Convert MP4 to 3G2 — Free Online Tool
Convert MP4 videos to 3G2 format, the CDMA mobile network container developed for 3GPP2 devices, using H.264 video and AAC audio encoded directly in your browser. This tool is ideal for preparing video content for legacy CDMA handsets and mobile systems that require the 3G2 container rather than standard MP4.
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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
Unlike a simple remux, converting MP4 to 3G2 requires active re-encoding even when the source MP4 already uses H.264 video and AAC audio. This is because the 3G2 container enforces its own atom structure and mobile-specific constraints that differ from MP4's box layout. FFmpeg re-encodes the video stream using libx264 with a CRF of 23 and the audio using AAC at 128k bitrate, then writes the result into a 3G2 container with the +faststart flag — which relocates the moov atom to the beginning of the file so it can begin playback before fully downloading, important for mobile streaming over CDMA networks. Note that any subtitle tracks, chapter markers, and secondary audio tracks present in the source MP4 will be dropped, as the 3G2 format does not support these features.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg program, the open-source multimedia processing engine that handles the decoding, re-encoding, and container remapping required to convert MP4 to 3G2. |
-i input.mp4
|
Specifies the source MP4 file as the input. FFmpeg reads the MP4 container and demuxes its video, audio, and any other streams for processing. |
-c:v libx264
|
Sets the video encoder to libx264, which re-encodes the video stream into H.264. This is required because the 3G2 container must be written with its own encoding pass even if the source MP4 already contained H.264 video. |
-c:a aac
|
Sets the audio encoder to AAC, the default and most compatible audio codec for the 3G2 container. AAC was specifically designed as the audio standard for 3GPP2 mobile content, making it the correct choice here. |
-crf 23
|
Controls H.264 video quality using Constant Rate Factor mode, where 23 is the libx264 default. Lower values produce higher quality and larger files; for CDMA mobile delivery, values of 28–35 are often more practical to reduce file size and streaming bandwidth. |
-b:a 128k
|
Sets the AAC audio bitrate to 128 kilobits per second, a standard quality level that provides good intelligibility for speech and acceptable fidelity for music within the bandwidth constraints typical of CDMA mobile streaming. |
-movflags +faststart
|
Rewrites the output 3G2 file to place the moov atom at the beginning of the file after encoding completes. This is critical for mobile streaming over CDMA connections, as it allows playback to begin before the entire file has been received. |
output.3g2
|
Specifies the output filename with the .3g2 extension, which signals FFmpeg to write the encoded streams into a 3G2 container formatted according to the 3GPP2 mobile multimedia specification. |
Common Use Cases
- Sending video content to legacy CDMA mobile phones (such as older Verizon or Sprint devices in the US) that only support 3G2 playback natively
- Archiving video for compatibility with older mobile multimedia messaging (MMS) systems that were designed around 3GPP2 standards
- Preparing video files for playback on embedded automotive or industrial systems built on CDMA chipsets that accept 3G2 but not MP4
- Delivering low-bitrate video clips over CDMA networks where the 3G2 container's mobile streaming optimizations reduce buffering
- Testing or validating video playback pipelines for telecom applications that specifically require the 3G2 format as part of their specification
Frequently Asked Questions
Because the conversion involves re-encoding the video through libx264 at CRF 23, there will be some generation loss compared to the original MP4 — even if the source was already H.264. CRF 23 is a widely used default that balances file size and visual quality well for most content, but if your source MP4 was encoded at a low CRF (high quality), the output 3G2 may look slightly softer. For maximum quality, you can lower the CRF value in the FFmpeg command; for smaller file sizes suited to CDMA streaming, raising it to 28 or 35 is a practical option.
The 3G2 container format, designed for constrained mobile environments under the 3GPP2 specification, does not support subtitle tracks, chapter markers, or multiple audio tracks. These data streams are silently dropped during conversion. If preserving subtitles is important, you should burn them into the video stream itself before converting, using FFmpeg's subtitles or ass video filter, which renders the subtitle text directly onto the video frames.
3GP was developed under the 3GPP standard for GSM networks (used by AT&T, T-Mobile, and most global carriers), while 3G2 was developed under 3GPP2 specifically for CDMA networks (historically used by Verizon and Sprint in the US). The two formats are structurally similar but have different codec profiles and network optimization characteristics. If your target device or system does not specifically require 3G2, 3GP may offer broader compatibility with modern mobile devices.
The video quality is controlled by the -crf flag, which accepts values from 0 (lossless/maximum quality, largest file) to 51 (lowest quality, smallest file). For 3G2 output targeting CDMA mobile devices with limited storage or bandwidth, values between 28 and 35 are often more practical than the default of 23. For example, replace '-crf 23' with '-crf 28' in the command: 'ffmpeg -i input.mp4 -c:v libx264 -c:a aac -crf 28 -b:a 96k -movflags +faststart output.3g2'. Lowering the audio bitrate from 128k to 96k simultaneously helps keep file sizes suitable for MMS or CDMA streaming.
Yes. On Linux or macOS, you can use a shell loop: 'for f in *.mp4; do ffmpeg -i "$f" -c:v libx264 -c:a aac -crf 23 -b:a 128k -movflags +faststart "${f%.mp4}.3g2"; done'. On Windows Command Prompt, use: 'for %f in (*.mp4) do ffmpeg -i "%f" -c:v libx264 -c:a aac -crf 23 -b:a 128k -movflags +faststart "%~nf.3g2"'. This browser-based tool processes one file at a time, so the desktop FFmpeg command is the recommended approach for bulk conversions.
File size differences depend on how your original MP4 was encoded. If the source MP4 used a lower CRF (higher quality, larger bitrate) than the 3G2 output's CRF 23, the 3G2 file will be smaller. If the source was already encoded at a similar or higher CRF, the 3G2 file may be roughly the same size or even slightly larger due to container overhead differences. The 3G2 container itself adds minimal overhead, so the dominant factor is always the re-encoding CRF and audio bitrate settings.
Technical Notes
The 3G2 format is structurally derived from the ISO Base Media File Format (ISOBMFF), the same lineage as MP4 and MOV, which is why libx264 and AAC — the default codecs for MP4 — are also valid in 3G2. However, 3G2 enforces a narrower codec profile set oriented toward mobile decoding capabilities, which is why codec options like libx265 (HEVC) and libvpx-vp9 available in MP4 are not supported in 3G2. The MJPEG video codec is technically listed as a supported option in 3G2 for motion-JPEG use cases, but libx264 is strongly preferred for any real video content due to far better compression efficiency. The -movflags +faststart flag is particularly meaningful here: it rewrites the file after encoding to place the moov atom (which contains all track metadata and seek tables) at the start of the file rather than the end, enabling progressive download playback over slow CDMA data connections without waiting for the full file to download. Audio is limited to a maximum bitrate of 256k in this tool's 3G2 profile, and the 320k option available for MP4 sources is not carried over to the 3G2 output. Because 3G2 does not support multiple audio tracks, only the first (or default) audio track from the MP4 source is included in the output.