Multimedia_AAC_Project/Readme.md

AAC Encoder/Decoder Assignment (Multimedia)

About

This repository contains a staged implementation of a simplified AAC-like audio coder/decoder pipeline, developed in the context of the Multimedia course at Aristotle University of Thessaloniki (AUTh). The project is organized into incremental levels, where each level introduces additional functionality and requirements (e.g., segmentation control, filterbanks, and progressively more complete encoding/decoding stages). The purpose of this work is to implement the specified processing chain faithfully to the assignment specification, validate correctness with structured tests, and maintain a clean, reproducible project structure throughout development.

Repository Structure

The repository is organized under the source/ directory and split into three incremental levels:

• source/level_1/
  Baseline implementation of the required processing chain for Level 1.

• source/level_2/
  Placeholder for Level 2 implementation (to be filled step-by-step).

• source/level_3/
  Placeholder for Level 3 implementation (to be filled step-by-step).

Each level contains:

• a module file (e.g., level_1/level_1.py)
• a dedicated tests/ directory for module-level tests (pytest)

Level Descriptions

Level 1

Goal: Implement the core analysis/synthesis chain for Level 1 as defined in the assignment specification.

Implemented components (current status):

• SSC (Sequence Segmentation Control)
• Filterbank (MDCT analysis) and inverse filterbank (IMDCT synthesis)
• End-to-end encoder/decoder functions:
  • aac_coder_1()
  • i_aac_coder_1()
• Demo function:
  • demo_aac_1()

Tests (current status):

• Module-level tests for SSC
• Module-level tests for filterbank and inverse filterbank (including OLA-based reconstruction checks)
• Internal consistency tests for MDCT/IMDCT
• Module-level tests for aac_coder_1 / i_aac_coder_1

Level 2

Goal: ...

Level 3

Goal: ...

How to Run

All commands below assume you are inside the source/ directory.

Run Level 1 Demo

Run the Level 1 demo by providing an input WAV file and an output WAV file:

python -m level_1.level_1 <input.wav> <output.wav>

Example:

python -m level_1.level_1 ../material/LicorDeCalandraca.wav ../material/LicorDeCalandraca_out.wav

The demo prints the overall SNR (in dB) between the original and reconstructed audio.

How to Run Tests

Tests are written using pytest and are organized per level.

From inside source/, run all tests:

pytest

To run only level_1/tests

pytest level_1/tests

To run a specific test file:

pytest level_1/tests/test_SSC.py

Notes on Development Workflow

• The project is developed incrementally, level-by-level.
• Tests are primarily module-level and specification-driven.
• Internal helper testing is avoided in general, except for MDCT/IMDCT which are treated as reusable “library-like” primitives.

Disclaimer

This project was developed solely for educational purposes. It is provided "as is", without any express or implied warranties. The author assumes no responsibility for any misuse, data loss, security incidents, or damages resulting from the use of this software. This implementation should not be used in production environments.

All work, modifications, and results are the sole responsibility of the author.