osd: customizable subtitle and OSD position

You can set in which "corner" the OSD and subtitles are shown. I'd
prefer it a bit more general (so you could set the alignment using
a factor), but the libass API does not provide this.

DOCS/man/options.rst

@@ -2540,6 +2540,17 @@ OSD
 
     Default: 22.
 
+``--osd-align-x=<left|center|right>``,  ``--sub-text-align-x=...``
+    Control to which corner of the screen OSD or text subtitles should be
+    aligned to (default: ``center`` for subs, ``left`` for OSD).
+
+    Never applied to ASS subtitles, except in ``--no-sub-ass`` mode. Likewise,
+    this does not apply to image subtitles.
+
+``--osd-align-y=<top|center|bottom>`` ``--sub-text-align-y=...``
+    Vertical position (default: ``bottom`` for subs, ``top`` for OSD).
+    Details see ``--osd-align-x``.
+
 ``--osd-scale=<factor>``
     OSD font size multiplier, multiplied with ``--osd-font-size`` value.
 

sub/ass_mp.c

@@ -83,6 +83,7 @@ void mp_ass_set_style(ASS_Style *style, double res_y,
     style->MarginV = opts->margin_y * scale;
     style->ScaleX = 1.;
     style->ScaleY = 1.;
+    style->Alignment = 1 + (opts->align_x + 1) + (opts->align_y + 2) % 3 * 4;
 #if LIBASS_VERSION >= 0x01020000
     style->Blur = opts->blur;
 #endif

sub/osd.c

@@ -54,6 +54,10 @@ static const m_option_t style_opts[] = {
     OPT_FLOATRANGE("spacing", spacing, 0, -10, 10),
     OPT_INTRANGE("margin-x", margin_x, 0, 0, 300),
     OPT_INTRANGE("margin-y", margin_y, 0, 0, 600),
+    OPT_CHOICE("align-x", align_x, 0,
+               ({"left", -1}, {"center", 0}, {"right", +1})),
+    OPT_CHOICE("align-y", align_y, 0,
+               ({"top", -1}, {"center", 0}, {"bottom", +1})),
     OPT_FLOATRANGE("blur", blur, 0, 0, 20),
     {0}
 };
@@ -71,6 +75,8 @@ const struct m_sub_options osd_style_conf = {
         .shadow_offset = 0,
         .margin_x = 25,
         .margin_y = 22,
+        .align_x = -1,
+        .align_y = -1,
     },
 };
 
@@ -87,6 +93,8 @@ const struct m_sub_options sub_style_conf = {
         .shadow_offset = 0,
         .margin_x = 25,
         .margin_y = 22,
+        .align_x = 0,
+        .align_y = 1,
     },
 };
 

sub/osd.h

@@ -133,6 +133,8 @@ struct osd_style_opts {
     float spacing;
     int margin_x;
     int margin_y;
+    int align_x;
+    int align_y;
     float blur;
 };