Probably need to convert it to a lossless format first with another tool. Try reading up on VLC or ffmpeg format conversions. Extract the audio and convert it to wav. Then try to slice out the section you want with audacity. Once you have the trimmed section you can use VLC or ffmpeg to convert it to whatever audio format you want.
Do your nuts hang low? Do they wobble to and fro? Can you tie 'em in a knot? Can you tie 'em in a bow? Can you throw 'em o’er your shoulder Like a continental soldier? Do your nuts hang low?