File Lab
The File Lab handles document and audio file conversion. Convert between text formats, audio formats, and combine multiple audio files into a single audiobook with chapters.
Convert between supported text document formats:
| From | To | Notes |
|---|---|---|
| .txt | .pdf, .docx, .epub | |
| .txt, .docx | Text extracted via pdfplumber | |
| .docx | .txt, .pdf | |
| .epub | .txt, .docx | Chapters extracted in spine order |
Drag a file onto the drop zone, select the output format, and click Convert.
Convert between audio formats using the bundled FFmpeg:
| Format | Notes |
|---|---|
| MP3 | 192k bitrate, ID3v2 tags |
| WAV | Uncompressed, lossless |
| M4B | AAC 128k, native chapter support — ideal for audiobooks |
| MP4 | AAC 128k audio track |
| FLAC | Lossless compression |
Chapter metadata behavior by format:
| Format | Chapter Support |
|---|---|
| M4B / MP4 | Full native chapter support — chapters preserved |
| MP3 | ID3v2 chapter tags embedded |
| FLAC | Limited chapter support |
| WAV | ⚠ No chapter support — metadata lost |
The Audiobook Combiner lets you take multiple .wav files (e.g. individual chapters) and merge them into a single audiobook file with proper chapter markers.
- Drag your
.wavchapter files onto the combiner - Reorder them if needed
- Select output format (M4B recommended for audiobooks)
- Click Combine
KoKoFish calculates the duration of each file and embeds chapter timecodes automatically. The result is a single file where each original .wav becomes a named, seekable chapter.
Recommended output for audiobooks: .m4b — it has the best chapter support and is compatible with most audiobook apps (Apple Books, Plex, Jellyfin, etc.).
- Generate individual chapter audio files using the Speech Lab (one playlist item per chapter, Save as WAV), then combine them here.
- M4B is the gold standard for audiobooks if you plan to listen on a phone or audiobook player.
- WAV is best if you plan to edit the audio further in a DAW — skip chapter embedding and keep it lossless.