stats: make the OSD usable in audio-only mode

Previously, the script would throw garbage (ASS tags) at the terminal
when the bound key was pressed. This changes the behaviour to _not_
print any ASS tags (and replace those which can be interpreted by the
terminal) if there's no video.

I cleaned the patch up since you mentioned you were busy. As I said
before, there is absolutely no problem with calling mpv to display
strings to the OSD without any video. They'll just go straight to the
terminal just as they would with an active VO.

player/lua/stats.lua

@@ -13,6 +13,7 @@
 require 'mp.options'
 
 local o = {
+    no_osd = 0,
     duration = 3,
     -- text formatting
     font = "Source Sans Pro",
@@ -29,6 +30,13 @@ local o = {
     prop_indent = "\\h\\h\\h\\h\\h",
     kv_sep = "\\h\\h",  -- key<kv_sep>value
 
+    b1 = "{\\b1}",
+    b0 = "{\\b0}",
+    i1 = "{\\i1}",
+    i0 = "{\\i0}",
+    u1 = "{\\u1}",
+    u0 = "{\\u0}",
+
     -- Custom header for ASS tags to format the text output.
     -- Specifying this will ignore the text formatting values above and just
     -- use this string instead.
@@ -45,6 +53,20 @@ function main()
         audio = ""
     }
 
+    if mp.get_property("video-codec") == nil then
+        o.nl = "\n"
+        duration = mp.get_property("length")
+        o.prop_indent = "\t"
+        o.kv_sep = ""
+        o.b1 = ""
+        o.b0 = ""
+        o.i1 = ""
+        o.i0 = ""
+        o.u1 = ""
+        o.u0 = ""
+        o.no_osd = 1
+    end
+
     add_header(stats)
     add_file(stats)
     add_video(stats)
@@ -117,6 +139,9 @@ end
 
 
 function add_header(s)
+    if o.no_osd == 1 then
+        return
+    end
     if o.custom_header and o.custom_header ~= "" then
         s.header = set_ASS(true) .. o.custom_header
     else
@@ -161,6 +186,9 @@ end
 
 
 function no_ASS(t)
+    if o.no_osd == 1 then
+        return t
+    end
     return set_ASS(false) .. t .. set_ASS(true)
 end
 
@@ -176,13 +204,13 @@ end
 
 
 function b(t)
-    return "{\\b1}" .. t .. "{\\b0}"
+    return o.b1 .. t .. o.b0
 end
 function i(t)
-    return "{\\i1}" .. t .. "{\\i0}"
+    return o.i1 .. t .. o.i0
 end
 function u(t)
-    return "{\\u1}" .. t .. "{\\u0}"
+    return o.u1 .. t .. o.u0
 end