vo: dropping subtitle files on the VO window adds them as subtitle files

Note that we don't try to be clever about detecting the files as
subtitles: we just check the file extension. We could go all the way and
check the files by opening them with a demuxer, but that would probably
do more bad than good.

sub/find_subfiles.c

@@ -42,6 +42,11 @@ static struct bstr get_ext(struct bstr s)
     return bstr_splice(s, dotpos + 1, s.len);
 }
 
+bool mp_might_be_subtitle_file(const char *filename)
+{
+    return is_sub_ext(get_ext(bstr0(filename)));
+}
+
 static int compare_sub_filename(const void *a, const void *b)
 {
     const struct subfn *s1 = a;

sub/find_subfiles.h

@@ -19,6 +19,8 @@
 #ifndef MPLAYER_FIND_SUBFILES_H
 #define MPLAYER_FIND_SUBFILES_H
 
+#include <stdbool.h>
+
 struct subfn {
     int priority;
     char *fname;
@@ -28,4 +30,6 @@ struct subfn {
 struct mpv_global;
 struct subfn *find_text_subtitles(struct mpv_global *global, const char *fname);
 
+bool mp_might_be_subtitle_file(const char *filename);
+
 #endif /* MPLAYER_FINDFILES_H */

video/out/vo.c

@@ -43,6 +43,7 @@
 #include "video/mp_image.h"
 #include "video/vfcap.h"
 #include "sub/osd.h"
+#include "sub/find_subfiles.h"
 
 //
 // Externally visible list of all vo drivers
@@ -631,6 +632,20 @@ static void run_cmd(struct vo *vo, const char **cmd)
 // Handle drag & drop event of a list of files on the VO window.
 void vo_drop_files(struct vo *vo, int num_files, char **files)
 {
+    bool all_sub = true;
+    for (int i = 0; i < num_files; i++)
+        all_sub &= mp_might_be_subtitle_file(files[i]);
+
+    if (all_sub) {
+        for (int i = 0; i < num_files; i++) {
+            const char *cmd[] = {
+                "sub_add",
+                files[i],
+                NULL
+            };
+            run_cmd(vo, cmd);
+        }
+    } else {
         for (int i = 0; i < num_files; i++) {
             const char *cmd[] = {
                 "loadfile",
@@ -644,3 +659,4 @@ void vo_drop_files(struct vo *vo, int num_files, char **files)
             run_cmd(vo, cmd);
         }
     }
+}