Update ffmpeg.md

if so → and

pages/common/ffmpeg.md

@@ -26,6 +26,6 @@
 
 `ffmpeg -i {{input_video}}.mkv -codec copy {{output_video}}.mp4`
 
-- Convert MP4 video to VP9 codec. For the best quality, use a CRF value (recommended range 15-35) if so, -b:video MUST be 0:
+- Convert MP4 video to VP9 codec. For the best quality, use a CRF value (recommended range 15-35) and -b:video MUST be 0:
 
 `ffmpeg -i {{input_video}}.mp4 -codec:video libvpx-vp9 -crf {{30}} -b:video 0 -codec:audio libopus -vbr on -threads {{number_of_threads}} {{output_video}}.webm`