ffmpeg on openwrt

With mjpg-streamer running - proves that video is occupied (which proves the next one is reading video?):

root@OpenWrt:/# ffmpeg -f video4linux2 -i /dev/video0 /tmp/video.avi
ffmpeg version 0.8.7, Copyright (c) 2000-2011 the FFmpeg developers
  built on Apr  6 2012 12:10:35 with gcc 4.6.3 20120201 (prerelease)
  configuration: --enable-cross-compile --cross-prefix=mips-openwrt-linux-uclibc- --arch=mips --target-os=linux --prefix=/usr --enable-shared --enable-static --disable-debug --pkg-config=pkg-config --enable-gpl --enable-version3 --disable-asm --disable-doc --disable-dxva2 --enable-pthreads --disable-optimizations --enable-small --disable-stripping --enable-zlib
  libavutil    51.  9. 1 / 51.  9. 1
  libavcodec   53.  8. 0 / 53.  8. 0
  libavformat  53.  5. 0 / 53.  5. 0
  libavdevice  53.  1. 1 / 53.  1. 1
  libavfilter   2. 23. 0 /  2. 23. 0
  libswscale    2.  0. 0 /  2.  0. 0
  libpostproc  51.  2. 0 / 51.  2. 0
[video4linux2 @ 0xb8f410] ioctl(VIDIOC_REQBUFS)
/dev/video0: Input/output error



Without mjpg-streamer running:
root@OpenWrt:/# ffmpeg -f video4linux2 -i /dev/video0 /tmp/video.avi
ffmpeg version 0.8.7, Copyright (c) 2000-2011 the FFmpeg developers
  built on Apr  6 2012 12:10:35 with gcc 4.6.3 20120201 (prerelease)
  configuration: --enable-cross-compile --cross-prefix=mips-openwrt-linux-uclibc- --arch=mips --target-os=linux --prefix=/usr --enable-shared --enable-static --disable-debug --pkg-config=pkg-config --enable-gpl --enable-version3 --disable-asm --disable-doc --disable-dxva2 --enable-pthreads --disable-optimizations --enable-small --disable-stripping --enable-zlib
  libavutil    51.  9. 1 / 51.  9. 1
  libavcodec   53.  8. 0 / 53.  8. 0
  libavformat  53.  5. 0 / 53.  5. 0
  libavdevice  53.  1. 1 / 53.  1. 1
  libavfilter   2. 23. 0 /  2. 23. 0
  libswscale    2.  0. 0 /  2.  0. 0
  libpostproc  51.  2. 0 / 51.  2. 0
^C
root@OpenWrt:/# ls /tmp
TZ                log               overlay           run
dhcp.leases       luci-indexcache   pipe              state
etc               luci-modulecache  resolv.conf
lock              luci-sessions     resolv.conf.auto
root@OpenWrt:/#