POST a JSON to and API

Hello Folks,

I'm trying to POST a JSON object to an API:

  "input": "",
  "output": [
      "base_url": "",
      "filename": "video.mp4",
      "thumbnails": {
        "number": 1,
        "size": "86x66"

What's the best way to post this JSON to an API, e.g.
How should I create a function that will take an input file name
( and output a JSON object as well as POST it to an API?