Convert 3G2 to M4B — Free Online Tool
Convert 3G2 video files from legacy CDMA mobile devices into M4B audiobooks or podcasts, extracting and re-encoding the audio track as AAC inside an MPEG-4 container that supports chapters and bookmarking. This tool strips the video entirely and produces a proper M4B file ready for audiobook players like Apple Books or podcast apps.
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FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
Drop your 3G2 file here
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Settings
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 is a video container built for CDMA mobile networks (used by carriers like Verizon and Sprint), typically holding H.264 video and AAC audio. M4B is an audio-only MPEG-4 container designed specifically for audiobooks and podcasts — it has no video track. During this conversion, the video stream from the 3G2 file is discarded entirely, and the AAC audio stream is decoded and re-encoded at 128k bitrate into the M4B container. Because the source audio in 3G2 is already AAC and the output is also AAC, the re-encoding step is minimal in quality impact — the main transformation is stripping the video and repackaging the audio with M4B-specific container metadata. The -movflags +faststart flag reorganizes the file's metadata index to the beginning of the file, which enables progressive playback in compatible audiobook and podcast applications.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary — in this browser-based tool, this runs as FFmpeg.wasm compiled to WebAssembly, executing entirely within your browser without sending your 3G2 file to any server. |
-i input.3g2
|
Specifies the input 3G2 file — a CDMA-era mobile video container that typically holds H.264 video and AAC audio recorded on Verizon or Sprint devices. |
-c:a aac
|
Sets the audio codec to AAC using FFmpeg's native AAC encoder, which is the required codec for M4B audiobook files and compatible with all major audiobook and podcast players including Apple Books. |
-b:a 128k
|
Sets the audio bitrate to 128 kilobits per second — a standard quality level for spoken-word M4B content that balances file size and clarity, and is typically higher than the original 3G2 mobile recording bitrate. |
-movflags +faststart
|
Relocates the MOOV metadata atom to the beginning of the M4B file so audiobook and podcast apps can begin playback and bookmarking immediately without buffering the entire file first. |
output.m4b
|
Defines the output filename with the .m4b extension, which signals to Apple Books, iTunes, and compatible podcast apps that this is an audiobook-format file with support for chapter navigation and resume-from-bookmark functionality. |
Common Use Cases
- Recovering audio from old 3G2 voice memos or recorded calls captured on CDMA-era smartphones and converting them into bookmarkable M4B files for long-term archiving
- Extracting audio commentary or narration from a 3G2 video clip recorded on an older Verizon or Sprint device and packaging it as an M4B audiobook chapter
- Converting 3G2 lecture or sermon recordings from legacy mobile devices into M4B format so listeners can resume playback from where they left off using Apple Books
- Migrating a collection of 3G2 audio recordings from an old CDMA phone into a podcast-ready M4B format compatible with modern podcast apps and directory submissions
- Stripping video from a 3G2 file to produce a lightweight M4B audio file, significantly reducing file size for storage or sharing when the visual content is irrelevant
- Preparing field recordings or interviews captured in 3G2 format on legacy devices for import into audiobook production workflows that require M4B input
Frequently Asked Questions
There is some quality loss because the audio is decoded from AAC and then re-encoded back to AAC at 128k — this is called generation loss and is inherent in any lossy-to-lossy transcode. However, 3G2 files from mobile devices were typically recorded at very low bitrates (often 64k or less) to minimize data transmission over CDMA networks, so the 128k default output bitrate may actually represent a similar or slightly higher bitrate than the original. The practical quality difference is generally negligible given the source material's constraints.
No. The 3G2 format does not support chapters, so there is no chapter data to carry over. The resulting M4B file will be a single continuous audio track with no chapter markers. If you need chapters in your M4B, you would need to add them afterward using a dedicated audiobook tool like Chapter and Verse or mp4chaps, as FFmpeg alone does not write M4B chapter metadata through this conversion workflow.
The video stream — typically H.264 encoded at low resolution for mobile screens — is completely discarded. M4B is a purely audio-oriented format and has no mechanism to store video content. Only the audio track from the 3G2 file is processed and written to the output. This is why the FFmpeg command contains no video codec flag: FFmpeg automatically drops the video when the output container cannot accommodate it.
Yes. You can change -b:a 128k to a higher value such as -b:a 192k or -b:a 256k for better quality output. However, be aware that 3G2 files recorded over CDMA networks were often encoded at very low source bitrates, so increasing the output bitrate beyond the source bitrate will increase file size without recovering audio quality that was never captured. For M4B audiobook use, 128k AAC is already considered high quality for spoken-word content.
On Linux or macOS, you can run a shell loop: for f in *.3g2; do ffmpeg -i "$f" -c:a aac -b:a 128k -movflags +faststart "${f%.3g2}.m4b"; done. On Windows Command Prompt, use: for %f in (*.3g2) do ffmpeg -i "%f" -c:a aac -b:a 128k -movflags +faststart "%~nf.m4b". This processes each 3G2 file in the current directory and produces a corresponding M4B file with the same base filename.
The M4B container extension itself signals audiobook status to Apple software, and Apple Books and iTunes will recognize it as such — enabling bookmarking and resume functionality. However, metadata like title, author, and cover art will not be populated from the 3G2 source since 3G2 files from mobile devices rarely carry rich ID3-style tags. You may want to add metadata using a tag editor like Kid3 or mp4tags after conversion for proper library organization in Apple Books.
Technical Notes
3G2 (3GPP2) was designed around the bandwidth constraints of CDMA2000 mobile networks, and its audio tracks are almost universally encoded with AAC at low bitrates — typically between 24k and 64k — using the HE-AAC profile for efficiency at low bitrates. When re-encoding these to standard AAC (LC profile) at 128k for M4B output, FFmpeg will use the native AAC encoder, which is a profile shift from HE-AAC to AAC-LC. This is technically a different codec profile, not just a repackaging, which is why full decoding and re-encoding is required rather than a simple stream copy. The -movflags +faststart flag moves the MOOV atom to the front of the file, which is essential for M4B files to support progressive loading in audiobook apps — without it, some players require the entire file to download before playback begins. M4B's chapter and bookmarking features are container-level metadata not populated by this FFmpeg command; the output is a valid M4B that supports those features but arrives without chapter markers unless added in a subsequent step. The conversion does not preserve any 3G2-specific metadata such as GPS tags or device information, which are irrelevant to the audiobook context.