aBookPlayer

A dark-themed Windows audiobook player with chapters, synchronized subtitles and local speech-to-text transcription, and an Android app that plays the same library on your phone.

aBookPlayer-features-1.11.mp4

Features

• Formats: MP3, M4A, M4B, AAC, MP4, WMA, WAV, FLAC, AIFF, OGG
• Books in several files: a folder of chapter files (also split into "CD 1", "CD 2"… subfolders) plays as one book, with one chapter per file
• Chapters: read from ID3 (MP3), iTunes/QuickTime and Nero chapters (M4A/M4B), Vorbis comments (FLAC/OGG); chapter list, marks on the seek bar, previous/next chapter
• Covers from the file's tags or an image in its folder, shown next to the title, in the library and in Windows' media flyout
• Library in a panel beside the subtitles (Ctrl+L shows or hides it; drag the dividers to resize the library and chapter panels, the widths are remembered): every book with its cover, author and progress, the open one highlighted; filters and search; grouped by author or by series (click a group to fold it); scans your audiobook folders; right-click a book to mark it finished, forget it, or edit its details (title, author, series, cover) when the tags are wrong
• Series: when you finish a book, the next one of its series in your library is offered
• Windows media controls: title and cover in the volume/media flyout and on the lock screen; media keys and Bluetooth headset buttons work with the window in the background; play/pause and chapter buttons in the taskbar thumbnail
• Bookmarks with notes, shown on the seek bar; export them (with the words spoken) as Markdown
• Smart rewind: after a pause, playback resumes 5–30 s earlier depending on how long it was paused
• Voice boost: evens out the narrator's volume (quiet passages louder, loud ones softer)
• Skip silences: shortens the narrator's long pauses, with position and subtitles still exact
• Sync between PCs through a shared folder (OneDrive, Dropbox, a NAS): continue on another PC where you stopped
• Your library on your phone (File → Share with your phone): the Android app lists this PC's books, plays them streaming over the home network or copies them to the phone for listening away from home, and the place in each book follows you between the phone and the PC (see Android app)
• Subtitles: .srt files kept in sync with the audio (an .srt with the same name loads automatically), adjustable delay, customizable font, color, background and position; click them to play/pause, right-click (or Ctrl+C) to copy the line on screen
• Two subtitles at once: a second .srt (a translation) shown under the first, for listening in a language you are learning (File → Load second subtitles)
• Transcription: creates a synchronized .srt (and optionally a .txt with chapter headings) using whisper.cpp via Whisper.net. Runs entirely on the PC; the model is downloaded once, on demand. Uses the graphics card through Vulkan when available (NVIDIA, AMD, Intel; GPU support is also downloaded once, on demand); with an NVIDIA card, CUDA can be chosen instead (a larger download, also on demand, of Whisper's library for it and of NVIDIA's CUDA libraries). Several books can be queued. It can also translate into English (saved as Book.en.srt and shown under the book's own subtitles)
• Audiobooks from a text: an EPUB, a PDF or a text file in English becomes an audiobook, spoken on the PC by Kokoro (the most natural voices) or Piper (lighter and much faster): one MP3 per chapter, the cover, and the text as synchronized subtitles (see Audiobooks from a text)
• Search in the subtitles (Ctrl+F) and jump to where a phrase is spoken
• Sentence by sentence: repeat the sentence just heard, go to the previous/next one, loop one (handy with a language you are learning)
• Chapters from the transcription: a book without chapters gets the headings the narrator reads ("Chapter 12", "Prologue"…)
• Audible libraries: books exported from Audible with Libation or OpenAudible are recognized by their names and tags (title, series, ASIN), play chapter by chapter, find the subtitles the export left in their folder, and sync between PCs by ASIN (aBookPlayer itself does not sign in to Audible or remove DRM: see Audible libraries)
• Playback speed 0.5×–2× without pitch change; subtitles and chapters stay in sync
• Every book remembers its position, subtitles and sync; Recent books menu
• Updates in one click: once a day (Help menu, can be turned off) it looks for a new version, shows what is new, and downloads, installs and reopens itself
• Sleep timer: after 15–90 minutes or at the end of the chapter, with a fade-out
• Skip intro and ending: seconds skipped at the start and end of a book (credits, "This is Audible"), per book or for all (Playback menu)
• Speed per book: every book keeps its own playback speed
• Mini player (Ctrl+M) always on top, and an optional icon in the notification area
• Listening statistics: time per day and per book, when you will finish the current book at your pace, a daily goal and your streak of days reaching it
• No standby while playing, and optionally no screensaver or display off (Playback → Keep screen on while playing)
• Single window ("Open with" reuses it), drag & drop, keyboard shortcuts (F1)

Audible libraries

aBookPlayer does not sign in to your Audible account and does not remove DRM. Audible has no public API for third-party apps, and its .aax/.aaxc downloads are encrypted: opening them would mean circumventing a protection measure, which the app deliberately does not do.

