I want to extract video frames and save them as image.

```
import os, sys
from PIL import Image

a, b, c = os.popen3("ffmpeg -i test.avi")
out = c.read()
dp = out.index("Duration: ")
duration = out[dp+10:dp+out[dp:].index(",")]
hh, mm, ss = map(float, duration.split(":"))
total = (hh*60 + mm)*60 + ss
for i in xrange(9):
    t = (i + 1) * total / 10
    os.system("ffmpeg -i test.avi -ss %0.3fs frame%i.png" % (t, i))

```

But I have this error:

```
FFmpeg version CVS, Copyright (c) 2000-2004 Fabrice Bellard
Mac OSX universal build for ffmpegX
  configuration:  --enable-memalign-hack --enable-mp3lame --enable-gpl --disable-vhook --disable-ffplay --disable-ffserver --enable-a52 --enable-xvid --enable-faac --enable-faad --enable-amr_nb --enable-amr_wb --enable-pthreads --enable-x264 
  libavutil version: 49.0.0
  libavcodec version: 51.9.0
  libavformat version: 50.4.0
  built on Apr 15 2006 04:58:19, gcc: 4.0.1 (Apple Computer, Inc. build 5250)
Input #0, avi, from 'test.avi':
  Duration: 00:00:30.5, start: 0.000000, bitrate: 465 kb/s
  Stream #0.0, 25.00 fps(r): Video: mpeg4, yuv420p, 640x480
  Stream #0.1: Audio: mp3, 32000 Hz, mono, 32 kb/s
Unable for find a suitable output format for 'frame0.png'

