Why audiobook files play out of order, and how to fix the file names

Audiobook files play out of order because many players, car stereos and tools sort names character by character, like a dictionary. They see that 1 comes before 2 and put 10 - Part.mp3 ahead of 2 - Part.mp3. The fix: number the files with leading zeros so every name has the same number of digits.

Sorted letter by letter	Sorted by number
1 - Part.mp3	1 - Part.mp3
10 - Part.mp3	2 - Part.mp3
11 - Part.mp3	3 - Part.mp3
2 - Part.mp3	…
3 - Part.mp3	10 - Part.mp3
…	11 - Part.mp3

Use 01, 02 … 10 for up to 99 parts, and 001 … 100 beyond that. Then letter order and number order agree in every player and file manager.

Other things that scramble the order

• Files with no number. Prologue.mp3 usually sorts after the chapters. Number it 00 - Prologue.mp3, and give the epilogue the number after the last chapter.
• Numbers as words. Part One, Part Two, Part Three sorts as One, Three, Two. Rename them with digits.
• Mixed naming. Chapter 01.mp3 and Track 02.mp3 in one folder sort every “Chapter” before every “Track”. Use one pattern.
• Disc folders. CD1 … CD10 has the same problem one level up. Pad them (CD01), or join the discs into one book.
• Track-number tags. Some players order by the track number in the tags, not the name. A tag editor such as Mp3tag can number tracks in file-name order in one go.

Rename a whole folder at once

• macOS: select the files in Finder, right-click, Rename, and choose Format with a name and an index. Check the order first: Finder numbers them in the order they’re selected and sorted.
• Windows: PowerRename in PowerToys does batch renaming with numbering, from the right-click menu.
• Any OS: Mp3tag can rename files from their tags (for example track number and title).
• The command line: inside the book’s folder, this bash loop pads the leading number to three digits. Run it with echo in front of mv first to see what it would do.

for f in [0-9]*.mp3; do
  num=${f%%[!0-9]*}             # the leading digits
  new=$(printf '%03d%s' "$((10#$num))" "${f#"$num"}")
  [ "$f" = "$new" ] || mv -n -- "$f" "$new"
done

Change .mp3 to your extension, and %03d to %02d for two digits. mv -n never overwrites an existing file.

Or sidestep it: an M4B holds the whole book in one file, so there’s nothing to sort. M4B vs MP3 shows how to join a folder of parts into one.

How AudioSilo handles it

From server 2.4.0, AudioSilo plays a book’s files in natural order. It reads each run of digits as a number, so 2- Part plays before 10- Part and 02 counts the same as 2. That holds for a folder of files and for each disc of a book whose disc folders are joined into one. The discs themselves were already in natural order (CD2 before CD10).

AudioSilo goes by file names, not track-number tags. Natural order can’t help files with no digits: unnumbered prologues and epilogues, and numbers spelt as words.

Leading zeros are still worth adding: other players, file managers and backup tools don’t all sort naturally.

Good to know

• A book that played out of order before 2.4.0 is put right at the next library scan. Anyone partway through it may find their place has moved.
• Chapters a Bridge found for the book move with their files, so they don’t need finding again.
• A downloaded copy takes the new order the next time the book is started online in app 2.4.0. Until then, and in older apps, it plays in its download order.

The Server 2.4 release post has the rest of what changed. For the full layout, see How to organise audiobook folders and the docs’ Organizing your library, which also covers joining disc folders into one book.