Convert 3GPP to M4B — Free Online Tool
Convert 3GPP mobile video files to M4B audiobook format by stripping the video stream and re-encoding the audio track to AAC — perfect for turning mobile recordings, voice memos, or interviews captured on older phones into chapter-ready audiobook or podcast files. The M4B container adds bookmarking and chapter support that 3GPP entirely lacks.
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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
3GPP files typically contain both a video stream and an audio stream encoded in AAC or MP3, designed for low-bandwidth mobile playback on 3G networks. During this conversion, the video stream is completely discarded — M4B is an audio-only container and has no use for it. The audio stream is transcoded to AAC at 128k bitrate and placed inside the MPEG-4 audio container (.m4b). The -movflags +faststart flag rewrites the file's metadata index to the beginning of the file, which is important for streaming and progressive playback in audiobook players. Because 3GPP audio is often already AAC-encoded, you may experience minimal quality degradation, but a full re-encode does still occur rather than a lossless stream copy, since the container structures and metadata formats differ significantly. The resulting M4B file can carry chapter markers and bookmarks that allow audiobook players to remember your listening position.
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, processing your 3GPP file entirely within your browser without any server upload. |
-i input.3gp
|
Specifies the input 3GPP file. FFmpeg reads both the video and audio streams from this mobile container, though only the audio will be used in the M4B output. |
-c:a aac
|
Sets the audio codec to AAC (Advanced Audio Coding), which is the required audio format for M4B files and the standard codec used by Apple's audiobook and podcast ecosystem. This triggers a full re-encode of the 3GPP audio stream. |
-b:a 128k
|
Sets the AAC audio bitrate to 128 kilobits per second, which is the standard quality level for M4B audiobooks distributed through Apple Books — a significant step up from the typical 32–64k audio commonly found in 3GPP mobile recordings. |
-movflags +faststart
|
Moves the MP4/M4B metadata index (moov atom) to the beginning of the output file, enabling audiobook players to begin playback before the entire file is downloaded — an important behavior for streaming M4B files in podcast apps and Apple Books. |
output.m4b
|
Specifies the output filename with the .m4b extension, which signals to FFmpeg to use the MPEG-4 audio container and tells audiobook players like Apple Books, Overcast, and Pocketcasts to treat the file as a bookmarkable audiobook rather than a standard music track. |
Common Use Cases
- Converting a voice memo or interview recorded on an older Nokia or Samsung feature phone (which saved files as .3gp) into an M4B audiobook chapter for distribution on Apple Books or Overcast
- Turning a series of 3GPP lecture or sermon recordings captured on a 3G-era mobile device into a structured M4B podcast episode that supports bookmarking for listeners
- Archiving field audio recordings made on early smartphones in 3GP format into the more widely supported M4B format for long-term storage in audiobook libraries
- Extracting the audio commentary track from a 3GPP video — such as a narrated travel clip — and repackaging it as an M4B file for distribution as a guided audio tour
- Preparing mobile-captured audio content from 3GP files for import into Apple's iBooks Author or similar tools that expect M4B-formatted audiobook chapters
Frequently Asked Questions
Some quality loss is possible because the audio undergoes a full re-encode from whatever codec was used in the 3GPP file (often AAC or AMR) to AAC at 128k. If the original 3GPP file used AAC audio at a lower bitrate — which is common for mobile recordings — encoding to 128k AAC in M4B will actually match or slightly improve perceived clarity. However, if the source audio was AMR (Adaptive Multi-Rate), which is a narrowband codec optimized for voice, the wider frequency response of the AAC output may expose the original recording's bandwidth limitations.
The M4B container fully supports chapters, but this conversion tool extracts and re-encodes the audio stream only — it does not automatically generate chapter markers, since 3GPP files do not carry chapter data. Your resulting M4B file will be a valid audiobook file that can have chapters added afterward using tools like mp4chaps, Hindenburg, or Chapter and Verse. Apple Podcasts and most audiobook players will recognize the file as chapter-capable once chapter metadata is embedded.
The FFmpeg command omits an explicit -vn (no video) flag because M4B is an audio-only container format — FFmpeg automatically excludes video streams when the output container cannot carry them. No video data from the 3GPP file is written to the output, so you don't need to explicitly suppress it. If you run this command on a 3GPP file and check the output with ffprobe, you'll confirm only a single AAC audio stream is present.
Replace the value after -b:a in the command to adjust audio bitrate. For example, use -b:a 64k for a smaller file that's still acceptable for voice-only audiobook content, or -b:a 192k for higher fidelity if your 3GPP source was recorded at a high quality setting. For audiobooks and spoken word content, 64k to 96k AAC is generally indistinguishable from higher bitrates, while 128k is the standard baseline for music-quality M4B files distributed through Apple Books.
Yes — on Linux or macOS, you can run 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 PowerShell, use: Get-ChildItem *.3gp | ForEach-Object { ffmpeg -i $_.FullName -c:a aac -b:a 128k -movflags +faststart ($_.BaseName + '.m4b') }. This is especially useful if you have a collection of mobile recordings from the same device that all need to be converted for an audiobook project.
FFmpeg will attempt to copy compatible metadata tags from the 3GPP source into the M4B output, but 3GPP files often carry minimal or no metadata beyond basic duration information, especially recordings made by mobile phones rather than purchased media. The M4B container supports rich ID3-style tags including title, artist, album, album art, and description, but these will need to be added manually after conversion using a tag editor like MusicBrainz Picard, Kid3, or Apple iTunes if they weren't present in the source 3GPP file.
Technical Notes
3GPP files were engineered for constrained 3G mobile networks and typically have audio encoded at very low bitrates (as low as 4.75 kbps for AMR-NB voice) or slightly higher AAC bitrates around 32–64k for multimedia content. M4B, by contrast, is built on the MPEG-4 Part 14 container (the same foundation as MP4 and M4A) and is optimized for long-form audio with Apple ecosystem integration. One important limitation of this conversion is that AMR audio streams present in some 3GPP files must be transcoded since AAC is the only audio codec M4B supports through standard players — there is no lossless path from AMR to AAC. The -movflags +faststart flag is particularly meaningful for M4B files because audiobook players often begin playback before the full file has loaded; relocating the moov atom to the file header enables this. The output file size will vary significantly depending on the length of the original 3GPP recording: at 128k AAC, one hour of audio produces approximately 56MB, which is considerably larger than a typical 3GPP recording of equivalent duration due to the low-bitrate nature of 3GPP encoding. M4B chapter support and bookmarking are container-level features that are not populated by this FFmpeg command alone — additional tooling is required to embed chapter timestamps post-conversion.