It does. M4Aは、iTunesやApple MusicのファイルのデフォルトであるAACまたはALACオーディオを保持するMP4コンテナです。. That decides whether a gain change is an exact edit of the samples or has to go through a re-encode.
透明度の決定は，透明度の変更を行う段階である。 That is the step most people actually came for, and doing it after M4A のボリュームを調整 rather than before it means the conversion works from the file you finally settled on.
