avcodec/ttmlenc: add support for region positioning and sizing

The ASS margins are utilized to generate percentual values, as
the usage of cell-based sizing and offsetting seems to be not too
well supported by renderers.

Signed-off-by: Jan Ekström <jan.ekstrom@24i.com>

1 files changed, 43 insertions, 2 deletions

diff --git a/libavcodec/ttmlenc.c b/libavcodec/ttmlenc.c
index 37372b29cd..6dfcc0a216 100644
--- a/libavcodec/ttmlenc.c
+++ b/libavcodec/ttmlenc.c
@@ -237,11 +237,35 @@ static const char *ttml_get_text_alignment(int alignment)
     }
 }
 
+static void ttml_get_origin(ASSScriptInfo script_info, ASSStyle style,
+                           int *origin_left, int *origin_top)
+{
+    *origin_left = av_rescale(style.margin_l, 100, script_info.play_res_x);
+    *origin_top  =
+        av_rescale((style.alignment >= 7) ? style.margin_v : 0,
+                   100, script_info.play_res_y);
+}
+
+static void ttml_get_extent(ASSScriptInfo script_info, ASSStyle style,
+                           int *width, int *height)
+{
+    *width  = av_rescale(script_info.play_res_x - style.margin_r,
+                         100, script_info.play_res_x);
+    *height = av_rescale((style.alignment <= 3) ?
+                         script_info.play_res_y - style.margin_v :
+                         script_info.play_res_y,
+                         100, script_info.play_res_y);
+}
+
 static int ttml_write_region(AVCodecContext *avctx, AVBPrint *buf,
-                             ASSStyle style)
+                             ASSScriptInfo script_info, ASSStyle style)
 {
     const char *display_alignment = NULL;
     const char *text_alignment = NULL;
+    int origin_left = 0;
+    int origin_top  = 0;
+    int width = 0;
+    int height = 0;
 
     if (!style.name) {
         av_log(avctx, AV_LOG_ERROR, "Subtitle style name not set!\n");
@@ -254,6 +278,14 @@ static int ttml_write_region(AVCodecContext *avctx, AVBPrint *buf,
         return AVERROR_INVALIDDATA;
     }
 
+    if (style.margin_l < 0 || style.margin_r < 0 || style.margin_v < 0) {
+        av_log(avctx, AV_LOG_ERROR,
+               "One or more negative margin values in subtitle style: "
+               "left: %d, right: %d, vertical: %d!\n",
+               style.margin_l, style.margin_r, style.margin_v);
+        return AVERROR_INVALIDDATA;
+    }
+
     display_alignment = ttml_get_display_alignment(style.alignment);
     text_alignment = ttml_get_text_alignment(style.alignment);
     if (!display_alignment || !text_alignment) {
@@ -265,11 +297,19 @@ static int ttml_write_region(AVCodecContext *avctx, AVBPrint *buf,
         return AVERROR_INVALIDDATA;
     }
 
+    ttml_get_origin(script_info, style, &origin_left, &origin_top);
+    ttml_get_extent(script_info, style, &width, &height);
+
     av_bprintf(buf, "      <region xml:id=\"");
     av_bprint_escape(buf, style.name, NULL, AV_ESCAPE_MODE_XML,
                      AV_ESCAPE_FLAG_XML_DOUBLE_QUOTES);
     av_bprintf(buf, "\"\n");
 
+    av_bprintf(buf, "        tts:origin=\"%d%% %d%%\"\n",
+               origin_left, origin_top);
+    av_bprintf(buf, "        tts:extent=\"%d%% %d%%\"\n",
+               width, height);
+
     av_bprintf(buf, "        tts:displayAlign=\"");
     av_bprint_escape(buf, display_alignment, NULL, AV_ESCAPE_MODE_XML,
                      AV_ESCAPE_FLAG_XML_DOUBLE_QUOTES);
@@ -331,7 +371,8 @@ static int ttml_write_header_content(AVCodecContext *avctx)
     av_bprintf(&s->buffer, "    <layout>\n");
 
     for (int i = 0; i < ass->styles_count; i++) {
-        int ret = ttml_write_region(avctx, &s->buffer, ass->styles[i]);
+        int ret = ttml_write_region(avctx, &s->buffer, script_info,
+                                    ass->styles[i]);
         if (ret < 0)
             return ret;
     }