/ffmpeg -f avfoundation -framerate 30 -pixel_format yuyv422 -probesize 10M -i "1:0" -f avfoundation -framerate 30 -pixel_format yuyv422 -probesize 10M -i "0" -filter_complex 'overlay=10:main_h-overlay_h-10' -vcodec libx264 -b:v 800k -r:v 25 -s 1280x720 -preset ultrafast out.avi
./ffmpeg -f avfoundation -pix_fmt yuyv422 -framerate 30 -probesize 10M -thread_queue_size 512 -i "1:0" -f avfoundation -pix_fmt yuyv422 -framerate 30 -probesize 10M -thread_queue_size 512 -i "0" -filter_complex 'overlay=10:main_h-overlay_h-10' -vcodec libx264 -b:v 800k -r:v 25 -s 1280x720 -preset ultrafast -y -f flv test.flv
./ffmpeg -f avfoundation -pix_fmt yuyv422 -framerate 30 -probesize 10M -thread_queue_size 512 -i "1:0" -f avfoundation -pix_fmt yuyv422 -framerate 30 -probesize 10M -thread_queue_size 512 -i "0" -filter_complex 'overlay=main_w-overlay_w-10:main_h-overlay_h-10' -vcodec libx264 -b:v 800k -r:v 25 -s 1280x720 -preset ultrafast -y -f flv test.flv
./ffmpeg -f avfoundation -pix_fmt yuyv422 -framerate 30 -probesize 10M -thread_queue_size 512 -i "1:0" -f avfoundation -pix_fmt yuyv422 -framerate 30 -probesize 10M -thread_queue_size 512 -i "0" -filter_complex 'overlay=W-w:H-h' -vcodec libx265 -b:v 800k -r:v 25 -s 1440x900 -preset ultrafast -acodec aac -reconnect 99999 -y -f mp4 test.mp4
./ffmpeg -f avfoundation -pix_fmt yuyv422 -framerate 30 -probesize 10M -thread_queue_size 512 -i "1:0" -f avfoundation -pix_fmt yuyv422 -framerate 30 -probesize 10M -thread_queue_size 512 -i "0" -filter_complex 'overlay=W-w:H-h' -vcodec h264_videotoolbox -b:v 800k -r:v 25 -s 1440x900 -preset ultrafast -acodec aac_at -reconnect 99999 -y -f mp4 test.mp4
参考：
http://blog.chinaunix.net/uid-11344913-id-4665455.html
https://trac.ffmpeg.org/wiki/HWAccelIntro
http://www.cnblogs.com/wainiwann/p/4031129.html
