mpeg-audio-header

Parse metadata of an MPEG audio stream from VBR (XING/VBRI) and MPEG frame headers.

Motivation

The specification of the MPEG audio format is very weak. There is no dedicated header that contains consistent metadata of the encoded audio stream like the number of channels, the sample rate (Hz), or the average bitrate (bits per second) for estimating the compression ratio and audio quality.

This library aims to determine audio metadata by applying a best effort heuristic. The metadata is either contained in a VBR header (XING/VBRI) that precedes the audio frames or it could be collected and aggregated from all MPEG frame headers to obtain more precise and reliable information.

Limitations

The metadata parser has deliberately been designed as fault tolerant and may provide results even for corrupt or invalid files. The accuracy of such results is undefined. A more restritive parsing strategy with respective error reporting might be added in the future. Currently only I/O errors could stop the parser from continuing.

This crate does not aim to parse ID3 or APE metadata and never will. Use a dedicated crate like id3 or ape for this purpose.

Testing

Test files are expected to be available in the test-data/ directory. They are not provided as part of this repository and currently need to be downloaded manually. Please refer to the .keep file in each directory which contains the respective download URL. Automatically downloading the test files on demand would be awesome.

The test files are referred to by their path. If no dedicated checks for the resulting header contents are provided then only reading the header of those files must succeed. Expected failures for corrupt files could also be verified.

Run the tests with -- --nocapture for diagnostic output on stdout/stderr.

Credits

This crate initially started as a fork of mp3-duration. Soon it became obvious that a substantial rewrite was necessary to cope with the new requirements and to properly handle all format variants corrrectly. Yet some code fragments may still reflect that heritage.

Some ideas have also been borrowed from symphonia and lofty-rs.

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or https://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in mpeg-audio-header by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.