Try midentify.sh (TOOLS/midentify.sh in the source code tree of MPlayer).

It will show information in a parseable format:

$  ./midentify.sh /data/myvid.flv
ID_VIDEO_ID=0
ID_AUDIO_ID=1
ID_FILENAME=/data/myvid.flv
ID_DEMUXER=lavfpref
ID_VIDEO_FORMAT=VP6F
ID_VIDEO_BITRATE=0
ID_VIDEO_WIDTH=640
ID_VIDEO_HEIGHT=480

[,,,]

The good ol' "file" utility will often get the dimensions of a video file.

MediaInfo has a command line version and provides the dimensions together with tons of other information.

Use ffprobe (part of FFmpeg toolkit)

example:

ffprobe -v quiet -print_format json -show_format -show_streams ~/Movies/big_buck_bunny_720p_5mb.mp4

output:

{
"streams": [
{
"index": 0,
"codec_name": "h264",
"codec_long_name": "H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10",
"profile": "Main",
"codec_type": "video",
"codec_time_base": "1/50",
"codec_tag_string": "avc1",
"codec_tag": "0x31637661",
"width": 1280,
"height": 720,
"coded_width": 1280,
"coded_height": 720,
"has_b_frames": 0,
"sample_aspect_ratio": "1:1",
"display_aspect_ratio": "16:9",
"pix_fmt": "yuv420p",
"level": 31,
"chroma_location": "left",
"refs": 1,
"is_avc": "1",
"nal_length_size": "4",
"r_frame_rate": "25/1",
"avg_frame_rate": "25/1",
"time_base": "1/12800",
"start_pts": 0,
"start_time": "0.000000",
"duration_ts": 378368,
"duration": "29.560000",
"bit_rate": "1032960",
"bits_per_raw_sample": "8",
"nb_frames": "739",
"disposition": {
"default": 1,
"dub": 0,
"original": 0,
"comment": 0,
"lyrics": 0,
"karaoke": 0,
"forced": 0,
"hearing_impaired": 0,
"visual_impaired": 0,
"clean_effects": 0,
"attached_pic": 0
},
"tags": {
"creation_time": "1970-01-01 00:00:00",
"language": "und",
"handler_name": "VideoHandler"
}
},
{
"index": 1,
"codec_name": "aac",
"codec_long_name": "AAC (Advanced Audio Coding)",
"profile": "LC",
"codec_type": "audio",
"codec_time_base": "1/48000",
"codec_tag_string": "mp4a",
"codec_tag": "0x6134706d",
"sample_fmt": "fltp",
"sample_rate": "48000",
"channels": 6,
"channel_layout": "5.1",
"bits_per_sample": 0,
"r_frame_rate": "0/0",
"avg_frame_rate": "0/0",
"time_base": "1/48000",
"start_pts": 0,
"start_time": "0.000000",
"duration_ts": 1419264,
"duration": "29.568000",
"bit_rate": "383960",
"max_bit_rate": "416704",
"nb_frames": "1386",
"disposition": {
"default": 1,
"dub": 0,
"original": 0,
"comment": 0,
"lyrics": 0,
"karaoke": 0,
"forced": 0,
"hearing_impaired": 0,
"visual_impaired": 0,
"clean_effects": 0,
"attached_pic": 0
},
"tags": {
"creation_time": "1970-01-01 00:00:00",
"language": "und",
"handler_name": "SoundHandler"
}
}
],
"format": {
"filename": "/Users/farsheed/Movies/big_buck_bunny_720p_5mb.mp4",
"nb_streams": 2,
"nb_programs": 0,
"format_name": "mov,mp4,m4a,3gp,3g2,mj2",
"format_long_name": "QuickTime / MOV",
"start_time": "0.000000",
"duration": "29.568000",
"size": "5253880",
"bit_rate": "1421504",
"probe_score": 100,
"tags": {
"major_brand": "isom",
"minor_version": "512",
"compatible_brands": "isomiso2avc1mp41",
"creation_time": "1970-01-01 00:00:00",
"encoder": "Lavf53.24.2"
}
}
}

See documentation for more info.

