Free online AAC to NBS converter

What the AAC format is

AAC (Advanced Audio Coding) is a lossy audio codec used by Apple Music, iTunes, phones, streaming platforms, cameras, and media players. Files commonly use the .aac, .m4a, or .mp4 extension. Apple Music and iTunes, FFmpeg, mobile recording applications, and video editors can create AAC audio.

AAC stores encoded waveform audio, including vocals, instruments, effects, and background noise. It does not store the discrete note events that an NBS song requires.

What the NBS format is

NBS normally means Note Block Studio Song, a sequencer format used to create Minecraft note-block music. An NBS file stores timed notes, pitch, instrument assignments, layers, tempo, and song metadata rather than recorded sound.

NBS is useful when you want to edit a Minecraft note-block arrangement or load a song into Note Block Studio/Open Note Block Studio. Its advantage is editable musical structure: individual notes can be moved, retuned, muted, or assigned to different Minecraft instruments. It cannot accurately preserve vocals, reverb, timbre, or other continuous audio characteristics from an AAC recording.

How to actually convert AAC to NBS

Use a MIDI file as the intermediate format. The practical workflow is:

1. Decode the AAC file to WAV. FFmpeg avoids an additional lossy encoding step during processing:
   ffmpeg -i input.aac -ar 44100 -ac 1 working.wav
2. Transcribe the WAV to MIDI. An audio-to-MIDI application such as Melodyne or Spotify Basic Pitch can detect pitches and note timing. With Basic Pitch, a typical command is:
   basic-pitch midi-output working.wav
   The result is normally a MIDI file in the selected output directory.
3. Open the MIDI in Open Note Block Studio or Note Block Studio. Use the program's MIDI import command, then check the detected tempo, quantization, instruments, octave range, and note density.
4. Repair the arrangement manually. Delete false detections, correct missed notes, split or merge notes where necessary, and assign Minecraft instruments. Audio transcription is rarely exact, especially with drums, chords, vocals, distortion, or heavy effects.
5. Save the project as NBS. Use File → Save As and select the .nbs format if the application does not save it automatically.

You can use the free converter on 101convert.com without installing software for formats it supports, but a normal AAC-to-NBS conversion still requires musical transcription and NBS-specific editing; AAC is not a source format from which an NBS note sequence can be recovered exactly.

Quality, compatibility, and limitations

Converting AAC to WAV does not restore quality lost during AAC compression. It only gives the transcription software a broadly compatible input. Keep the original AAC file as the archival source.

Audio-to-MIDI detection works best with clean, isolated melodies and a steady tempo. Full mixes can produce incorrect notes, octave errors, excessive MIDI events, and poor timing. NBS also has a limited Minecraft pitch and instrument model, so some detected notes may need transposition or removal.

For a song already available as MIDI, import that MIDI directly instead of transcribing AAC. It will normally produce a substantially more accurate NBS arrangement.