Subtitles: Prefer text-based options when available

As we know, the roku video player does not support image-based
subtitles, so any attempt to play these results in transcoding.

As this is undesirable, this patch modifies the default subtitle
logic to prefer any text-based subtitles that match their user's
preference. If no such text-based subtitles exist, we then allow
image-based subtitles to be selected.

source/utils/Subtitles.brs

@@ -4,34 +4,43 @@ function defaultSubtitleTrackFromVid(video_id) as integer
     meta = ItemMetaData(video_id)
     if meta = invalid then return invalid
     subtitles = sortSubtitles(meta.id, meta.json.MediaSources[0].MediaStreams)
-    return defaultSubtitleTrack(subtitles["all"]) ' Find correct subtitle track
+    default_text_subs = defaultSubtitleTrack(subtitles["all"], true) ' Find correct subtitle track (forced text)
+    if default_text_subs <> -1
+        return default_text_subs
+    else
+        return defaultSubtitleTrack(subtitles["all"]) ' if no appropriate text subs exist, allow non-text
+    end if
 end function
 
 
-' Identify the defaulty subtitle track
+' Identify the default subtitle track
+' if "requires_text" is true, only return a track if it is textual
+'     This allows forcing text subs, since roku requires transcoding of non-text subs
 ' returns the server-side track index for the appriate subtitle
-function defaultSubtitleTrack(sorted_subtitles) as integer
+function defaultSubtitleTrack(sorted_subtitles, require_text = false) as integer
     if m.user.Configuration.SubtitleMode = "None"
         return -1 ' No subtitles desired: select none
     end if
 
     for each item in sorted_subtitles
-        if m.user.Configuration.SubtitleMode = "Default" and (item.isForced or item.IsDefault or item.IsExternal)
-            return item.Index ' Finds first forced, or default, or external subs in sorted list
-        else if m.user.Configuration.SubtitleMode = "Always" and not item.IsForced
-            return item.Index ' Select the first non-forced subtitle option in the sorted list
-        else if m.user.Configuration.SubtitleMode = "OnlyForced" and item.IsForced
-            return item.Index ' Select the first forced subtitle option in the sorted list
-        else if m.user.Configuration.SubtitlePlaybackMode = "Smart" and (item.isForced or item.IsDefault or item.IsExternal)
-            ' Simplified "Smart" logic here mimics Default (as that is fallback behavior normally)
-            ' Avoids detecting preferred audio language (as is utilized in main client)
-            return item.Index
+        if (require_text and item.IsTextSubtitleStream) or not require_text
+            if m.user.Configuration.SubtitleMode = "Default" and (item.isForced or item.IsDefault or item.IsExternal)
+                return item.Index ' Finds first forced, or default, or external subs in sorted list
+            else if m.user.Configuration.SubtitleMode = "Always" and not item.IsForced
+                return item.Index ' Select the first non-forced subtitle option in the sorted list
+            else if m.user.Configuration.SubtitleMode = "OnlyForced" and item.IsForced
+                return item.Index ' Select the first forced subtitle option in the sorted list
+            else if m.user.Configuration.SubtitlePlaybackMode = "Smart" and (item.isForced or item.IsDefault or item.IsExternal)
+                ' Simplified "Smart" logic here mimics Default (as that is fallback behavior normally)
+                ' Avoids detecting preferred audio language (as is utilized in main client)
+                return item.Index
+            end if
         end if
     end for
     return -1 ' Keep current default behavior of "None", if no correct subtitle is identified
 end function
 
-' The subtitle index on the server differes from the index we track locally
+' The subtitle index on the server differs from the index we track locally
 ' This function converts the former into the latter
 function getSubtitleSelIdxFromSubIdx(subtitles, sub_idx) as integer
     selIdx = 0