Convert MIDI to AAC — Free Online Converter

MIDI (.midi) is the full-extension form of the Standard MIDI File, a format that has been the backbone of electronic music communication since the MIDI 1.0 specification was published in 1983. Unlike audio recordings, .midi files encode musical intent: which notes to play, how hard to press them, which instruments to assign, and how to shape the sound with controllers like pitch bend and modulation wheel. A complex orchestral MIDI score might contain 50,000 events yet occupy only 80 KB of disk space.

AAC (Advanced Audio Coding) succeeded MP3 as the dominant perceptual audio codec, offering approximately 30% better compression efficiency at equivalent quality. Converting MIDI to AAC renders the symbolic music data into a concrete audio waveform through software synthesis, then applies AAC's psychoacoustic compression model to produce a compact, high-quality audio file. This is essential for game developers, app creators, and web developers who need to ship rendered MIDI compositions as efficient audio assets.

Game developers commonly compose music as MIDI during prototyping because it allows rapid iteration — changing instruments, tempos, and arrangements without re-recording. When the game ships, these MIDI compositions must be baked into AAC audio assets for consistent cross-platform playback. AAC's superior compression efficiency means smaller app bundles and faster download times compared to MP3.

Web developers embedding background music or interactive audio also benefit from MIDI-to-AAC conversion. The Web Audio API can play AAC natively in all major browsers, while MIDI playback in browsers requires JavaScript synthesis libraries that consume CPU and produce inconsistent results. Converting server-side to AAC offloads synthesis and guarantees identical audio for every visitor.

FFmpeg parses the .midi file header to extract the SMF format type (0 for single-track, 1 for multi-track) and the PPQN (pulses per quarter note) timing resolution — typically 480 PPQN for professional MIDI files. The decoder feeds events to a synthesis engine that maps MIDI program numbers (0-127) to General MIDI instrument patches in the loaded SoundFont. Note events trigger wavetable or sample-based oscillators with velocity-sensitive amplitude scaling. The stereo mix is encoded using AAC-LC (Low Complexity profile) via libfdk_aac or FFmpeg's native encoder, applying MDCT windowing, TNS (Temporal Noise Shaping), and Huffman coding before packaging in an ADTS or M4A container.