Best way to convert file from one format to another when adding to media?

[vismutx]

I can receive a file in some image image/jpeg, video/3gpp, audio/amr format from external service and saving it as

$model
->addMediaFromUrl(data_get($mediaItem, 'url'))
->toMediaCollection('attachment');

Ok, with custom ImageManipulator for video/3gpp, audio/amr I can generate preview with the help of FFMPEG

But for example audio/amr is not supported in browsers.
I would like to convert videos and audios to some general format while adding media.

Is there a way to convert files to needed audio or video on fly? Or I need to do it before adding to Media Library?

May be somebody can provide an example of solution or any ideas how to do it smart?