APC File

What are APC files and how to open them

Are you having problems opening an APC file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your APC files.

What is an APC file?

APC files have multiple uses, and A-Pac Compressed Audio is one of them. Read more about the other uses further down the page.

A-Pac Compressed Audio

A-Pac Compressed Audio is a lossless audio codec developed by Marian that stores audio without discarding any original data. It is used to compress audio using small predictive blocks so that the resulting file can be decoded back into its exact original form without quality loss. This codec was created in the 1990s and does not use perceptual techniques; instead it relies on prediction and fixed-size bit fields to encode small blocks of samples efficiently.

Marian's encoder takes an input audio file - commonly a standard PCM WAV file - and wraps its headers and metadata inside "chunks" that describe the original format (number of channels, sample rate, bits per sample, etc.), then compresses the raw audio data in blocks of a few samples (typically 8) each. This makes the format suitable for archival or storage where exact fidelity is required. A decoder reverses this process, restoring the original waveform by applying the same prediction and bit-length rules.

Files in this format begin with the ASCII signature "APAC" followed by a "PROF NAD " chunk (which holds the original file's headers such as "RIFF WAVEfmt" up to its "data" section). After that comes a "PFRT" chunk giving compression parameters like channel count, sample rate, source format code (TwoCC), bits per sample, and possibly a CRC. Then a zero-terminated original filename may appear before the actual compressed audio data inside a "PAD " chunk.

How to open APC files

Important: Different programs may use files with the APC file extension for different purposes, so unless you are sure which format your APC file is, you may need to try a few different programs.

While we have not verified the apps ourselves yet, our users have suggested ten different APC openers which you will find listed below.

Last updated: August 18, 2026

All known file formats using extension .APC

While A-Pac Compressed Audio is a popular type of APC-file, we know of 5 different uses of the .APC file extension. Different software may use files with the same extension for different types of data.

A-Pac Lossless Compressed Audio

A-Pac Lossless Compressed Audio files store audio data compressed in a lossless way, so the exact original audio can be recovered without any loss in quality. These files were produced using Marian's a-Pac audio codec, which is designed for small-block prediction and bit-field coding.

Marian's a-Pac codec packs audio data into very small blocks (typically 8 samples), predicts each sample using prior samples, and encodes the second derivative of the prediction (how the prediction error itself changes) using fixed-size bit fields. The bit-field size may adjust between blocks. The codec supports typical audio parameters such as two channels or more, various sampling rates, and bit depths (often 8-bit or 16-bit) for lossless audio. Decoding is supported in tools like FFmpeg under the name "apac" (Marian's A-pac audio).

Byte signatures used by these files include an ASCII header "APAC" at offset 0, "PROFNAD" at offset 8, "RIFF" file structure around offset 20, and "WAVEfmt" around offset 28. The format also contains a chunk labeled "PFRT" (packed audio format chunk) and another chunk "PAD " which holds the packed audio data. One of the internal keywords present is "PFMT".

Allways Printer Data File

We know that one APC format is Allways Printer Data File. We have not yet analyzed in detail what these files contain and what they are used for. We're working on it.

Cryo Interactive APC Audio

The APC file is an audio file format used in games created by Cryo Interactive Entertainment. The audio file often comes in a compressed form. It can be mono or stereo and supports different sample rates. A sample rate is the measurement of the number of audio samples per second and is measured using hertz or kilohertz.

APC files can be converted into other traditional audio file formats which can be played by a majority of audio players.

APC opener for Windows

We have identified one APC opener that is compatible with this specific type of APC file.

Oracle Audio Percussion

Oracle Audio Percussion is a music tracker format produced by the program Oracle, made by Fuzzy Logic in 1997 for the MSX computer line. It stores song data for tracker-style composition using the MSX-AUDIO, MSX-MUSIC, and PSG (programmable sound generator) hardware, allowing up to 32 channels, pattern-based sequencing, and a variety of effects such as arpeggio, tremolo, vibrato, wah-wah, volume slides and block-based repetition.

Files of this format are written by Oracle when saving a composition. Oracle is primarily used as a music editor on MSX systems; these files represent the song as it will be played by its built-in replayer. Typical workflow: the user composes a song in Oracle, which writes the song's data (patterns, steps, instruments, effects), then the MSX (with appropriate sound hardware) can load and play the file.

Oracle song files begin with a specific byte signature: the ASCII string ORACLE followed by bytes 00 01 0B at offset 0.

Various apps that use files with this extension

These apps are known to open certain types of APC files. Remember, different programs may use APC files for different purposes, so you may need to try out a few of them to be able to open your specific file.

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