How can I obtain the bitrate of a video from a command line in Linux?

ffmpeg works fine:

ffmpeg -i file.avi

You can use MPlayer to get that information.

$ mplayer -vo null -ao null -identify -frames 0 foo.avi

In particular, you want the -identify option. The option -frames 0 tells it not to playback the file, and -vo null -ao null give it null drivers for video & audio (so you can use this command via SSH or another non-X-enabled terminal).

You can combine this with grep or other tools to pull out the specific line you want:

$ mplayer -vo null -ao null -identify -frames 0 foo.avi | grep kbps
VIDEO:  [XVID]  512x384  24bpp  29.970 fps  990.9 kbps (121.0 kbyte/s)

The full output looks like this:

$ mplayer -vo null -ao null -identify -frames 0 foo.avi
MPlayer dev-SVN-r26940 (C) 2000-2007 MPlayer Team
CPU: [hw dependent]
CPUflags:  [hw dependent]
Compiled with runtime CPU detection.

Playing foo.avi.
AVI file format detected.
ID_VIDEO_ID=0
[aviheader] Video stream found, -vid 0
ID_AUDIO_ID=1
[aviheader] Audio stream found, -aid 1
VIDEO:  [XVID]  512x384  24bpp  29.970 fps  990.9 kbps (121.0 kbyte/s)
Clip info:
 Software: transcode-1.0.2
ID_CLIP_INFO_NAME0=Software
ID_CLIP_INFO_VALUE0=transcode-1.0.2
ID_CLIP_INFO_N=1
ID_FILENAME=foo.avi
ID_DEMUXER=avi
ID_VIDEO_FORMAT=XVID
ID_VIDEO_BITRATE=990928
ID_VIDEO_WIDTH=512
ID_VIDEO_HEIGHT=384
ID_VIDEO_FPS=29.970
ID_VIDEO_ASPECT=0.0000
ID_AUDIO_FORMAT=85
ID_AUDIO_BITRATE=135104
ID_AUDIO_RATE=0
ID_AUDIO_NCH=0
ID_LENGTH=1288.95
ID_SEEKABLE=1
==========================================================================
Opening video decoder: [ffmpeg] FFmpeg's libavcodec codec family
Selected video codec: [ffodivx] vfm: ffmpeg (FFmpeg MPEG-4)
==========================================================================
ID_VIDEO_CODEC=ffodivx
==========================================================================
Opening audio decoder: [mp3lib] MPEG layer-2, layer-3
AUDIO: 48000 Hz, 2 ch, s16le, 128.0 kbit/8.33% (ratio: 16000->192000)
ID_AUDIO_BITRATE=128000
ID_AUDIO_RATE=48000
ID_AUDIO_NCH=2
Selected audio codec: [mp3] afm: mp3lib (mp3lib MPEG layer-2, layer-3)
==========================================================================
AO: [null] 48000Hz 2ch s16le (2 bytes per sample)
ID_AUDIO_CODEC=mp3
Starting playback...

Exiting... (End of file)

avprobe -show_streams file.avi