Concatenating MP3 Files

Apple requires that you deliver your audiobook as a single, large file, with metadata (in the form of an xml input file) designating the start of each chapter. The audio file is delivered in a <track> tag, with the file being less than 23 hours in length. (For longer audiobooks, you can deliver multiple tracks, and each track can be up to 23 hours long. If a single track audio file is longer than 23 hours, delivery will fail.) The goal is to send the audio in as few tracks as possible, with each track as close to the 23 hour limit as possible.

If your audiobook is currently broken up into multiple MP3 files of short duration, you must concatenate them into a single, longer track (or multiple long tracks, if the combined duration is longer than 23 hours). The required solution for concatenating MP3 files into a single, longer file is provided below.

When concatenating files, you must track the precise cumulative duration of the files. You may choose to round to the nearest second in specifying the chapter marks (see the annotation for Audiobook Track Chaptering in Basic Audiobook Metadata Annotated), but you should use sub-second precision in tracking the cumulative length of the concatenated files; otherwise, your chapter points will gradually become more inaccurate further into the track as the imprecision is compounded.