Use ffprobe

Example 1: With keys / variable names

ffprobe -v error -show_entries stream=width,height -of default=noprint_wrappers=1 input.mp4
width=1280
height=720

Example 2: Just width x height

ffprobe -v error -select_streams v -show_entries stream=width,height -of csv=p=0:s=x input.m4v
1280x720

Example 3: JSON

ffprobe -v error -select_streams v -show_entries stream=width,height -of json input.mkv 
{
    "programs": [

    ],
    "streams": [
        {
            "width": 1280,
            "height": 720
        }
    ]
}

Example 4: JSON Compact

ffprobe -v error -select_streams v -show_entries stream=width,height -of json=compact=1 input.mkv 
{
    "programs": [

    ],
    "streams": [
        { "width": 1280, "height": 720 }
    ]
}

Example 5: XML

ffprobe -v error -select_streams v -show_entries stream=width,height -of xml input.mkv 
<?xml version="1.0" encoding="UTF-8"?>
<ffprobe>
    <programs>
    </programs>

    <streams>
        <stream width="1280" height="720"/>
    </streams>
</ffprobe>

---

What the options do:

• -v error Make a quiet output, but allow errors to be displayed. Excludes the usual generic FFmpeg output info including version, config, and input details.

• -show_entries stream=width,height Just show the width and height stream information.

• -of option chooses the output format (default, compact, csv, flat, ini, json, xml). See FFprobe Documentation: Writers for a description of each format and to view additional formatting options.

• -select_streams v:0 This can be added in case your input contains multiple video streams. v:0 will select only the first video stream. Otherwise you’ll get as many width and height outputs as there are video streams. -select_streams v can be used to show info from all video streams and avoid empty audio stream info in JSON and XML output.

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