diff --git a/videoclip.lua b/videoclip.lua
index 137c6aa..151b1c1 100644
--- a/videoclip.lua
+++ b/videoclip.lua
@@ -46,10 +46,6 @@ local allowed_presets = {
 ------------------------------------------------------------
 -- Utility functions
 
-function string:endswith(suffix)
-    return suffix == "" or self:sub(-#suffix) == suffix
-end
-
 local function remove_extension(filename)
     return filename:gsub('%.%w+$', '')
 end
@@ -135,6 +131,22 @@ local function set_video_settings()
     end
 end
 
+local function validate_config()
+    if not config.audio_bitrate:match('^%d+[kK]$') then
+        config.audio_bitrate = (tonumber(config.audio_bitrate) or 32) .. 'k'
+    end
+
+    if not config.video_bitrate:match('^%d+[kKmM]$') then
+        config.video_bitrate = '1M'
+    end
+
+    if not allowed_presets[config.preset] then
+        config.preset = 'faster'
+    end
+
+    set_video_settings()
+end
+
 ------------------------------------------------------------
 -- Provides interface for creating audio/video clips
 
@@ -479,20 +491,8 @@ function Timings:validate()
     return self['start'] >= 0 and self['start'] < self['end']
 end
 
-------------------------------------------------------------
--- Validate config
-
-if not config.audio_bitrate:endswith('k') then
-    config.audio_bitrate = config.audio_bitrate .. 'k'
-end
-
-if not allowed_presets[config.preset] then
-    config.preset = 'faster'
-end
-
-set_video_settings()
-
 ------------------------------------------------------------
 -- Finally, set an 'entry point' in mpv
 
+validate_config()
 mp.add_key_binding('c', 'videoclip-menu-open', main_menu.open)