Compress 3G2 Online — Free File Size Reducer
Compress a 3G2 file into a smaller 3G2 file using H.264 video encoding and AAC audio, optimized for CDMA mobile network delivery. This tool re-encodes your video with tunable CRF quality settings to reduce file size while preserving the container's mobile streaming compatibility.
to
FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
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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
Because the input and output are both 3G2 containers sharing the same codec stack (H.264 video via libx264, AAC audio), this tool performs a full re-encode rather than a simple remux. The video stream is compressed using H.264 with a CRF value of 23 — a quality-based rate control method that reduces bitrate by discarding perceptually redundant visual data. The audio stream is re-encoded to AAC at 128k bitrate. The -movflags +faststart flag reorganizes the file's metadata atom to the front of the file, which is critical for 3G2 files intended for progressive download or streaming over CDMA networks, allowing playback to begin before the full file is downloaded.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary. This is the same engine running in your browser via WebAssembly (FFmpeg.wasm), so the command shown is directly portable to a local FFmpeg installation for files over 1GB. |
-i input.3g2
|
Specifies the source 3G2 file as input. FFmpeg reads the container and identifies the H.264 video and AAC (or MP3) audio streams inside the 3GPP2 wrapper before beginning re-encoding. |
-c:v libx264
|
Re-encodes the video stream using the libx264 H.264 encoder, which is the standard video codec for the 3G2 container and produces the best compression efficiency for mobile delivery. |
-crf 23
|
Sets the Constant Rate Factor for H.264 encoding to 23, the default quality level. Lower values (e.g., 18) produce larger, higher-quality files; higher values (e.g., 35) produce smaller, more compressed files — increase this number to achieve greater file size reduction. |
-c:a aac
|
Re-encodes the audio stream to AAC, the preferred audio codec for 3G2 containers. AAC delivers better audio quality than MP3 at the same low bitrates, which is important given the bandwidth constraints of CDMA mobile networks. |
-b:a 128k
|
Sets the AAC audio bitrate to 128 kilobits per second. For further file size reduction — particularly for voice or mono content common in mobile video — this can be lowered to 64k or 96k without significant perceptible quality loss. |
-movflags +faststart
|
Moves the 3G2 file's moov metadata atom to the beginning of the file after encoding completes. This is essential for 3G2 files used in mobile streaming contexts, as it allows CDMA-connected devices to begin playback before the entire file has been downloaded. |
output.3g2
|
Specifies the compressed output file in 3G2 container format. The resulting file retains full compatibility with CDMA mobile devices and 3GPP2-compliant players while occupying less storage and requiring less bandwidth to transmit. |
Common Use Cases
- Shrinking a large 3G2 video recorded on an older CDMA handset so it can be shared over MMS or a low-bandwidth mobile connection
- Reducing the storage footprint of an archive of legacy 3G2 video clips from early 2000s camera phones before long-term storage
- Re-compressing a 3G2 file that was previously exported at too high a bitrate so it fits within a mobile video portal's upload size limit
- Optimizing a 3G2 video for faster progressive streaming on a CDMA network by lowering the CRF and enabling faststart metadata placement
- Batch-preparing 3G2 training or instructional videos for distribution on embedded systems or older mobile devices with limited storage
- Lowering the bitrate of a 3G2 video file to meet the constraints of a legacy mobile application or embedded video player with strict size requirements
Frequently Asked Questions
Yes, because this process fully re-encodes the H.264 video stream rather than copying it, some generation loss is introduced. At the default CRF 23, the quality degradation is typically minor and imperceptible on small mobile screens, but if the source 3G2 was already heavily compressed (as most mobile-originated 3G2 files are), aggressively lowering the CRF or reducing audio bitrate will produce visible artifacts. For archival purposes, using CRF 18 or lower preserves more detail at the cost of a larger output file.
This can happen if the source 3G2 was encoded at a very low bitrate — for example, a video shot on a 2G-era phone at 176x144 resolution. The libx264 encoder at CRF 23 targets a quality level, not a specific file size, so if the source is already below that quality threshold, the re-encoded output may actually be larger. To guarantee a smaller file, lower the audio bitrate to 64k or 96k and increase the CRF value (try 28–35) to force more aggressive compression.
3G2 files, like MP4 and MOV files, store a metadata index called the 'moov atom' that a player needs before it can begin playback. By default, FFmpeg places this atom at the end of the file after encoding is complete. The +faststart flag moves the moov atom to the beginning, which is essential for 3G2 files streamed progressively over CDMA networks — without it, a mobile device would need to download the entire file before starting playback.
Yes — the -crf flag controls video compression, with higher values producing smaller files at lower quality. The default is 23; using -crf 28 or -crf 35 will significantly reduce file size and is often acceptable for content destined for small mobile screens. You can also reduce audio size by changing -b:a 128k to -b:a 64k, which is sufficient for speech-heavy content. The full command would look like: ffmpeg -i input.3g2 -c:v libx264 -crf 35 -c:a aac -b:a 64k -movflags +faststart output.3g2
3G2 supports limited metadata in its 'udta' (user data) atom, but FFmpeg does not guarantee preservation of all proprietary metadata tags written by mobile phone manufacturers during a re-encode. Standard tags like title and creation time may be carried over, but device-specific metadata such as GPS coordinates or camera model strings embedded by CDMA handsets are often lost. If metadata preservation is critical, inspect the source with ffprobe before and after conversion.
The command as shown processes one file at a time, but you can batch process on the command line using a shell loop. On Linux or macOS: for f in *.3g2; do ffmpeg -i "$f" -c:v libx264 -crf 23 -c:a aac -b:a 128k -movflags +faststart "compressed_$f"; done. On Windows PowerShell: Get-ChildItem *.3g2 | ForEach-Object { ffmpeg -i $_.Name -c:v libx264 -crf 23 -c:a aac -b:a 128k -movflags +faststart ("compressed_" + $_.Name) }. This is especially useful for processing large archives of legacy mobile video files.
Technical Notes
3G2 is a close relative of MP4 and MOV, sharing the ISO Base Media File Format structure, but it was specifically standardized by 3GPP2 for CDMA2000 networks (used by carriers like Verizon and Sprint in North America). The container supports H.264 (libx264) and MJPEG for video, and AAC or MP3 for audio — making it largely codec-compatible with standard MP4. However, 3G2 files in the wild are frequently encoded at very low resolutions (128x96 to 320x240) and low frame rates (10–15fps), reflecting the constraints of early CDMA handsets. When compressing 3G2 to 3G2, the libx264 encoder's CRF mode is ideal because it maintains consistent visual quality rather than hitting a fixed bitrate, which matters more on small screens than absolute bitrate numbers. One known limitation is that 3G2 does not support subtitle tracks, chapter markers, or multiple audio streams, so none of those features can be added during compression. The format also does not support transparency. AAC remains the preferred audio codec for 3G2 due to its superior efficiency at low bitrates compared to MP3, making it the right choice for the constrained bandwidth environments 3G2 was designed for.