Convert 3GP to M4B — Free Online Tool
Convert 3GP mobile video files to M4B audiobook format by extracting the AAC audio stream and repackaging it into an MPEG-4 container with chapter and bookmarking support. Ideal for salvaging spoken-word or lecture content recorded on older 3G mobile phones into a format natively supported by Apple Books and podcast apps.
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
3GP files are multimedia containers designed for 3G mobile devices, typically carrying H.264 or MJPEG video alongside AAC or MP3 audio. Since M4B is an audio-only MPEG-4 container, this conversion drops the video stream entirely and re-encodes (or passes through) the audio as AAC at 128k bitrate. Because both 3GP and M4B are MPEG-4-family containers and AAC is a native codec in both, the transcoding step is lightweight — the audio is decoded and re-encoded to AAC at the target bitrate rather than being losslessly copied, since the source bitrate and the target bitrate may differ. The resulting M4B file is structured with the `-movflags +faststart` optimization, which moves the MOOV metadata atom to the front of the file so that podcast and audiobook players can begin playback immediately without buffering the entire file.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary — the open-source multimedia processing engine that powers this conversion both in the browser (via FFmpeg.wasm) and on your local desktop. |
-i input.3gp
|
Specifies the input file — a 3GP container from a 3G mobile device, which may contain H.264 or MJPEG video alongside AAC or MP3 audio. FFmpeg reads all streams from this file and makes them available for mapping into the output. |
-c:a aac
|
Sets the audio codec to AAC (Advanced Audio Coding), which is the native and required codec for M4B audiobook files. Since M4B is recognized by Apple Books and podcast players specifically because of its AAC audio, this flag ensures maximum compatibility with those applications. |
-b:a 128k
|
Sets the AAC audio bitrate to 128 kilobits per second. This is the default for M4B output and represents a good balance between file size and audio clarity for spoken-word content typical of 3GP recordings such as lectures, interviews, or voice memos. |
-movflags +faststart
|
Moves the MOOV metadata atom to the beginning of the M4B file after encoding is complete. This is essential for audiobook and podcast players — including Apple Books and Apple Podcasts — because it enables immediate playback, accurate seeking, and reliable bookmarking without requiring the player to read the entire file first. |
output.m4b
|
Defines the output filename with the .m4b extension. FFmpeg uses this extension to identify the target as an MPEG-4 audiobook container, which triggers the correct MIME type and enables chapter and bookmarking atom support recognized by Apple devices and podcast applications. |
Common Use Cases
- Converting a lecture or sermon recorded as a 3GP video on an older Nokia or Samsung mobile phone into an M4B audiobook that can be loaded into Apple Books with playback position bookmarking.
- Extracting the audio from a 3GP field interview or voice memo so it can be distributed as a podcast episode in M4B format, which is natively supported by Apple Podcasts.
- Archiving spoken-word content — such as language-learning recordings or guided meditations — captured on a 3G-era phone into a durable M4B file that supports chapter markers for easy navigation.
- Stripping the low-resolution video from a 3GP recording of a radio broadcast or audiobook excerpt to produce a clean audio file compatible with audiobook players on iPhone and iPad.
- Preparing interview recordings made on a 3GP-capable device for distribution on podcast platforms that accept M4B, taking advantage of M4B's ID3 tag support for embedding title, author, and artwork metadata.
- Converting old 3GP voicemail exports or call recordings into M4B files for long-term archival with resume-playback support across Apple devices.
Frequently Asked Questions
No — M4B is a strictly audio container, so the video stream from the 3GP file is discarded during this conversion. Only the audio track is extracted and re-encoded to AAC at 128k bitrate. If preserving the video is important to you, you should convert to a video container like MP4 instead.
There is some quality loss because the audio is decoded from its original encoding and re-encoded to AAC at 128k. If the source 3GP file's audio was already at a low bitrate — common on 3G-era phones, which often used 32k–64k AAC — the output at 128k will not recover lost detail, though it won't sound worse than the source. The most audible degradation occurs when the original was already heavily compressed. For spoken-word content like lectures or audiobooks, the difference is rarely perceptible at 128k.
M4B natively supports chapters, but this conversion command does not add them automatically because 3GP files do not carry chapter metadata. To add chapters, you would need to supply a chapter metadata file separately and pass it to FFmpeg using the `-map_metadata` flag along with a chapters definition file. The tool produces a valid M4B container that is ready to accept chapters if you extend the FFmpeg command manually.
The `-movflags +faststart` flag relocates the MOOV atom — the file's index metadata — to the beginning of the M4B file. This is critical for podcast apps and audiobook players like Apple Books because it allows playback to start immediately and enables accurate resume-position bookmarking without reading the entire file first. You can technically remove it, but doing so may cause some players to display incorrect duration information or fail to seek accurately, especially with larger files.
Replace the `128k` value in the `-b:a 128k` flag with your desired bitrate. For example, use `-b:a 64k` for smaller file sizes suited to speech, or `-b:a 192k` for higher fidelity if your source 3GP audio quality justifies it. For spoken-word content typical in 3GP recordings, 64k or 96k AAC is usually indistinguishable from 128k and will produce a noticeably smaller M4B file.
Yes. On Linux or macOS, you can use a shell loop: `for f in *.3gp; do ffmpeg -i "$f" -c:a aac -b:a 128k -movflags +faststart "${f%.3gp}.m4b"; done`. On Windows Command Prompt, use: `for %f in (*.3gp) do ffmpeg -i "%f" -c:a aac -b:a 128k -movflags +faststart "%~nf.m4b"`. This is especially useful for converting a series of lecture recordings or podcast episodes stored as 3GP files.
Technical Notes
3GP is an MPEG-4-derived container standardized by 3GPP for constrained mobile environments, and its audio streams are most commonly encoded as AAC-LC or, less frequently, AMR-NB or MP3. M4B is itself an MPEG-4 Part 14 container (essentially an MP4 with a different extension and MIME type) differentiated by its support for chapter markers, bookmarking atoms, and recognition by audiobook applications. Because both formats belong to the MPEG-4 family, the container remux is efficient, but re-encoding is still required to normalize the audio bitrate to the 128k target. One notable limitation: if the source 3GP file contains AMR-NB audio (used in some very old Nokia handsets), FFmpeg will transcode it to AAC, which may produce a slightly echoey artifact at very low output bitrates — use 96k or higher in that case. Metadata such as title and artist tags present in the 3GP file may or may not map cleanly to M4B ID3-style atoms depending on how the original recording app wrote them; use `-map_metadata 0` explicitly if you need to ensure all available tags are carried over. The output file will not contain artwork or chapter markers unless these are injected separately.