Using exiftool

run the command

exiftool VIDEOFILE

The output you get is similar to this:

ExifTool Version Number         : 9.76
File Name                       : gource2.mkv
Directory                       : .
File Size                       : 2010 MB
File Modification Date/Time     : 2015:01:07 14:16:22-06:00
File Access Date/Time           : 2015:01:07 14:16:22-06:00
File Inode Change Date/Time     : 2015:01:07 14:16:22-06:00
File Permissions                : rw-rw-r--
File Type                       : MKV
MIME Type                       : video/x-matroska
EBML Version                    : 1
EBML Read Version               : 1
Doc Type                        : matroska
Doc Type Version                : 4
Doc Type Read Version           : 2
Timecode Scale                  : 1 ms
Muxing App                      : libebml v1.3.0 + libmatroska v1.4.1
Writing App                     : mkvmerge v7.4.0 ('Circles') 64bit built on Dec 17 2014 11:31:10
Duration                        : 2:35:09
Date/Time Original              : 2015:01:07 20:14:22Z
Video Codec ID                  : V_MPEG4/ISO/AVC
Video Frame Rate                : 60
Track Language                  : und
Image Width                     : 1280
Image Height                    : 1024
Display Width                   : 1280
Display Height                  : 1024
Track Number                    : 2
Track Type                      : Audio
Audio Codec ID                  : A_DTS
Default Duration                : 10.666666 ms
Audio Sample Rate               : 48000
Audio Channels                  : 6
Image Size                      : 1280x1024

Using ffmpeg/ffprobe

run the command

ffprobe VIDEOFILE

alternatively:

ffmpeg -i VIDEOFILE

The output you get is similar to this:

ffprobe version 2.1.6 Copyright (c) 2007-2014 the FFmpeg developers
built on Nov 29 2014 12:07:56 with gcc 4.8.3 (GCC) 20140911 (Red Hat 4.8.3-7)
configuration: --prefix=/usr --bindir=/usr/bin --datadir=/usr/share/ffmpeg --incdir=/usr/include/ffmpeg --libdir=/usr/lib64 --mandir=/usr/share/man --arch=x86_64 --optflags='-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic' --enable-bzlib --disable-crystalhd --enable-frei0r --enable-gnutls --enable-libass --enable-libcdio --enable-libcelt --enable-libdc1394 --disable-indev=jack --enable-libfreetype --enable-libgsm --enable-libmp3lame --enable-openal --enable-libopencv --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libvorbis --enable-libv4l2 --enable-libvpx --enable-libx264 --enable-libxvid --enable-x11grab --enable-avfilter --enable-avresample --enable-postproc --enable-pthreads --disable-static --enable-shared --enable-gpl --disable-debug --disable-stripping --shlibdir=/usr/lib64 --enable-runtime-cpudetect
libavutil      52. 48.101 / 52. 48.101
libavcodec     55. 39.101 / 55. 39.101
libavformat    55. 19.104 / 55. 19.104
libavdevice    55.  5.100 / 55.  5.100
libavfilter     3. 90.100 /  3. 90.100
libavresample   1.  1.  0 /  1.  1.  0
libswscale      2.  5.101 /  2.  5.101
libswresample   0. 17.104 /  0. 17.104
libpostproc    52.  3.100 / 52.  3.100
Input #0, matroska,webm, from 'gource2.mkv':
Metadata:
creation_time   : 2015-01-07 20:14:22
Duration: 02:35:09.70, start: 0.000000, bitrate: 1811 kb/s
Stream #0:0: Video: h264 (Constrained Baseline), yuv420p, 1280x1024, SAR 1:1 DAR 5:4, 60 fps, 60 tbr, 1k tbn, 120 tbc (default)
Stream #0:1(eng): Audio: dts (DTS), 48000 Hz, 5.1(side), fltp, 1536 kb/s (default)

Using mplayer

run the command

mplayer -really-quiet -ao null -vo null -identify -frames 0 VIDEOFILE

The output you get is similar to this:

ID_VIDEO_ID=0
ID_AUDIO_ID=0
ID_AID_0_LANG=eng
ID_CLIP_INFO_NAME0=creation_time
ID_CLIP_INFO_VALUE0=2015-01-07 20:14:22
ID_CLIP_INFO_N=1
ID_FILENAME=gource2.mkv
ID_DEMUXER=lavfpref
ID_VIDEO_FORMAT=H264
ID_VIDEO_BITRATE=0
ID_VIDEO_WIDTH=1280
ID_VIDEO_HEIGHT=1024
ID_VIDEO_FPS=60.000
ID_VIDEO_ASPECT=0.0000
ID_AUDIO_FORMAT=8193
ID_AUDIO_BITRATE=1536000
ID_AUDIO_RATE=48000
ID_AUDIO_NCH=6
ID_START_TIME=0.00
ID_LENGTH=9309.70
ID_SEEKABLE=1
ID_CHAPTERS=0
ID_VIDEO_CODEC=ffh264
ID_AUDIO_BITRATE=1536000
ID_AUDIO_RATE=48000
ID_AUDIO_NCH=6
ID_AUDIO_CODEC=ffdca
ID_EXIT=EOF

Using mediainfo

run the command

mediainfo VIDEOFILE

The output you get is similar to this:

