This repository is a curated collection of links and notes on forced alignment tools, primarily aimed at researchers and developers working with speech data. It provides a comparative overview of various open-source tools, detailing their algorithms, supported languages, interfaces, and licensing, to aid in selecting the most suitable tool for tasks like creating audio-eBooks, closed captioning, and generating training data for automated speech recognition systems.

How It Works

The repository categorizes forced alignment tools based on their underlying algorithms, with many relying on Hidden Markov Models (HMM) and the HTK toolkit. Some tools, however, utilize Dynamic Time Warping (DTW) or Recurrent Neural Networks (RNN). The advantage of this curated approach lies in its practical focus, listing only tools that have been verified to install and run, while also highlighting complexities in setup and licensing considerations, particularly regarding HTK's commercial use restrictions.

Quick Start & Requirements

Installation and usage vary significantly between tools. Some offer simple CLI or library interfaces (e.g., aeneas, Kaldi), while others have more complex setups or web interfaces. Prerequisites can include specific Python versions, CUDA support (for Kaldi), and potentially large datasets or acoustic models. Links to official documentation, tutorials, and community forums are provided for many tools.

Highlighted Details

• Aeneas is noted as not being based on Automatic Speech Recognition (ASR) algorithms, differentiating it from most other tools.
• Several tools, including Kaldi and Montreal Forced Aligner, offer the ability to train for other languages beyond English.
• HTK, a common underlying toolkit, is not free for commercial purposes, necessitating a purchased license from the University of Cambridge for such use.
• CUDA support is mentioned as a feature for Kaldi.

Maintenance & Community

The project is maintained by Alberto Pettarin, with a call for community contributions to add or update information on aligners. Links to mailing lists or forums are provided for several tools, indicating active community support for individual projects.

Licensing & Compatibility

Licenses range from permissive (MIT, Apache) to copyleft (GPL, AGPL) and proprietary (MAUS - All rights reserved). The AGPL license for aeneas and GPL for FAVE-align and LaBB-CAT may have implications for closed-source commercial use due to their strong copyleft provisions. HTK's licensing also presents a potential barrier for commercial applications.

Limitations & Caveats

The README notes that the installation procedure for some tools can be "pretty complex." Additionally, the active status of some tools is marked as uncertain ("N?"). The licensing of HTK, a foundational toolkit for many listed aligners, restricts its free commercial use.