mweralign 1.0.1
Minimum Word Error Rate Alignment for speech recognition evaluation
Requires Python: >=3.10

# mweralign

mweralign is a Python package for aligning a stream of words to a reference segmentation.
It is designed for use in speech translation tasks, where system outputs must be aligned to
a reference translation in order for standard MT metrics to work. This package is a Python
wrapper around the original MWERAlign C++ library, which implements the AS-WER algorithm for 
automatic sentence segmentation and alignment. The wrapper also includes a modernization of that
code and support for modern subword tokenization, which helps with alignment.

## Installation

To install the package, you can use pip:

    pip install mweralign

Or install from source:

    git clone https://github.com/mjpost/mweralign
    cd mweralign
    pip install .

## Usage

You can see usage information by running mweralign with the `--help` flag:

    mweralign --help

The standard use case is to provide a reference file, in which segments (sentences) are
listed one per line, and a hypothesis file, which contains the output of a speech translation system,
and has no line requirements. The output will be a file with the same number of lines as the hypothesis,
where each line contains the index of the segment in the reference that corresponds to that hypothesis
line.

    mweralign -r ref.txt -h hyp.txt -o aligned.txt

You will want to use a tokenizer. Currently supported is "cj", which segments Han characters with whitespace,
or any SentencePiece model, which are provided in the form of a filesystem path:

    mweralign -r ref.zh.txt -h hyp.txt -o aligned.txt -t cj

    # download the flores200 SPM model (one time)
    sacrebleu -t wmt24 -l en-zh --echo src | sacrebleu -t wmt24 -l en-zh --tok flores200 > /dev/null
    # align
    mweralign -r ref.txt -h hyp.txt -o aligned.txt -t ~/.sacrebleu/models/flores200sacrebleuspm

You may also wish to supply the ISO 639-1 language code (-l zh). For zh and ja, this tells the underlying
AS-WER algorithm not to prevent sentences from starting with the SentencePiece space character. For other
languages, it has no effect.

    mweralign -r ref.txt -h hyp.txt -o aligned.txt -t cj -l zh

## Citation

If you use this package, please cite the following two papers. We suggest a sentence
similar to the following: "To align the text, we used the mweralign package \citep{post-huang-2025-effects},
which implements a variant of the AS-WER algorithm \citep{matusov-etal-2005-evaluating}.

> @inproceedings{matusov2005evaluating,
>   title={Evaluating machine translation output with automatic sentence segmentation},
>   author={Matusov, Evgeny and Leusch, Gregor and Bender, Oliver and Ney, Hermann},
>   booktitle={IWSLT 2005},
>   pages={138--144},
>   year={2005}
> }

> @inproceedings{post-huang-2025-effects,
>   title={Effects of automatic alignment on speech translation metric},
>   author={Post, Matt and Hoang, Hieu},
>   booktitle={Proceedings of IWSLT 2025},
>   year={2025}
> }


## License

This project contains code under multiple licenses:

- **Original C++ alignment code**: GNU General Public License v3 (GPL-3.0)
- **Python bindings and wrapper code**: Apache License 2.0
- **Build scripts and documentation**: Apache License 2.0

**The project as a whole is distributed under GPL-3.0** due to the inclusion of GPL-licensed components.

### What this means for users:
- You can use this library in GPL-compatible projects
- If you distribute software that includes this library, your software must be GPL-compatible
- The Python wrapper code (separate from the C++ core) is available under Apache License 2.0

## Attribution
This software includes original GPL-licensed C++ code for alignment algorithms.
Python bindings and packaging by Matt Post (Apache License 2.0).