General
Unique ID                                : 311795358270161665158539797930749663166 (0xEA919A09196F0CAEF4E1B4FEB72B17BE)
Complete name                            : gource2.mkv
Format                                   : Matroska
Format version                           : Version 4 / Version 2
File size                                : 1.96 GiB
Duration                                 : 2h 35mn
Overall bit rate                         : 1 811 Kbps
Encoded date                             : UTC 2015-01-07 20:14:22
Writing application                      : mkvmerge v7.4.0 ('Circles') 64bit built on Dec 17 2014 11:31:10
Writing library                          : libebml v1.3.0 + libmatroska v1.4.1


Video
ID                                       : 1
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : Baseline@L4.2
Format settings, CABAC                   : No
Format settings, ReFrames                : 1 frame
Codec ID                                 : V_MPEG4/ISO/AVC
Bit rate                                 : 266 Kbps
Width                                    : 1 280 pixels
Height                                   : 1 024 pixels
Display aspect ratio                     : 5:4
Frame rate mode                          : Variable
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Writing library                          : x264 core 138 r2363 c628e3b
Encoding settings                        : cabac=0 / ref=1 / deblock=0:1:1 / analyse=0:0 / me=dia / subme=0 / psy=1 / psy_rd=0.40:0.00 / mixed_ref=0 / me_range=16 / chroma_me=1 / trellis=0 / 8x8dct=0 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=0 / threads=12 / lookahead_threads=2 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=0 / weightp=0 / keyint=250 / keyint_min=25 / scenecut=0 / intra_refresh=0 / rc=crf / mbtree=0 / crf=22.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=0
Default                                  : Yes
Forced                                   : No


Audio
ID                                       : 2
Format                                   : DTS
Format/Info                              : Digital Theater Systems
Mode                                     : 16
Format settings, Endianness              : Big
Codec ID                                 : A_DTS
Duration                                 : 2h 35mn
Bit rate mode                            : Constant
Bit rate                                 : 1 509 Kbps
Channel(s)                               : 6 channels
Channel positions                        : Front: L C R, Side: L R, LFE
Sampling rate                            : 48.0 KHz
Bit depth                                : 24 bits
Compression mode                         : Lossy
Stream size                              : 1.64 GiB (83%)
Language                                 : English
Default                                  : Yes
Forced                                   : No

time summary

exiftool
real    0m0.089s
user    0m0.081s
sys     0m0.008s
mplayer
real    0m0.050s
user    0m0.034s
sys     0m0.017s
ffprobe/ffmpeg
real    0m0.017s
user    0m0.011s
sys     0m0.007s
mediainfo
real    0m0.029s
user    0m0.025s
sys     0m0.004s

YMMV, but ffprobe is the fastest followed by mediainfo then mplayer and finally exiftool

ffprobe < mediainfo < mplayer < exiftool

Use ffprobe:

ffprobe -v error -select_streams v:0 -show_entries stream=width,height -of csv=s=x:p=0 input.mp4

Example output:

1280x720

See FFprobe Documentation and FFmpeg Wiki: FFprobe Tips for more info.

If you are just interested in the resolution:

ffprobe -v error -of flat=s=_ -select_streams v:0 -show_entries stream=height,width video.mkv

It works also on Windows. This is running right now on my PC to build an index of all files:

find //Q1207/Film -size +10000k -print -a -exec ./ffprobe.exe -v error -of flat=s=_ -select_streams v:0 -show_entries stream=height,width \{\} \; > //Q1207/Film/index.txt

To return only the Width and Height mediainfo is an excellent tool.

mediainfo --Inform="Video;%Width%" Videofile && mediainfo --Inform="Video;%Height%" Videofile will do exactly that, no more, no less, for a vast array of supported video files.

There is a long list of useful Inform= parameters which you can obtain with the command mediainfo --Info-Parameters

If you want the output in standard WidthXHeight format use Width=$(mediainfo --Inform="Video;%Width%" Video.File)&& Height=$(mediainfo --Inform="Video;%Height%" Video.File)&&echo $Width"X"$Height

There's a bash script here that you could easily modify to meet your needs.

Or as darkdragon mentioned in a comment recently mediainfo --Inform="Video;%Width%X%Height%" Videofile

Sources:

Adding an Overlay Using FFMPEG With Minimal Re-Encoding

http://manpages.ubuntu.com/manpages/xenial/man1/mediainfo.1.html

whiptail: How to redirect output to environment variable?

How to concatenate string variables in Bash

Here's an "almost-one-liner" I've concocted around ffprobe for exactly this purpose. Works pretty well for me both on Linux and MacOS.

#!/bin/bash


B='[[:blank:]]'
D='[[:digit:]]'
ffprobe "$1" 2>&1 \
| grep 'Stream.*Video.*fps' \
| sed "s/^.*$B\($D$D$D*x$D$D$D*\).*$/\1/"

If you are not a terminal freak just open the file in Handbrake. It reports the image dimensions along with the file name. Works with mkv files.