Audiobook Formats: M4B, MP3 & Chapter Indexing
Bookmarkable audio, spoken voice codecs, and chapter metadata.
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Format Comparison & Technical Specifications
| Output Format | MIME Type | Specification | Type |
|---|---|---|---|
| M4B Audiobook | audio/mp4 | ISO-IEC-14496-14-MP4 | MPEG-4 Chaptered Audiobook |
| MP3 Audiobook | audio/mpeg | ISO-IEC-14496-14-MP4 | Standard Spoken Audio |
| AAC Narration | audio/aac | ISO-IEC-14496-3-AAC | Advanced Audio Coding Stream |
| OPUS Speech | audio/opus | RFC-6716-OPUS | High-Efficiency Voice Stream |
Technical Specifications & Codec Breakdown
M4B vs. Standard MP3 for Spoken Audio
A standard MP3 treats an 18-hour audiobook as one long song, losing your position if paused or switched. M4B audiobooks package AAC voice compression with embedded chapter titles, cover art, and automatic bookmarking that resumes playback exactly where you left off.
Voice-Optimized Mono Bitrates
Music requires stereo channels and high bitrates (256-320 kbps). Spoken human voice recorded in mono sounds crystal clear at 64 kbps (AAC), cutting a multi-gigabyte audiobook down to a lightweight, easily downloadable file.
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