How to extract audio from a video
Choosing a format and a bitrate that suit what you are actually keeping.
Copy it if you can
Most videos carry AAC audio. Extracting to M4A keeps that stream exactly as it is — instant, and with no quality loss at all. Converting the same audio to MP3 means decoding and re-encoding it, which always costs something.
Match the bitrate to the content
Speech is simple to encode: 128 kbps is transparent for a lecture or a podcast and produces a file you can actually store on a phone. Music benefits from 192 kbps or more. Above 256 kbps you are almost certainly storing data you will never hear.