I'm not really well versed in the command line so hopefully this isn't too stupid of a question.

If I run:

ffmpeg -i videofile.avi

I get an output such as this:

ffmpeg version git-2013-11-21-6a7980e Copyright (c) 2000-2013 the FFmpeg develop    ers

  built on Nov 21 2013 12:06:32 with gcc 4.6 (Ubuntu/Linaro 4.6.3-1ubuntu5)

  configuration: --prefix=/home/user/ffmpeg_build --extra-cflags=-I/home/user/ffmpeg_build/include --extra-ldflags=-L/home/user/ffmpeg_build/lib --b        indir=/home/user/bin --extra-libs=-ldl --enable-gpl --enable-libass --enable    -libfdk-    aac --enable-libmp3lame --enable-libtheora --enable-libvorbis --enable-l    ibx264 --enable-    nonfree

  libavutil      52. 53.100 / 52. 53.100

  libavcodec     55. 44.100 / 55. 44.100

  libavformat    55. 21.100 / 55. 21.100

  libavdevice    55.  5.100 / 55.  5.100

  libavfilter     3. 91.100 /  3. 91.100

  libswscale      2.  5.101 /  2.  5.101

  libswresample   0. 17.104 /  0. 17.104

  libpostproc    52.  3.100 / 52.  3.100

Input #0, avi, from 'videofile.avi':

  Metadata:

    encoder         : Lavf52.68.0

  Duration: 00:23:07.68, start: 0.000000, bitrate: 2390 kb/s

    Stream #0:0: Video: mpeg4 (Simple Profile) (XVID / 0x44495658), yuv420p, 640x480     [SAR 1:1 DAR 4:3], 23.98 fps, 23.98 tbr, 23.98 tbn, 1199 tbc

    Stream #0:1: Audio: mp3 (U[0][0][0] / 0x0055), 44100 Hz, stereo, s16p, 128 k    b/s

If I were only interested in the command outputting "640x480", how might I do that?

I imagine I have to pipe the output to, and perform, a regular expression? No idea how to do that. Thanks!