[Python] Dynamically parsing API response into the correct types with msgspec

Below is a toy example I am unable to get working. How to properly configure msgspec so it will automatically select the correct types (structs)? I can't change the JSON input as it it something that I don't have any control over. I provided 2 examples how that JSON may look like: image or video

import json
import msgspec
from typing import Union

class Image(msgspec.Struct):
format: str

class Video(msgspec.Struct):
format: str

MediaType = Union[Image, Video]

class Media(msgspec.Struct):
width: int
height: int
mediaType: MediaType

DECODER = msgspec.json.Decoder(Media)

image = {"width": 100,
"height": 200,
"mediaType": {
"Image": {
"format": "jpg"
}
}
}

video = {"width": 100,
"height": 200,
"mediaType": {
"Video": {
"format": "mp4"
}
}
}


image_str = json.dumps(image)
video_str = json.dumps(video)

image_str_decoded = DECODER.decode(image_str)
video_str_decoded = DECODER.decode(video_str)

print(image_str_decoded)
print(video_str_decoded)


What I am trying to achieve:

image_str_decoded(width=100, height=200, mediaType=Image(format=jpg))
video_str_decoded(width=100, height=200, mediaType=Video(format=mp4))

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