mkfifo temp1.v
mkfifo temp2.v
mkfifo temp1.a

ffmpeg -i resident\ evil\ 4\ pre-release\ trailer.wmv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - >temp1.a </dev/null
ffmpeg -i resident\ evil\ 4\ pre-release\ trailer.wmv -an -f yuv4mpegpipe - >temp1.v </dev/null
ffmpeg -f rawvideo -pix_fmt rgb24 -s 460x380 -r 30000/1001 -t 00:10:00 -i /dev/zero -f yuv4mpegpipe -pix_fmt yuv420p - >temp2.v </dev/null
cat temp1.v temp2.v >all.v
ffmpeg -f u16le -acodec pcm s16le -ac 2 -ar 44100 -i temp1.a -f yuv4mpegpipe -i all.v output.flv

[1]   Done                    ffmpeg -i resident\ evil\ 4\ pre-release\ trailer.wmv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - >temp1.a </dev/null
[2]   Done                    ffmpeg -i resident\ evil\ 4\ pre-release\ trailer.wmv -an -f yuv4mpegpipe - >temp1.v </dev/null
[3]-  Broken pipe             ffmpeg -f rawvideo -pix_fmt rgb24 -s 460x380 -r 30000/1001 -t 00:10:00 -i /dev/zero -f yuv4mpegpipe -pix_fmt yuv420p - >temp2.v </dev/null
[4]+  Broken pipe             cat temp1.v temp2.v >all.v