$ ffmpeg  -i s.flv -an -vcodec libx264 -crf 20 -b 888k -vf crop=760:420:260:100 -s 380x210 s2before.flv
ffmpeg version 0.10 Copyright (c) 2000-2012 the FFmpeg developers
  built on Apr 29 2012 20:41:33 with gcc 4.6.1
  configuration: --enable-gpl --enable-libfaac --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libtheora --enable-libvorbis --enable-libvpx --enable-nonfree --enable-version3 --enable-x11grab --enable-libspeex --enable-libx264
  libavutil      51. 34.101 / 51. 34.101
  libavcodec     53. 60.100 / 53. 60.100
  libavformat    53. 31.100 / 53. 31.100
  libavdevice    53.  4.100 / 53.  4.100
  libavfilter     2. 60.100 /  2. 60.100
  libswscale      2.  1.100 /  2.  1.100
  libswresample   0.  6.100 /  0.  6.100
  libpostproc    52.  0.100 / 52.  0.100
[libspeex @ 0x19fdf20] Missing Speex header, assuming defaults.
Input #0, flv, from 's.flv':
  Metadata:
    encoder         : Lavf53.31.100
  Duration: 00:00:12.26, start: 0.010000, bitrate: 1054 kb/s
    Stream #0:0: Video: h264 (High), yuv420p, 1280x720, 30 tbr, 1k tbn, 2k tbc
    Stream #0:1: Audio: speex, 16000 Hz, 1 channels, s16
Please use -b:a or -b:v, -b is ambiguous
File 's2before.flv' already exists. Overwrite ? [y/N] y
w:1280 h:720 pixfmt:yuv420p tb:1/1000000 sar:0/1 sws_param:
[scale @ 0x1a08ce0] w:1280 h:720 fmt:yuv420p -> w:380 h:210 fmt:yuv420p flags:0x4
[crop @ 0x1a09480] w:380 h:210 -> w:760 h:420
[crop @ 0x1a09480] Invalid too big or non positive size for width '760' or height '420'
Error opening filters!