Extract Audio from 3G2 to M4B — Free Online Tool
Extract audio from 3G2 mobile video files and convert it to M4B audiobook format, preserving the AAC audio stream in an MPEG-4 container built for chapters and bookmarking. This is ideal when a 3G2 recording contains spoken content — such as a lecture or narration — that you want to use as a structured, resumable audiobook or podcast file.
to
FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
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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
3G2 files encode audio using AAC by default, and M4B is also an AAC-based MPEG-4 container — so in many cases the underlying AAC audio bitstream can be passed through with minimal re-encoding. However, this tool re-encodes the audio at 128k AAC to ensure clean compatibility with M4B's container requirements and to strip the video stream entirely using the -vn flag. The video track from the 3G2 file is discarded, and only the audio is written into the output M4B file, which is then optimized for streaming with the +faststart flag. Because 3G2 was designed for low-bitrate CDMA mobile transmission, the source audio is often already compressed at modest quality levels, so the output M4B will reflect the fidelity of the original mobile recording.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg program, the open-source multimedia processing engine that performs this conversion entirely within your browser via WebAssembly (FFmpeg.wasm). |
-i input.3g2
|
Specifies the input 3G2 file — a mobile multimedia container developed for CDMA networks, typically containing a video stream and an AAC audio stream. |
-vn
|
Disables video output entirely, discarding the video track from the 3G2 file. This is essential because M4B is a pure audio container and cannot hold a video stream. |
-c:a aac
|
Sets the audio codec to AAC (Advanced Audio Coding), which is the native and required audio format for M4B audiobook files and ensures compatibility with Apple Books and podcast applications. |
-b:a 128k
|
Sets the AAC audio bitrate to 128 kilobits per second, a standard quality level well-suited for speech content extracted from 3G2 mobile recordings, balancing file size and intelligibility. |
-movflags +faststart
|
Moves the MOOV metadata atom to the beginning of the M4B file, enabling audiobook apps and podcast players to begin streaming or playback before the entire file has loaded. |
output.m4b
|
The output filename with the .m4b extension, which signals to players like Apple Books that this MPEG-4 audio file supports audiobook features including bookmarking and chapter navigation. |
Common Use Cases
- Converting a recorded mobile lecture or conference talk stored in 3G2 format into an M4B audiobook so it can be bookmarked and resumed in Apple Books or podcast apps
- Transforming a narration or voice memo captured on an older CDMA smartphone into an M4B file for distribution as a structured podcast episode with chapter support
- Archiving spoken-word content from 3G2 video recordings — such as field notes or oral history interviews — into a portable audiobook format with proper metadata support
- Stripping the video from a 3G2 training video to create a lightweight M4B audio guide that listeners can follow hands-free on a mobile device
- Preparing a series of 3G2 mobile recordings for import into audiobook authoring tools that accept M4B as the standard input format
Frequently Asked Questions
Because 3G2 files typically carry AAC audio encoded at low bitrates optimized for CDMA mobile networks, the source quality is often the limiting factor rather than the conversion itself. The tool re-encodes to AAC at 128k, which is a clean and transparent quality level for speech content. However, since you are decoding and re-encoding lossy audio (generation loss), there will be a marginal quality reduction — for spoken word content recorded on a mobile device this is rarely perceptible.
M4B natively supports chapters, which is one of its key advantages as an audiobook format. However, this conversion tool extracts the audio track from a single 3G2 file and does not automatically generate chapter markers, since 3G2 does not carry chapter data. To add chapters to the resulting M4B, you would use a separate tool such as mp4chaps or Audiobook Builder after the conversion is complete.
The -vn flag explicitly tells FFmpeg to ignore and discard all video streams from the 3G2 input file. Without it, FFmpeg might attempt to include the video track in the output, which would fail or produce an invalid M4B file since M4B is a pure audio container with no video codec support. Using -vn ensures only the audio stream is processed and written to the output.
Replace the -b:a 128k value in the command with a higher bitrate such as -b:a 192k or -b:a 256k. For example: ffmpeg -i input.3g2 -vn -c:a aac -b:a 192k -movflags +faststart output.m4b. Keep in mind that because 3G2 audio from CDMA mobile recordings is often encoded at 64k–128k originally, increasing the output bitrate beyond the source quality will increase file size without recovering lost detail.
FFmpeg will attempt to copy compatible metadata fields — such as title and artist — from the 3G2 container into the M4B output. However, 3G2 files recorded by mobile devices often carry minimal or no metadata, so the resulting M4B may have empty tag fields. You can add or edit metadata manually after conversion using tools like MP3Tag or iTunes, both of which support M4B's ID3-compatible tagging system.
Yes, on the command line you can use a shell loop to process multiple files. On Linux or macOS: for f in *.3g2; do ffmpeg -i "$f" -vn -c:a aac -b:a 128k -movflags +faststart "${f%.3g2}.m4b"; done. On Windows PowerShell: Get-ChildItem *.3g2 | ForEach-Object { ffmpeg -i $_.Name -vn -c:a aac -b:a 128k -movflags +faststart ($_.BaseName + '.m4b') }. The browser-based tool processes one file at a time, so the local FFmpeg command is the recommended approach for batch jobs.
Technical Notes
3G2 is a variant of the MPEG-4 Part 12 container family developed for 3GPP2 and CDMA2000 networks, sharing structural DNA with MP4 and M4B. Both formats use the MPEG-4 container architecture, which means the AAC audio bitstream is technically compatible at the container level — however, re-encoding is performed here to ensure proper stream framing and M4B compliance rather than risking raw stream copy artifacts. The -movflags +faststart flag rewrites the MOOV atom to the beginning of the output file, which is important for M4B files used in streaming audiobook applications that need to begin playback before the full file is downloaded. M4B supports bookmarking at the file level, meaning compatible players like Apple Books will remember playback position — a meaningful upgrade over raw 3G2 playback. One known limitation: 3G2 does not support multiple audio tracks or subtitles, so there is no risk of accidentally including unwanted secondary streams, but it also means there is no subtitle track to carry forward. The output file size will typically be smaller than the 3G2 source when the original video track is large relative to the audio track.