```

Edit: ffmpeg -formats

```
FFmpeg version CVS, Copyright (c) 2000-2004 Fabrice Bellard
Mac OSX universal build for ffmpegX
  configuration:  --enable-memalign-hack --enable-mp3lame --enable-gpl --disable-vhook --disable-ffplay --disable-ffserver --enable-a52 --enable-xvid --enable-faac --enable-faad --enable-amr_nb --enable-amr_wb --enable-pthreads --enable-x264 
  libavutil version: 49.0.0
  libavcodec version: 51.9.0
  libavformat version: 50.4.0
  built on Apr 15 2006 04:58:19, gcc: 4.0.1 (Apple Computer, Inc. build 5250)
File formats:
  E 3g2             3gp2 format
  E 3gp             3gp format
 D  4xm             4X Technologies format
 D  RoQ             Id RoQ format
 D  aac             ADTS AAC
 DE ac3             raw ac3
  E adts            ADTS AAC
 DE aiff            Audio IFF
 DE alaw            pcm A law format
 DE amr             3gpp amr file format
 DE asf             asf format
  E asf_stream      asf format
 DE au              SUN AU Format
 DE avi             avi format
 D  avs             avs format
  E crc             crc testing format
 D  daud            D-Cinema audio format
 D  dts             raw dts
 DE dv              DV video format
  E dvd             MPEG2 PS format (DVD VOB)
 D  ea              Electronic Arts Multimedia Format
 DE ffm             ffm format
 D  film_cpk        Sega FILM/CPK format
 D  flic            FLI/FLC/FLX animation format
 DE flv             flv format
  E framecrc        framecrc testing format
 DE gif             GIF Animation
 DE h261            raw h261
 DE h263            raw h263
 DE h264            raw H264 video format
 D  idcin           Id CIN format
 DE image           image sequence
 DE image2          image2 sequence
 DE image2pipe      piped image2 sequence
 DE imagepipe       piped image sequence
 D  ingenient       Ingenient MJPEG
 D  ipmovie         Interplay MVE format
 DE m4v             raw MPEG4 video format
 D  matroska        Matroska file format
 DE mjpeg           MJPEG video
 D  mm              American Laser Games MM format
 DE mmf             mmf format
  E mov             mov format
 D  mov,mp4,m4a,3gp,3g2,mj2 QuickTime/MPEG4/Motion JPEG 2000 format
  E mp2             MPEG audio layer 2
 DE mp3             MPEG audio layer 3
  E mp4             mp4 format
 DE mpeg            MPEG1 System format
  E mpeg1video      MPEG video
  E mpeg2video      MPEG2 video
 DE mpegts          MPEG2 transport stream format
 D  mpegvideo       MPEG video
  E mpjpeg          Mime multipart JPEG format
 DE mulaw           pcm mu law format
 D  nsv             NullSoft Video format
  E null            null video format
 DE nut             nut format
 D  nuv             NuppelVideo format
 D  ogg             Ogg
  E psp             psp mp4 format
 D  psxstr          Sony Playstation STR format
 DE rawvideo        raw video format
 D  redir           Redirector format
 DE rm              rm format
  E rtp             RTP output format
 D  rtsp            RTSP input format
 DE s16be           pcm signed 16 bit big endian format
 DE s16le           pcm signed 16 bit little endian format
 DE s8              pcm signed 8 bit format
 D  sdp             SDP
 D  shn             raw shorten
 D  smk             Smacker Video
 D  sol             Sierra SOL Format
  E svcd            MPEG2 PS format (VOB)
 DE swf             Flash format
 D  tta             true-audio
 DE u16be           pcm unsigned 16 bit big endian format
 DE u16le           pcm unsigned 16 bit little endian format
 DE u8              pcm unsigned 8 bit format
  E vcd             MPEG1 System format (VCD)
 D  vmd             Sierra VMD format
  E vob             MPEG2 PS format (VOB)
 DE voc             Creative Voice File format
 DE wav             wav format
 D  wc3movie        Wing Commander III movie format
 D  wsaud           Westwood Studios audio format
 D  wsvqa           Westwood Studios VQA format
 DE yuv4mpegpipe    YUV4MPEG pipe format

Image formats (filename extensions, if any, follow):
 DE gif    gif

Codecs:
 D V    4xm
 D V D  8bps
 DEA    aac
 D V D  aasc
 DEA    ac3
 DEA    adpcm_4xm
 DEA    adpcm_adx
 DEA    adpcm_ct
 DEA    adpcm_ea
 DEA    adpcm_ima_dk3
 DEA    adpcm_ima_dk4
 DEA    adpcm_ima_qt
 DEA    adpcm_ima_smjpeg
 DEA    adpcm_ima_wav
 DEA    adpcm_ima_ws
 DEA    adpcm_ms
 DEA    adpcm_sbpro_2
 DEA    adpcm_sbpro_3
 DEA    adpcm_sbpro_4
 DEA    adpcm_swf
 DEA    adpcm_xa
 DEA    adpcm_yamaha
 D A    alac
 DEA    amr_nb
 DEA    amr_wb
 DEV D  asv1
 DEV D  asv2
 D V D  avs
 D V    bmp
 D V D  camstudio
 D V D  camtasia
 D V D  cinepak
 D V D  cljr
 D A    cook
 D V D  cyuv
 DES    dvbsub
 DES    dvdsub
 DEV D  dvvideo
 DEV D  ffv1
 DEVSD  ffvhuff
 D A    flac
 D V D  flic
 DEVSD  flv
 D V D  fraps
 DEA    g726
 DEV D  h261
 DEVSDT h263
 D VSD  h263i
  EV    h263p
 DEV DT h264
 DEVSD  huffyuv
 D V D  idcinvideo
 D V D  indeo2
 D V    indeo3
 D A    interplay_dpcm
 D V D  interplayvideo
  EV    jpegls
 D V    kmvc
  EV    ljpeg
 D V D  loco
 D A    mace3
 D A    mace6
 D V D  mdec
 DEV D  mjpeg
 D V D  mjpegb
 D V D  mmvideo
 DEA    mp2
 DEA    mp3
 D A    mp3adu
 D A    mp3on4
 DEVSDT mpeg1video
 DEVSDT mpeg2video
 DEVSDT mpeg4
 D A    mpeg4aac
 D VSDT mpegvideo
 DEVSD  msmpeg4
 DEVSD  msmpeg4v1
 DEVSD  msmpeg4v2
 D V D  msrle
 D V D  msvideo1
 D V D  mszh
 D V D  nuv
 DEV    pam
 DEV    pbm
 DEA    pcm_alaw
 DEA    pcm_mulaw
 DEA    pcm_s16be
 DEA    pcm_s16le
 DEA    pcm_s24be
 DEA    pcm_s24daud
 DEA    pcm_s24le
 DEA    pcm_s32be
 DEA    pcm_s32le
 DEA    pcm_s8
 DEA    pcm_u16be
 DEA    pcm_u16le
 DEA    pcm_u24be
 DEA    pcm_u24le
 DEA    pcm_u32be
 DEA    pcm_u32le
 DEA    pcm_u8
 DEV    pgm
 DEV    pgmyuv
 DEV    png
 DEV    ppm
 D A    qdm2
 D V D  qdraw
 D V D  qpeg
 D V D  qtrle
 DEV    rawvideo
 D A    real_144
 D A    real_288
 D A    roq_dpcm
 D V D  roqvideo
 D V D  rpza
 DEV D  rv10
 DEV D  rv20
 D A    shorten
 D A    smackaud
 D V    smackvid
 D V D  smc
 DEV    snow
 D A    sol_dpcm
 DEA    sonic
  EA    sonicls
 D V D  sp5x
 DEV D  svq1
 D VSD  svq3
 D V    theora
 D V D  truemotion1
 D V D  truemotion2
 D A    truespeech
 D A    tta
 D V D  ultimotion
 D V    vc9
 D V D  vcr1
 D A    vmdaudio
 D V D  vmdvideo
 D A    vorbis
 D V    vp3
 D V D  vqavideo
 D A    wmav1
 D A    wmav2
 DEVSD  wmv1
 DEVSD  wmv2
 D V D  wnv1
 D A    ws_snd1
 D A    xan_dpcm
 D V D  xan_wc3
 D V D  xl
  EV    xvid
 DEV D  zlib
 D V    zmbv

Supported file protocols:
 file: pipe: udp: rtp: tcp: http:
Frame size, frame rate abbreviations:
 ntsc pal qntsc qpal sntsc spal film ntsc-film sqcif qcif cif 4cif
Motion estimation methods:
 zero(fastest) full(slowest) log phods epzs(default) x1 hex umh iter

Note, the names of encoders and decoders dont always match, so there are
several cases where the above table shows encoder only or decoder only entries
even though both encoding and decoding are supported for example, the h263
decoder corresponds to the h263 and h263p encoders, for file formats its even
worse

```

What is wrong in my code? Thanks in advance