Some FLV and MP4 video files use AAC audio tracks. Instead of converting FLV and MP4 to M4A, M4V you can demux or extract AAC from FLV, MP4 to avoid recompression (and quality loss).

Software that can demux / extract AAC tracks from FLV and MP4 files

• Replay Media Catcher 4 (Shareware/Windows) - allows to extract MP3 or AAC audio tracks and save them as MP3 or M4A/M4B audio files.
• FLV Extract (Freeware/Windows) - allows to extract audio tracks and save them as MP3, AAC, Speex, or WAV (PCM)
• Avidemux (Freeware/Windows)
• DSM Converter (from Media Player Classic) (Freeware/Windows)