ffmpeg error

$ ffmpeg -v verbose -r 10 -s 320x240 -f video4linux2 -i /dev/video0 http://host.com:8090/webcam.ffm
ffmpeg version N-62569-gf57ac37 Copyright (c) 2000-2014 the FFmpeg developers
  built on Apr 20 2014 02:07:21 with gcc 4.7 (Ubuntu/Linaro 4.7.2-2ubuntu1)
  configuration: --prefix=/mnt/storeage --enable-libv4l2
  libavutil      52. 77.100 / 52. 77.100
  libavcodec     55. 58.105 / 55. 58.105
  libavformat    55. 37.101 / 55. 37.101
  libavdevice    55. 13.100 / 55. 13.100
  libavfilter     4.  4.100 /  4.  4.100
  libswscale      2.  6.100 /  2.  6.100
  libswresample   0. 18.100 /  0. 18.100
[video4linux2,v4l2 @ 0x287bc20] fd:3 capabilities:4000001
[video4linux2,v4l2 @ 0x287bc20] The driver changed the time per frame from 1/10 to 1/15
Input #0, video4linux2,v4l2, from '/dev/video0':
  Duration: N/A, start: 149734.341256, bitrate: 18432 kb/s
    Stream #0:0: Video: rawvideo (YUY2 / 0x32595559), yuyv422, 320x240, 18432 kb/s, 15 fps, 15 tbr, 1000k tbn, 1000k tbc
Incompatible pixel format '(null)' for codec 'mjpeg', auto-selecting format '(null)'
[graph 0 input from stream 0:0 @ 0x286a7e0] w:320 h:240 pixfmt:yuyv422 tb:1/10 fr:10/1 sar:0/1 sws_param:flags=2
[scaler for output stream 0:0 @ 0x286ac00] w:0 h:15 flags:'0x4' interl:0
Incompatible pixel format '(null)' for codec 'mjpeg', auto-selecting format '(null)'
[graph 0 input from stream 0:0 @ 0x286a7e0] TB:0.100000 FRAME_RATE:10.000000 SAMPLE_RATE:nan
[scaler for output stream 0:0 @ 0x286ac00] w:320 h:240 fmt:yuyv422 sar:0/1 -> w:320 h:15 fmt:yuyv422 sar:0/1 flags:0x4
[mjpeg @ 0x2883180] Specified pixel format yuyv422 is invalid or not supported
Output #0, ffm, to 'http://host.com:8090/webcam.ffm':
  Metadata:
    creation_time   : now
    Stream #0:0: Video: mjpeg ([0][0][0][5] / 0x5000000), yuyv422, 320x15, q=0-0, 20000 kb/s, 1000k tbn, 10 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo -> mjpeg)
Error while opening encoder for output stream #0:0 - maybe incorrect parameters such as bit_rate, rate, width or height