Building valid JSON playlist from directory of files using MediaInfo Command Line and jq

Question

I'm using MediaInfo command line v18.08 on ubuntu to parse multiple files in a directory and output JSON, like this: mediainfo * --output=JSON

Which outputs the following JSON for each file (trimmed down a bit)

{
    "media": {
        "@ref": "openingmusic.mp3",
        "track": [
            {
                "@type": "General",
                "Duration": "17.789",
                "Encoded_Library": "LAME3.98r"
            },
            {
                "@type": "Audio",
                "Format": "MPEG Audio",
                "Encoded_Library_Settings": "-m s -V 2 -q 3 -lowpass 18.6 --vbr-old -b 32"
            }
        ]
    }
}

But I only want a subset of that JSON, so I used jq-1.5-1

mediainfo *.mp3 --output=JSON | jq '. | {duration: .media.track[0].Duration, pubDate: .media.track[0].File_Modified_Date_Local, url: .media."@ref"}'

Great, except there's no , between the elements, the whole lot isn't wrapped in [], and of course, while I can fudge that part, if I join the output, I get a trailing comma.

What's the proper jq way of doing this, please?

Answer 1

You can use the --slurp option:

• --slurp/-s:
  Instead of running the filter for each JSON object in the input, read the entire input stream into a large array and run the filter just once.

combined with a map to run your filter on each element of the array: jq -s 'map({duration: .media.track[0].Duration, pubDate: .media.track[0].File_Modified_Date_Local, url: .media."@ref"})'

Then the output will still be an array.