Practical Common Lisp

CHAPTER 25Practical: An ID3 Parser

With a library for parsing binary data, you're ready to write some code for reading and writing an actual binary format, that of ID3 tags. ID3 tags are used to embed metadata in MP3 audio files. Dealing with ID3 tags will be a good test of the binary data library because the ID3 format is a true real-world format—a mix of engineering trade-offs and idiosyncratic design choices that does, whatever else might be said about it, get the job done. In case you missed the file-sharing revolution, here's a quick overview of what ID3 tags are and how they relate to MP3 files.

MP3, also known as MPEG Audio Layer 3, is a format for storing compressed audio data, designed by researchers at Fraunhofer IIS and standardized ...