add ability to set fps from the config file

refer to #7

README.md

@@ -102,6 +102,9 @@ video_quality=23
 # Use the slowest preset that you have patience for.
 # https://trac.ffmpeg.org/wiki/Encode/H.264
 preset=faster
+# FPS / framerate. Set to "auto" or a number.
+video_fps=auto
+video_fps=60
 
 # Audio settings
 # Available formats: opus or aac

videoclip.lua

@@ -40,6 +40,7 @@ local config = {
     video_bitrate = '1M',
     video_width = -2,
     video_height = 480,
+    video_fps = 'auto',
     audio_format = 'opus', -- aac, opus
     audio_bitrate = '32k', -- 32k, 64k, 128k, 256k. aac requires higher bitrates.
     font_size = 24,
@@ -245,6 +246,10 @@ encoder.mkargs_video = function(clip_filename)
         table.concat { '-o=', clip_path }
     }
 
+    if config.video_fps ~= 'auto' then
+        table.insert(args, #args, table.concat { '--vf-add=fps=', config.video_fps })
+    end
+
     if mp.get_property_bool("sub-visibility") == true then
         args = encoder.append_embed_subs_args(args)
     end