avoid hang if the user specified non-existent preset

videoclip.lua

@@ -31,6 +31,18 @@ local encoder
 local OSD
 local Timings
 
+local presets = {
+    ultrafast = true,
+    superfast = true,
+    veryfast = true,
+    faster = true,
+    fast = true,
+    medium = true,
+    slow = true,
+    slower = true,
+    veryslow = true,
+}
+
 ------------------------------------------------------------
 -- utility functions
 
@@ -335,6 +347,10 @@ if not config.audio_bitrate:endswith('k') then
     config.audio_bitrate = config.audio_bitrate .. 'k'
 end
 
+if not presets[config.preset] then
+    config.preset = 'faster'
+end
+
 ------------------------------------------------------------
 -- Finally, set an 'entry point' in mpv