Convert WebM to 3G2 — Free Online Tool
Convert WebM files (VP9 video + Opus audio) to 3G2 format using H.264 and AAC — the codec pair required for CDMA mobile network compatibility. This conversion re-encodes both the video and audio streams, making modern web-optimized content playable on legacy 3GPP2-compliant mobile devices.
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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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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
WebM uses VP9 for video and Opus for audio — neither of which is supported by the 3G2 container or legacy 3GPP2 devices. This means both streams must be fully re-encoded: the VP9 video is decoded and re-encoded to H.264 (libx264) using CRF-based quality control, and the Opus audio is decoded and re-encoded to AAC at a target bitrate. The -movflags +faststart flag reorganizes the MP4-family metadata to the front of the output file, enabling progressive playback over slow CDMA connections before the full file has downloaded. Any transparency, subtitles, chapters, or secondary audio tracks present in the source WebM will be dropped, as 3G2 does not support these features.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary — the open-source multimedia processing engine that powers this conversion in the browser via WebAssembly (FFmpeg.wasm) and can also be run directly on your desktop for files over 1GB. |
-i input.webm
|
Specifies the input file — a WebM container holding VP9 video and Opus audio, the format used natively by browsers for HTML5 video streaming and WebRTC capture. |
-c:v libx264
|
Re-encodes the VP9 video stream to H.264 using the libx264 encoder, which is required because the 3G2 container does not support VP9 and legacy 3GPP2 mobile devices only decode H.264. |
-c:a aac
|
Re-encodes the Opus audio stream to AAC using FFmpeg's built-in AAC encoder, replacing the Opus codec which is not supported in the 3G2 container format. |
-crf 23
|
Sets the H.264 Constant Rate Factor to 23, a perceptually good default quality level for the libx264 encoder. Lower values (toward 0) increase quality and file size; higher values (toward 51) reduce both, useful for CDMA bandwidth constraints. |
-b:a 128k
|
Sets the AAC audio output bitrate to 128 kilobits per second, a standard quality level that balances audio fidelity with the low-bandwidth delivery requirements typical of 3G2/CDMA use cases. |
-movflags +faststart
|
Relocates the MP4-family container metadata (moov atom) to the beginning of the 3G2 file, enabling progressive streaming playback over CDMA networks before the full file download completes. |
output.3g2
|
Defines the output filename with the .3g2 extension, signaling FFmpeg to write a 3GPP2-compliant container — the format developed for CDMA mobile multimedia transmission. |
Common Use Cases
- Preparing a VP9-encoded promotional video for playback on older CDMA-era smartphones (e.g., feature phones or early Android devices) that lack VP9 decoder support
- Distributing recorded video content through a legacy mobile content delivery system that requires 3GPP2-compliant container files
- Archiving web video content into a format compatible with older mobile multimedia messaging services (MMS) that only accept 3G2 video attachments
- Converting browser-captured WebM screen recordings into 3G2 for submission to mobile platforms or enterprise systems with strict legacy format requirements
- Downscaling a high-quality WebM video into a low-bitrate H.264/AAC 3G2 file optimized for transmission over limited-bandwidth CDMA networks
- Repackaging HTML5 web video content so it can be played on early 3G-era Qualcomm-based handsets using their built-in media players
Frequently Asked Questions
Yes — this conversion involves full re-encoding of the VP9 video stream to H.264, which is a lossy-to-lossy transcode and introduces generational quality loss. At the default CRF of 23, the output H.264 video is generally good quality for most content, but fine detail and gradients present in the original VP9 encode may degrade slightly. Opus audio is also re-encoded to AAC, which is a similarly capable lossy codec, so audio quality loss at 128k is minimal but present.
The 3G2 container format, derived from the MPEG-4 Part 12 spec for 3GPP2, was designed with the constraints of early mobile hardware and CDMA transmission in mind — it does not have standardized support for subtitle tracks or chapter markers. WebM supports both via its Matroska-derived container, but those tracks are simply not mappable to 3G2 and will be silently discarded during conversion. If subtitles are critical, consider burning them into the video stream before converting.
No. While VP9 in WebM supports an alpha channel for transparent video, the 3G2 container and H.264 codec combination used in this output does not support transparency. The alpha channel is discarded during re-encoding, and transparent areas will typically be composited against a black background in the output 3G2 file. If your WebM contains transparency that matters, you should composite it against an appropriate background color before converting.
The -crf 23 value controls H.264 video quality on a scale from 0 (lossless) to 51 (worst quality). Increasing the CRF value — for example, changing it to -crf 28 or -crf 35 — will reduce file size at the cost of lower visual quality, which is useful for CDMA transmission where bandwidth is limited. Decreasing it toward 18 will increase quality and file size. For audio, replace -b:a 128k with a lower value like -b:a 64k to further reduce the bitrate for bandwidth-constrained delivery.
The -movflags +faststart flag moves the MP4-family 'moov' metadata atom to the beginning of the file. In the 3G2 context — which targets CDMA mobile streaming — this is particularly important because it allows the device's media player to begin buffering and playing the video before the entire file has been downloaded. Without it, the metadata sits at the end of the file, forcing the player to wait for a complete download before playback can start, which is impractical over slow 3G connections.
Yes. You can use a simple shell loop to apply the same command to multiple files. On Linux or macOS, run: for f in *.webm; do ffmpeg -i "$f" -c:v libx264 -c:a aac -crf 23 -b:a 128k -movflags +faststart "${f%.webm}.3g2"; done. On Windows Command Prompt, use: for %f in (*.webm) do ffmpeg -i "%f" -c:v libx264 -c:a aac -crf 23 -b:a 128k -movflags +faststart "%~nf.3g2". The browser-based tool processes one file at a time, so the FFmpeg command is the recommended approach for bulk conversions.
Technical Notes
This conversion is a full transcode of both streams — there is no remux shortcut available because VP9 and Opus are incompatible with the 3G2 container. The libx264 encoder used here produces Baseline or Main Profile H.264, which offers the broadest compatibility with legacy 3GPP2 devices; if targeting very old hardware, you may want to explicitly add -profile:v baseline -level 3.0 to the command. The AAC encoder in FFmpeg defaults to its native AAC implementation (FFmpeg's built-in encoder), which produces compliant output suitable for 3G2. One important limitation: 3G2 supports only a single audio track, so if the source WebM contains multiple audio tracks (e.g., multiple language dubs), only the first track will be encoded. The output file size will vary significantly from the source WebM — VP9 is generally more efficient than H.264 at equivalent visual quality, meaning 3G2 files may be larger than the source at the same perceived quality, or smaller only if a higher CRF is used. The -movflags +faststart optimization is particularly meaningful for this format given its intended use in streaming over bandwidth-constrained CDMA networks.