT_GRAY8;
+    const char *dst_size = argv[1];
+    struct SwsContext *sws_ctx;
+    int i, ret;
+
+    if (argc != 2) {
+        fprintf(stderr, "Usage: %s output_size\n"
+                "API example program to show how to scale an image with libswscale.\n"
+                "This program generates a series of pictures, rescales them to the given "
+                "<output size> and finally saves the rescaled pictures as PGM files named "
+                "like outscale<frame number>.pgm.\n"
+                "\n", argv[0]);
+        exit(1);
+    }
+
+    if (av_parse_video_size(&dst_w, &dst_h, dst_size) < 0) {
+        av_log(NULL, AV_LOG_ERROR,
+               "Invalid size '%s', must be in the form WxH or a valid size abbreviation\n",
+               dst_size);
+        exit(1);
+    }
+
+    /* create scaling context */
+    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(NULL, 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;
+    }
+
+    /* allocate source and destination image buffers */
+    if ((ret = av_image_alloc(src_data, src_linesize,
+                              src_w, src_h, src_pix_fmt, 16)) < 0)
+        goto end;
+
+    if ((ret = av_image_alloc(dst_data, dst_linesize,
+                              dst_w, dst_h, dst_pix_fmt, 16)) < 0)
+        goto end;
+
+    for (i = 0; i < 100; i++) {
+        char filename[1024];
+
+        /* generate synthetic video */
+        fill_yuv_image(src_data, src_linesize, src_w, src_h, i);
+
+        /* convert to destination format */
+        sws_scale(sws_ctx, (const uint8_t * const*)src_data,
+                  src_linesize, 0, src_h, dst_data, dst_linesize);
+
+        /* write Y plane to to output PGM file */
+        snprintf(filename, sizeof(filename), "outscale%02d.pgm", i);
+        save_pgm(filename, dst_data[0], dst_linesize[0], dst_w, dst_h);
+    }
+
+end:
+    av_freep(&src_data[0]);
+    av_freep(&dst_data[0]);
+    sws_freeContext(sws_ctx);
+    return ret < 0;
+}