2出力にすればできる（試してない
ffmpeg.exe -rtbufsize 256MB -r 30 -f dshow
-i video="SCFF DirectShow Filter":audio="ライン入力 (Realtek High Definition "
-c:v h264_qsv -threads 0 -r 30 -s 640x480 -sws_flags accurate_rnd+lanczos
-pix_fmt yuv420p -b:v 300k -bufsize 600k -preset veryslow -profile:v main
-acodec libfdk_aac -profile:a aac_he_v2 -ar 48000 -ab 32k -ac 2
-f flv "rtmp://localhost/live/livestream"
-c:v h264_qsv -threads 0 -r 30 -s 640x480 -sws_flags accurate_rnd+lanczos
-pix_fmt yuv420p -b:v 2000k -bufsize 4000k -preset veryslow -profile:v main
-acodec libfdk_aac -profile:a aac_he_v2 -ar 48000 -ab 32k -ac 2
output.mp4"