[FFmpeg-devel] suggested patch: avfilter/vf_subtitles: add support for subtitles font scaling

[Sergey]

Hello.

Recently I used ffmpeg to embed subtitles, and I needed to scale them.

I thought "original_size" option scales subtitles, but it does not.
So I wrote a short patch for it to do that (attached)

If that is considered too complex/bad idea I've also attached another patch
that adds a "font_scale" option instead.

I hope you like one of these.
-- 
diff -ur ffmpeg-HEAD-649b7a9/libavfilter/vf_subtitles.c ffmpeg-HEAD-649b7a9.new/libavfilter/vf_subtitles.c
--- ffmpeg-HEAD-649b7a9/libavfilter/vf_subtitles.c	2014-09-10 00:07:59.000000000 +0000
+++ ffmpeg-HEAD-649b7a9.new/libavfilter/vf_subtitles.c	2014-09-10 00:11:26.000000000 +0000
@@ -136,9 +136,11 @@
     ff_draw_init(&ass->draw, inlink->format, 0);
 
     ass_set_frame_size  (ass->renderer, inlink->w, inlink->h);
-    if (ass->original_w && ass->original_h)
+    if (ass->original_w && ass->original_h) {
         ass_set_aspect_ratio(ass->renderer, (double)inlink->w / inlink->h,
                              (double)ass->original_w / ass->original_h);
+        ass_set_font_scale(ass->renderer, (inlink->w + inlink->h) * 1.0 / (ass->original_w + ass->original_h));
+    }
 
     return 0;
 }

diff -ur ffmpeg-HEAD-649b7a9/libavfilter/vf_subtitles.c ffmpeg-HEAD-649b7a9.new/libavfilter/vf_subtitles.c
--- ffmpeg-HEAD-649b7a9/libavfilter/vf_subtitles.c	2014-09-10 01:02:49.000000000 +0000
+++ ffmpeg-HEAD-649b7a9.new/libavfilter/vf_subtitles.c	2014-09-10 03:34:19.000000000 +0000
@@ -55,6 +55,7 @@
     uint8_t rgba_map[4];
     int     pix_step[4];       ///< steps per pixel for each plane of the main output
     int original_w, original_h;
+    double font_scale;
     FFDrawContext draw;
 } AssContext;
 
@@ -65,6 +66,7 @@
     {"filename",       "set the filename of file to read",                         OFFSET(filename),   AV_OPT_TYPE_STRING,     {.str = NULL},  CHAR_MIN, CHAR_MAX, FLAGS }, \
     {"f",              "set the filename of file to read",                         OFFSET(filename),   AV_OPT_TYPE_STRING,     {.str = NULL},  CHAR_MIN, CHAR_MAX, FLAGS }, \
     {"original_size",  "set the size of the original video (used to scale fonts)", OFFSET(original_w), AV_OPT_TYPE_IMAGE_SIZE, {.str = NULL},  CHAR_MIN, CHAR_MAX, FLAGS }, \
+    {"font_scale",     "set font scale",                                           OFFSET(font_scale), AV_OPT_TYPE_DOUBLE,     {.dbl = 1},     0.01,     99,       FLAGS }, \
 
 /* libass supports a log level ranging from 0 to 7 */
 static const int ass_libavfilter_log_level_map[] = {
@@ -139,6 +141,7 @@
     if (ass->original_w && ass->original_h)
         ass_set_aspect_ratio(ass->renderer, (double)inlink->w / inlink->h,
                              (double)ass->original_w / ass->original_h);
+    ass_set_font_scale(ass->renderer, ass->font_scale);
 
     return 0;
 }

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