Install USB sound card:

http://www.ibuyopenwrt.com/index.php/8-yun-compatible/62-usb-sound-card

opkg update
opkg install alsa-utils
opkg install ffmpeg
opkg install lame-lib
arecord -l
**** List of CAPTURE Hardware Devices ****
card 0: Set [C-Media USB Headphone Set], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
ffmpeg  -y -f alsa -acodec pcm_s16le -ac 1 -ar 44100 -i hw:0,0,0 -t 60 -acodec mp2 /mnt/sda1/output.mp3
nano  record.sh
#!/bin/ash
ffmpeg  -y -f alsa -acodec pcm_s16le -ac 1 -ar 44100 -i hw:0,0,0 -t 60 -acodec mp2 /mnt/sda1/output.mp3 > /dev/null 2>&1