Extract Audio from AVI to M4B — Free Online Tool
Extract audio from AVI video files and save it as M4B, the MPEG-4 audiobook format with chapter and bookmarking support. The video stream is discarded and the audio is transcoded to AAC inside an M4B container — ideal for converting recorded lectures, presentations, or long-form AVI content into a format compatible with Apple Books, podcast apps, and audiobook players.
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FFmpeg Command
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Note: Browser-based encoding uses approximate quality targets. For precise CRF compression, copy the FFmpeg command above and run it on your desktop.
Estimated output:
Conversion Complete!
DownloadHow It Works
AVI files store interleaved audio and video streams, often with MP3 (libmp3lame) or AAC audio alongside H.264 video. This tool strips the video entirely and transcodes the audio stream to AAC at 128k bitrate, then wraps it in an MPEG-4 container with the .m4b extension. The -movflags +faststart flag reorganizes the file's metadata index to the beginning of the file, which enables progressive playback and streaming in audiobook apps. Because AVI does not natively support chapters, any chapter structure in the output must be added separately — but the M4B container is fully ready to accept chapter metadata if you add it via a tool like mp4chaps or ffmpeg metadata files after conversion.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg command-line tool. In the browser version of this tool, FFmpeg runs locally via WebAssembly (FFmpeg.wasm) — no files leave your machine. |
-i input.avi
|
Specifies the input AVI file. FFmpeg reads the interleaved audio and video streams from the AVI container, which may contain H.264 video and MP3 or AAC audio depending on how the file was originally created. |
-vn
|
Disables video output entirely, discarding the video stream from the AVI file. Since M4B is an audio-only format, this ensures no video data is passed through or accidentally included in the output. |
-c:a aac
|
Encodes the audio stream using the AAC codec, which is the native and required audio format for M4B files. If the source AVI contains MP3 audio (the AVI default), this performs a full transcode from MP3 to AAC. |
-b:a 128k
|
Sets the AAC audio bitrate to 128 kilobits per second, which is the standard quality level for spoken-word audiobook and podcast content. This balances file size and audio clarity well for voice recordings extracted from AVI files. |
-movflags +faststart
|
Moves the MPEG-4 moov atom (metadata index) to the beginning of the M4B file after encoding completes. This is essential for audiobook and podcast apps that need to begin playback or display chapter information before the entire file is loaded. |
output.m4b
|
The output filename with the .m4b extension, which identifies the file to Apple Books, iOS, and podcast applications as an audiobook rather than generic audio, enabling bookmarking and resume-playback features. |
Common Use Cases
- Convert a recorded university lecture stored as an AVI file into an M4B audiobook so students can listen with bookmarking and resume playback in Apple Books or Pocket Casts
- Strip the audio from an old AVI-format conference talk or keynote recording to create a listenable M4B file compatible with iOS audiobook apps
- Extract narration audio from an AVI screencast or tutorial video and package it as M4B for distribution as a podcast or audio course module
- Digitize old AVI recordings of spoken-word performances or radio plays into the audiobook-friendly M4B format for long-term archival and playback on modern devices
- Convert AVI video recordings of language learning lessons into M4B files so learners can use bookmarking to mark difficult sections and resume exactly where they left off
- Prepare a long AVI-format documentary or interview recording for audiobook distribution by extracting and re-encoding its audio track into M4B with faststart enabled for streaming
Frequently Asked Questions
It depends on what audio codec the source AVI uses. If the AVI contains AAC audio, transcoding to AAC again at 128k will introduce a small generation of quality loss since you are decoding and re-encoding a lossy format. If the AVI contains MP3 audio (which is common, as libmp3lame is AVI's default audio codec), the audio is decoded and re-encoded to AAC — again a lossy-to-lossy transcode. At 128k AAC, speech and narration content sounds excellent, but if the source audio quality is already low, the output cannot recover lost detail. For music or high-fidelity content, consider increasing the bitrate to 192k or 256k.
M4B is specifically designed for chapter support and is one of its defining advantages over generic audio formats like MP3. However, AVI does not support chapters natively, so there are no chapter timestamps to extract from the source file. This conversion produces a valid, chapter-ready M4B container, but chapter markers will not be present unless you add them afterward using a tool like mp4chaps or by embedding an FFmpeg chapter metadata file during a second pass.
Both .m4a and .m4b are MPEG-4 audio containers using AAC encoding, and they are technically almost identical at the codec level. The .m4b extension signals to audiobook and podcast applications — particularly Apple Books, iTunes, and iOS — that the file should be treated as an audiobook, enabling features like bookmarking, resume playback, and chapter navigation. A .m4a file with the same audio content would play fine but would typically be treated as regular music rather than an audiobook by these apps.
The -movflags +faststart flag moves the moov atom (the file's index and metadata block) from the end of the file to the beginning. In a standard MPEG-4 file, the moov atom is written last because the encoder doesn't know the final size until encoding is complete. By relocating it to the front, the file can begin playing or streaming before it is fully downloaded — which is critical for podcast apps and audiobook platforms that stream M4B files over the network rather than requiring a full download first.
Replace the -b:a 128k value with your desired bitrate. For example, use -b:a 192k for better quality on music or high-fidelity speech, or -b:a 96k to reduce file size for voice-only content where bandwidth is limited. The full modified command would look like: ffmpeg -i input.avi -vn -c:a aac -b:a 192k -movflags +faststart output.m4b. AAC at 128k is generally considered transparent for speech, so increases beyond 192k rarely produce audible improvement for audiobook content.
Yes. On Linux or macOS, you can loop over all AVI files in a directory with: for f in *.avi; do ffmpeg -i "$f" -vn -c:a aac -b:a 128k -movflags +faststart "${f%.avi}.m4b"; done. On Windows Command Prompt, use: for %f in (*.avi) do ffmpeg -i "%f" -vn -c:a aac -b:a 128k -movflags +faststart "%~nf.m4b". The browser-based tool processes one file at a time, so the FFmpeg command is the recommended approach for bulk conversions — particularly for large collections or files exceeding the 1GB browser limit.
Technical Notes
AVI is a legacy container that stores audio and video in an interleaved structure, which means the audio stream must be demuxed before the video can be dropped. The -vn flag handles this by telling FFmpeg to ignore all video streams entirely, avoiding unnecessary decoding work. AVI supports multiple audio tracks (unlike M4B, which is limited to a single audio stream), so if the source AVI contains multiple audio tracks, FFmpeg will default to the first one (stream 0:a:0). To select a specific track, add -map 0:a:1 (for the second track) to the command before the output filename. M4B's AAC audio codec is natively supported on all Apple devices and most Android audiobook apps, but some older Windows media players may not recognize the .m4b extension — renaming to .m4a typically resolves playback issues on those platforms without any re-encoding. ID3-style metadata (title, artist, album) embedded in the AVI file may not transfer cleanly to the M4B output, so you may need to re-tag the output file using a tool like mp4tags or a metadata editor like MP3Tag.