How does the software convert an URL to an audio format to decode?

[julianlc6]

Hello everyone,
I am using the example "pipeline_http_select_decoder" from the ESP32 ADF repo, and I want to know how the code can convert an URL to an audio format in particular to decode. I mean, I know the URL of a radioweb and I know the audio format that it has (mp3), so I select the decoder of mp3, but what I want to know is how does the code to convert the URL to a "file" for decode.
I'd appreciate if anyone could give me any explanation.
Many thanks.