What it does instead is play the books you already exported to normal audio files with a tool that uses your own account, such as Libation or OpenAudible. Export once, then add the export folder to the library (Folders… at the top of the library). aBookPlayer understands what these tools write:

In the export	What aBookPlayer does
A folder per book, named Title [ASIN]	Shows the title without the long name and the ASIN code, and remembers the ASIN
One file per chapter (… - 07 - Chapter 6.mp3)	Plays them as one book, one chapter per file, named after the chapter
The whole book kept next to the chapter files (and the .mp4 it came from)	Leaves it out: the chapter files are played, the book is not played a second time
Audible tags written by AAXClean (AUDIBLE_ASIN, SERIES, PART, TIT3, narrator)	Author, series ("Dungeon Crawler Carl, Book 1") in the library, and who reads the book under the title
The subtitles the exporter left in the folder	Loaded automatically (the per-chapter ones are not, they cover only part of the book)
The ASIN	Used to recognize the same book on another PC when syncing positions, even if it sits in another folder

The library can list the books By author or By series, so a series stays together and in reading order. Transcription (Ctrl+R) works on exported files like on any other book — they are ordinary .mp3/.m4b files.

Audiobooks from a text

File → Create an audiobook from a text… (or drop an .epub, a .pdf, a .txt or an .md on the player's window, on that window itself, or on the app's icon) reads a book in English and speaks it with a neural voice, entirely on the PC.

• The book: its chapters come from the EPUB's table of contents, from the PDF's bookmarks or from the titles in the text ("Chapter 3", "PART TWO", "Prologue"…). In a PDF the running headers, the page numbers and the hyphens at the ends of the lines are removed, and the paragraphs are put back together across the pages. Covers, tables of contents, copyright pages and licenses are listed but not ticked: choose what is read. PDFs made of scanned pages (pictures, no text), pages set in two columns and EPUBs protected by DRM are not supported.
• The voice: Kokoro (one 325 MB model for all its voices: the closest to a narrator, a couple of times faster than listening on a laptop processor) or Piper (60–120 MB a voice, ten times faster than listening and more), American and British, at the speed you choose; Listen plays a sample before starting. The speech engine (about 43 MB) and the voice are downloaded once, on demand.
• Speed: several sentences are spoken at a time, on the processor or, through DirectML, on any graphics card (NVIDIA, AMD, Intel). Before a book, the app times both and uses the faster, and on the card it adds copies of the voice as long as each makes it clearly faster. A card has to get ready again for every sentence of a different length, so an integrated one is often slower than the processor. With an NVIDIA card, CUDA can be chosen instead of DirectML: NVIDIA's own libraries, usually the fastest way to run these voices on its cards. They are a 1.5 GB download (2.2 GB on the disk), made on demand from NVIDIA and nuget.org and shared in part with CUDA for the transcription, and need a recent NVIDIA driver (2025 or later).
• The result: a folder Author - Title with one MP3 per chapter (tagged; a chapter of hours is cut in parts), the cover and an .srt with every sentence at the moment it is spoken: it opens like any other book, with its chapters, cover and subtitles. A narration stopped halfway goes on from the chapter it was at.

Android app

aBookPlayer for Android (Android 6.0 and later) plays your books on the phone with the same position, bookmarks, chapters and subtitles as on the PC. It does not transcribe: the subtitles come from the Windows app.

The player leaves the screen to the subtitles: the book's cover, title and author are one small row at the top, and the subtitles' size is chosen in the player's ⋮ menu (Subtitles size); a sentence too long for it is shown smaller.

Install: the easiest way is from the PC. Open File → Share with your phone and scan the code with the phone's camera: on a phone without the app, the page it opens downloads the app from the PC (which fetches the version matching its own from GitHub). Or download aBookPlayer-<version>.apk from the latest release on the phone. Open the downloaded file to install it: Android asks once to allow installing apps from the browser or the file manager, and the browser may warn about a download from a plain HTTP address (the PC's), which is expected.

Updates: when a connected PC runs a newer version, the phone's library offers to update the app from that PC in one tap (Android asks once to allow aBookPlayer to install apps).

Play the PC's books: on the PC, turn on File → Share with your phone. On the phone, either scan the code shown there with the camera, or open Library → ⋮ → Connect to a PC, which finds the PCs on the network, and type the access key. The PC's books appear in the library ("on MYPC") and play streaming while aBookPlayer is open on the PC and the phone is on the same network; Download to this phone (in the player's ⋮ menu) copies one to listen away from home. The phone tells the PC where it stopped, and the PC tells the phone.

Or a folder on the phone: books copied to the phone (for example a folder kept in sync with the PC by Syncthing or FolderSync) can be added with Add folder; with ⋮ → Sync pointing at the same shared folder as the PCs, positions follow through it too.

The phone and the PC talk plain HTTP on the home network, each request carrying the access key; a new key (on the PC) disconnects the phones that had the old one. On Android 17 a browser asks for access to devices nearby before it can open the page of the PC's code.

