Get a specific field from JSON using PowerShell

The ConvertFrom-Json PowerShell cmdlet can be used to achieve what you are looking for. In the code below, I’ve copy-pasted your JSON data and assigned it to the PS variable $jsonString.

Then, using the ConvertFrom-Json cmdlet, I’ve converted the JSON string into a usable PS object, $object.

I’ve given you an example at the bottom for assigning major_brand to variable $MajorBrand and then writing that out to the host.

Because of the nested structure of your provided PowerShell object, to obtain the major_brand property, we have to navigate first through parent properties tags and format. This leaves us with $object.format.tags.major_brand.

ConvertFrom-Json cmdlet info from Microsoft: https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.utility/convertfrom-json?view=powershell-7.4

# Your JSON string
$jsonString = '{
    "format": {
        "filename": ".\C0001.MP4",
        "nb_streams": 3,
        "nb_programs": 0,
        "format_name": "mov,mp4,m4a,3gp,3g2,mj2",
        "format_long_name": "QuickTime / MOV",
        "start_time": "0.000000",
        "duration": "55.680000",
        "size": "360720447",
        "bit_rate": "51827650",
        "probe_score": 100,
        "tags": {
            "major_brand": "XAVC",
            "minor_version": "16785407",
            "compatible_brands": "XAVCmp42iso2",
            "creation_time": "2023-07-28T07:10:05.000000Z"
        }
    }
}'

# Convert JSON string to PowerShell object
$object = $jsonString | ConvertFrom-Json
    
# Assign Major Brand to a variable
$MajorBrand = $($object.format.tags.major_brand)

Write-Host $MajorBrand