feat(converter): add per-chapter and m4b output

1 files changed, 28 insertions, 2 deletions

diff --git a/README.md b/README.md
index 44422b9..17568eb 100644
--- a/README.md
+++ b/README.md
@@ -10,7 +10,7 @@ Original project: [https://github.com/WhiskeyCoder/Qwen3-Audiobook-Converter](ht
 The converter sends text extracted from your books to a locally running Qwen3-TTS server and assembles the returned audio into a single audiobook file.
 
 - Supported input: `.txt`, `.pdf`, `.epub`
-- Output: `.mp3`
+- Output: `.mp3` or `.m4b`
 - Two voice modes:
   - Custom voice: pre-built speakers
   - Voice clone: clone a voice from a `.wav` reference audio file
@@ -67,7 +67,7 @@ qwen-tts-demo Qwen/Qwen3-TTS-12Hz-1.7B-Base --ip 127.0.0.1 --port 7861
 
 ## Converting books
 
-Put your book files (epub, txt, etc.) in the `book_to_convert/` folder. Then run the script. The output mp3 goes to `audiobooks/`.
+Put your book files (epub, txt, etc.) in the `input/` folder. Then run the script. The output goes to `output/`.
 
 ### Custom voice
 
@@ -105,6 +105,32 @@ Adjust the speed of the final audiobook without changing pitch (uses ffmpeg `ate
 python audiobook_converter.py --speed 0.9
 ```
 
+### Output format (mp3 / m4b)
+
+Use `--format` to choose the output container. The default is `mp3`; `m4b` uses AAC audio (ffmpeg `aac`).
+
+```bash
+python audiobook_converter.py --format m4b
+```
+
+### Chapters (EPUB)
+
+Books with chapters (e.g. EPUB) are converted to **one file per chapter** by default. Files are named `output/<Book>_01_<Chapter>.mp3`, `output/<Book>_02_<Chapter>.mp3`, and so on.
+
+To merge all chapters into a single file instead, pass `--single-file`:
+
+```bash
+python audiobook_converter.py --single-file
+```
+
+When the source has chapters and the output is a single `m4b`, chapter markers are embedded so listeners can skip between chapters:
+
+```bash
+python audiobook_converter.py --format m4b --single-file
+```
+
+TXT and PDF files have no chapter structure and always produce a single file.
+
 The `chunks/` folder is scratch space for the current book only — it is emptied before and after every conversion, so an interrupted run never affects the next one.
 
 ## Running tests