Extract a soundtrack as MP3, M4A, or Opus
MP3 is lossy, and transcoding cannot restore frequencies or dynamics that were absent from the source's compressed audio. YouTube audio commonly uses Opus around 160 kb/s or AAC around 128 kb/s, though actual encodes vary. A 320 kb/s target can make a larger MP3 and may help compatibility, but it does not create 320 kb/s of original detail; constant-bitrate and variable-quality settings are distinct encoder modes. Choose native M4A or Opus when your player supports them and you prefer retaining the source encoding, or select MP3 for wider device support.
Audio-only output separates the soundtrack from the picture. A source may offer AAC in an M4A container or Opus in WebM; downloading one of those native tracks avoids changing its codec and prevents an additional lossy generation. Selecting MP3 asks FFmpeg to decode the selected audio and encode an MP3 stream for broad support in car stereos, older players, and editing software. The source format, bitrate, and estimated file size vary by video, so the same option can produce different results for different links.