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38 lines
1.8 KiB
Markdown
38 lines
1.8 KiB
Markdown
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# M4B Authoring Tool
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## Overview
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Audiobookshelf includes a built-in tool to merge multi-file audiobooks into a single M4B file. This tool is accessible via the **Manage** tab of any book.
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## "Stream Copy" (Zero Re-encode)
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The most significant improvement to the authoring tool is the **Stream Copy** (Codec: `Copy`) feature.
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### Benefits
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- **Quality Preservation**: Since the audio is not re-encoded, there is zero loss in audio quality during the merge.
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- **Speed**: Processing time is reduced from minutes (for re-encoding) to seconds (for disk I/O).
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- **CPU Efficiency**: Minimal processing power is required compared to transcoding.
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### How it Works
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1. **Concatenation**: FFmpeg uses the `concat` demuxer to join the source files into a continuous stream without decoding them.
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2. **Container Swap**: The stream is wrapped into an MP4/M4B container.
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3. **Metadata Injection**: Chapters, title, artist, and cover art are injected in a secondary pass, again using `-c copy`.
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## Feature Matrix
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| Feature | Support |
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| :--- | :--- |
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| **Codecs** | AAC, OPUS, Copy (Stream Copy) |
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| **Chapters** | Automatically generated from Library Item tracks |
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| **Cover Art** | Embedded as a video stream (attached_pic) |
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| **Metadata** | Title, Artist, Album, and Comment tags |
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## Usage
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1. Navigate to a book with multiple audio files.
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2. Go to **Manage** -> **M4B Encoder**.
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3. Select **Codec: Copy**.
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4. Click **Merge**.
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5. Once complete, a new M4B file will appear in the "Files" tab, and you will be prompted to swap the library item to the new file (optional).
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## Requirements
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- Source files must be compatible with the M4B container (typically AAC/M4A/MP3).
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- **Note**: While MP3 files can technically be copied into an M4B container, some players may have better compatibility if MP3s are transcoded to AAC.
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