MyMediaTools

Convert 3G2 to MP4 — Free Online Tool

Convert 3G2 files from older CDMA mobile devices into universally compatible MP4 format, re-encoding the video with H.264 and audio with AAC — the same codecs already used in 3G2, but wrapped in an MP4 container with web-optimized faststart metadata for seamless playback everywhere.

FFmpeg Command

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Estimated output:

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How It Works

3G2 and MP4 are closely related container formats — both are derived from the MPEG-4 Part 12 base specification — so the conversion is relatively lightweight. Since 3G2 files typically use H.264 video and AAC audio (the same defaults used in MP4), this tool re-encodes both streams using libx264 and AAC at standard quality settings (CRF 23 for video, 128k for audio). The re-encoding step ensures the output is clean and broadly compatible, while the -movflags +faststart flag relocates the MP4 index (moov atom) to the beginning of the file, enabling progressive playback in browsers and streaming platforms without downloading the entire file first. Because 3G2 was designed for low-bitrate CDMA transmission, source files are often highly compressed, so the output MP4 may not significantly increase in quality but will gain dramatically wider device and platform compatibility.

What Each Flag Does

Flag What it does
ffmpeg Invokes the FFmpeg program, which is running here as a WebAssembly (FFmpeg.wasm) instance entirely inside your browser — no files leave your device during this conversion.
-i input.3g2 Specifies the input file in 3G2 format, the CDMA mobile container format developed under 3GPP2 standards. FFmpeg detects the container and its H.264 video and AAC audio streams automatically.
-c:v libx264 Re-encodes the video stream using the libx264 H.264 encoder. Since 3G2 source files commonly already use H.264, this produces an output with consistent codec behavior while ensuring full compatibility with the MP4 container and all major platforms.
-c:a aac Re-encodes the audio stream using FFmpeg's built-in AAC encoder. Like the video codec, AAC is already the standard audio format in 3G2 files, so this step maintains codec parity while ensuring the audio stream is cleanly written to the MP4 container.
-crf 23 Sets the Constant Rate Factor for libx264 to 23, a widely accepted default that balances file size and visual quality. For low-resolution 3G2 source footage, this avoids adding unnecessary file size while keeping visible re-encoding artifacts minimal.
-b:a 128k Sets the audio bitrate to 128 kilobits per second, which is standard stereo AAC quality. Given that 3G2 audio was often encoded at 64k or lower for mobile network efficiency, this setting is more than sufficient to transparently represent the source audio.
-movflags +faststart Moves the MP4 moov atom (the file's structural index) to the beginning of the output file. This is essential for web streaming and platform uploads — it allows players to begin playing the video immediately without waiting for the entire file to download, unlike the default behavior where the moov atom is written at the end.
output.mp4 Specifies the output filename with the .mp4 extension, instructing FFmpeg to write the result as an MPEG-4 Part 14 container. This format is natively supported by browsers, video editors, streaming platforms, and virtually all modern playback devices.

Common Use Cases

  • Recovering old video clips shot on a CDMA flip phone or early smartphone and making them playable on modern devices like iPhones, Android phones, or smart TVs
  • Uploading archival mobile footage to YouTube, Vimeo, or Instagram, which do not accept 3G2 files but natively support H.264 MP4
  • Editing old 3G2 clips in video editors like Adobe Premiere, DaVinci Resolve, or Final Cut Pro, which have limited or no 3G2 support
  • Preserving family videos originally recorded on Verizon or Sprint CDMA phones in a future-proof container format before the original device becomes inoperable
  • Embedding mobile-era video content into a website or web application, where MP4 with faststart is the standard expected format for the HTML5 video element
  • Converting 3G2 footage received as an MMS attachment or file share so it can be incorporated into a video project alongside modern MP4 clips

Frequently Asked Questions

No — the original 3G2 file was recorded at low resolution and high compression specifically for CDMA mobile transmission, and re-encoding cannot recover detail that was never captured. The output MP4 will look essentially identical to the source, or very slightly softer due to a second encode pass. What does improve is compatibility: the same H.264 and AAC streams now live in an MP4 container that virtually every device and platform understands.
3G2 files were aggressively compressed for mobile network transmission, often at very low bitrates. When re-encoding with a general-purpose CRF 23 quality target in libx264, the encoder allocates more bits to preserve visual quality than the original encoder did, which can result in a slightly larger file. If you want a smaller output, you can raise the CRF value (e.g., -crf 28 or -crf 35) in the FFmpeg command to trade quality for smaller size.
3G2 does not support subtitle tracks or chapter markers, so there is nothing to lose in that regard during this conversion. The output MP4 container does support subtitles and chapters, but those would need to be added separately after conversion if desired.
This flag moves the MP4 moov atom (the file's index metadata) from the end of the file to the beginning. For local playback it makes no difference, but for web streaming or uploading to platforms like YouTube or social media, it allows the video to begin playing immediately as it downloads rather than requiring the full file to load first. It is strongly recommended to keep this flag for any MP4 intended for online use.
To adjust video quality, change the -crf value: lower numbers like 18 produce higher quality and larger files, while higher numbers like 28 or 35 produce smaller files with more visible compression. For audio, change -b:a to a different bitrate such as 96k for smaller files or 192k for higher fidelity. For old 3G2 source footage, values above 192k for audio or below CRF 23 for video are unlikely to produce any perceptible improvement given the quality ceiling of the original recording.
Yes — on the command line you can use a shell loop to process multiple files at once. On Linux or macOS, run: for f in *.3g2; do ffmpeg -i "$f" -c:v libx264 -c:a aac -crf 23 -b:a 128k -movflags +faststart "${f%.3g2}.mp4"; done. On Windows Command Prompt, use: for %f in (*.3g2) do ffmpeg -i "%f" -c:v libx264 -c:a aac -crf 23 -b:a 128k -movflags +faststart "%~nf.mp4". This is especially useful for digitizing a large archive of old CDMA phone videos in one pass.

Technical Notes

3G2 (3GPP2 file format) is a close sibling of MP4, both descending from the ISO Base Media File Format (MPEG-4 Part 12), which is why this conversion does not require exotic codec handling. The video codec in both the source and output defaults to H.264 (libx264), and the audio codec defaults to AAC — meaning the codec-level encoding is consistent even as the container changes. One consequence is that metadata fields specific to the 3G2 mobile context (such as 3GPP asset information or CDMA-specific track flags) will not be preserved in the MP4 output, as these are container-specific extensions with no MP4 equivalent. Because 3G2 files were designed for constrained mobile bandwidth — often targeting bitrates under 512 kbps total — the source material frequently has low resolution (176x144 to 320x240 is common) and significant blocking artifacts that become locked in permanently after the first encode. Re-encoding at CRF 23 is a reasonable general-purpose setting, but since the source quality ceiling is low, users seeking maximum fidelity from old mobile footage may benefit from experimenting with CRF 18–20 to minimize any additional generation loss, at the cost of larger file sizes.

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