libvlc: add SPU scale getter

This fixes the compilation broken in 632c0c78 that used non-existing API

libvlc/patches/0018-lib-add-libvlc_video_get_spu_text_scale-API.patch

+From a85164a9d9322211ccd9b273dda0866740357e83 Mon Sep 17 00:00:00 2001
+From: =?UTF-8?q?Felix=20Paul=20K=C3=BChne?= <felix@feepk.net>
+Date: Tue, 27 Oct 2020 10:27:06 +0100
+Subject: [PATCH 18/18] lib: add libvlc_video_get_spu_text_scale API
+
+This complements 67c4ffd5.
+---
+ include/vlc/libvlc_media_player.h | 11 +++++++++++
+ lib/libvlc.sym                    |  1 +
+ lib/video.c                       | 12 ++++++++++++
+ 3 files changed, 24 insertions(+)
+
+diff --git a/include/vlc/libvlc_media_player.h b/include/vlc/libvlc_media_player.h
+index fea7034644..a017d6c1cf 100644
+--- a/include/vlc/libvlc_media_player.h
++++ b/include/vlc/libvlc_media_player.h
+@@ -1648,6 +1648,17 @@ LIBVLC_API int libvlc_video_update_viewpoint( libvlc_media_player_t *p_mi,
+  */
+ LIBVLC_API int64_t libvlc_video_get_spu_delay( libvlc_media_player_t *p_mi );
+ 
++/**
++ * Get the current subtitle text scale
++ *
++ * The scale factor is expressed as a percentage of the default size, where
++ * 1.0 represents 100 percent.
++ *
++ * \param p_mi media player
++ * \version LibVLC 4.0.0 or later
++ */
++LIBVLC_API float libvlc_video_get_spu_text_scale( libvlc_media_player_t *p_mi );
++
+ /**
+  * Set the subtitle text scale.
+  *
+diff --git a/lib/libvlc.sym b/lib/libvlc.sym
+index 2bb67eccf8..5d9713cdb3 100644
+--- a/lib/libvlc.sym
++++ b/lib/libvlc.sym
+@@ -239,6 +239,7 @@ libvlc_video_get_spu
+ libvlc_video_get_spu_count
+ libvlc_video_get_spu_delay
+ libvlc_video_get_spu_description
++libvlc_video_get_spu_text_scale
+ libvlc_video_get_teletext
+ libvlc_video_get_track
+ libvlc_video_get_track_count
+diff --git a/lib/video.c b/lib/video.c
+index e06adf143b..d3cba035d8 100644
+--- a/lib/video.c
++++ b/lib/video.c
+@@ -368,6 +368,18 @@ int libvlc_video_set_spu_delay( libvlc_media_player_t *p_mi,
+     return 0;
+ }
+ 
++float libvlc_video_get_spu_text_scale( libvlc_media_player_t *p_mi )
++{
++    vlc_player_t *player = p_mi->player;
++    vlc_player_Lock(player);
++
++    unsigned scale = vlc_player_GetSubtitleTextScale(player);
++
++    vlc_player_Unlock(player);
++
++    return scale / 100.f;
++}
++
+ void libvlc_video_set_spu_text_scale( libvlc_media_player_t *p_mi,
+                                       float f_scale )
+ {
+-- 
+2.24.3 (Apple Git-128)
+