prboom-plus -timedemo BT01-009 -viddump

cap_soundcommand "ffmpeg -f s16le -ar %s -ac 2 -i pipe:0 -acodec libvorbis -aq 5 temp1.ogg"
cap_videocommand "ffmpeg -f rawvideo -pix_fmt rgb24 -s %wx%h -r 35 -i pipe:0 -vcodec libvpx -b:v 200k temp2.webm"
cap_muxcommand "ffmpeg -i temp1.ogg -i temp2.webm -vcodec copy -acodec copy %f.webm"
cap_tempfile1 "temp1.ogg"
cap_tempfile2 "temp2.webm"
cap_remove_tempfiles 1