Windows Firewall: phones connect to the PC on the sharing port (TCP, 52780 by default) and find it by a search on UDP port 52780. The installer, when installing for all users, adds a rule letting aBookPlayer accept connections from local network addresses only (not from the internet), unless the app already has one; uninstalling removes it. The Share with your phone window tells whether the firewall lets phones connect and find the PC, and offers Allow through Windows Firewall (it asks for administrator approval) when it may not, for example with the portable version or an installation just for the current user.

Long MP3 files (a whole book in one file, often with a variable bitrate) are served to the phone in parts of about three minutes, cut in pauses between frames: the phone then lands exactly where the PC is. The phone plays its own long MP3 files (in a folder, or copied before version 1.11.1) the same way.

Requirements

• Windows 10/11 x64
• .NET 10 SDK to build; the Android app also needs the MAUI workload (dotnet workload install maui-android)

Project layout

Folder	What it is
Core/ (aBookPlayer.Core)	Shared library, no UI and no audio decoding: tags, chapters and covers (ID3, MP4/M4B, FLAC, OGG), subtitles, Audible exports, the library's logic (scan, sorting, groups, series), per-book state, listening statistics, the sync format, and the small HTTP server and client through which a phone plays the PC's library. Used by the Android app too.
root (aBookPlayer)	The Windows app (WinForms): UI, playback with NAudio, Whisper transcription, installer and updates.
Android/ (aBookPlayer.Android)	The Android app (.NET MAUI, Android 6.0 and later): library, background playback with Media3 (notification with the position in the whole book, lock screen, headset buttons), chapters and subtitles, bookmarks, sleep timer, skipping silences, intro and ending, the next book of a series, and positions synced with the PCs through a folder kept in sync with them. It also plays the books of a PC streaming, over the home network (on the PC: File → Share with your phone), and copies them to the phone to listen away from home. No transcription: the subtitles come from the Windows app.
tests/	xUnit tests for both.

Build and run

dotnet run --project aBookPlayer.csproj

Tests

dotnet test tests/aBookPlayer.Tests

They cover subtitles, metadata/chapter/cover readers (MP3, M4B, FLAC), time stretching and sync, channel downmixing, WAV decoding, books made of several files, Audible exports (Libation/OpenAudible names, tags and subtitles), the per-book history and bookmarks, smart rewind, sync between PCs, voice boost and the library scan. GitHub Actions builds and runs them on every push to main (.github/workflows/ci.yml).

Installers

The installers are built with Inno Setup (6.3 or later):

powershell -ExecutionPolicy Bypass -File installer\build.ps1

This creates in installer\out:

File	Contents
aBookPlayer-<version>-x64-setup.exe	Self-contained, includes the .NET runtime
aBookPlayer-<version>-x64-light-setup.exe	Smaller, requires the .NET 10 Desktop Runtime
aBookPlayer-<version>-x64-portable.zip	Self-contained, no installation: unzip and run (for example from a USB stick)
aBookPlayer-<version>.apk	The Android app, signed with the app's key (built and attached apart from the workflow)

The version comes from <Version> in aBookPlayer.csproj.

Publishing a GitHub release (tag v<version>) runs .github/workflows/release.yml, which tests, builds these three files and attaches them to the release.

Data locations

• Settings: %APPDATA%\aBookPlayer\settings.json
• Whisper models: %LOCALAPPDATA%\aBookPlayer\models
• GPU support (Vulkan and CUDA builds of whisper.cpp): %LOCALAPPDATA%\aBookPlayer\gpu
• Speech engine and voices (audiobooks from a text): %LOCALAPPDATA%\aBookPlayer\speech
• NVIDIA's CUDA libraries (only if CUDA is chosen): %LOCALAPPDATA%\aBookPlayer\nvidia
• Library cover thumbnails (and covers chosen with Edit details): %LOCALAPPDATA%\aBookPlayer\covers
• Synced positions: <shared folder>\aBookPlayer sync\<PC name>.json (one file per PC)

The portable version (a portable.txt next to aBookPlayer.exe) keeps all of this in a Data folder next to it instead.

Third-party components

NAudio, NAudio.Vorbis, NVorbis, Whisper.net, whisper.cpp, QRCoder, ONNX Runtime, OnnxSharp and .NET MAUI, under the MIT License; AndroidX Media3 (the Android player) and PdfPig, under the Apache License 2.0.

Downloaded on demand, not part of the app: for the transcription on an NVIDIA card with CUDA, Whisper.net's CUDA build of whisper.cpp (MIT License) and NVIDIA's CUDA libraries (from NVIDIA, under its license); for the audiobooks from a text, the native ONNX Runtime and DirectML libraries (Microsoft, from nuget.org), NVIDIA's CUDA and cuDNN libraries (from NVIDIA, under its licenses; only if CUDA is chosen), the Kokoro-82M model (Apache License 2.0), the Piper voices (each under its own license, on its page) and eSpeak NG, which turns the text into phonemes (GNU GPL v3).

License

aBookPlayer is released under the MIT License.