Brahmavihara/four immeasurables commentary/practical actual meditation practice

Does anyone have a commentary, source, YT video of teachings or any sort of explanation of the actual method for meditations of the four immesurables (Brahmavihara) Either Mahayana or Theravada. I don't mean sutta sources, but actual explanation of the method of meditation practice. I did search the questions but could not find an adequate explanation I am seeking. Feel free to close the question and provide source if one had been provided in questions before. Though again I am looking for actual explanation of method, not just concept or translations of suttas.