Convert MTS to 3G2 — Free Online Tool
Convert AVCHD camcorder footage (.mts) to 3G2 format for CDMA mobile network compatibility. This tool re-encodes the H.264 video and AC-3/AAC audio from your MTS transport stream into a 3GPP2-compliant container optimized for low-bitrate mobile delivery.
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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
MTS files use an MPEG-2 Transport Stream container — a broadcast-oriented wrapper designed for reliable streaming over error-prone channels, commonly produced by Sony and Panasonic camcorders. Converting to 3G2 requires a full transcode: the H.264 video is re-encoded (not simply remuxed) to fit the 3GPP2 container structure, and the audio — whether AC-3 or AAC in the source — is re-encoded to AAC at 128k to meet 3G2's codec constraints. The -movflags +faststart flag reorganizes the MP4-family metadata so the moov atom appears at the start of the file, enabling progressive playback over CDMA networks before the full file is downloaded. The transport stream's packetized structure is fully unwrapped in the process.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary. This is the same open-source engine running in your browser via WebAssembly — the command shown is identical to what you would run in a terminal on your desktop for files over 1GB. |
-i input.mts
|
Specifies the input file — an MTS file from an AVCHD camcorder, which uses an MPEG-2 Transport Stream container wrapping H.264 video and AC-3 or AAC audio. |
-c:v libx264
|
Sets the video encoder to libx264, re-encoding the camcorder's H.264 stream from the transport stream packetization into a format compatible with the 3G2 ISOBMFF container structure. |
-c:a aac
|
Encodes the audio output as AAC, which is required for 3G2 compatibility. This handles both cases where the source MTS contains AC-3 (Dolby Digital) or AAC audio, converting either to a 3G2-compliant AAC track. |
-crf 23
|
Sets the Constant Rate Factor for the libx264 encode to 23 — the default balanced setting. For AVCHD footage being downscaled to mobile delivery, this typically produces a significantly smaller file than the original MTS bitrate while maintaining acceptable visual quality. |
-b:a 128k
|
Sets the AAC audio output bitrate to 128 kilobits per second, appropriate for mono or stereo dialogue and ambient sound from a camcorder recording within the constraints of the 3G2 format's mobile delivery context. |
-movflags +faststart
|
Relocates the MP4-family moov atom to the beginning of the 3G2 file, enabling a CDMA mobile device or streaming player to begin playback before the full file is downloaded — a core requirement for 3GPP2 network delivery. |
output.3g2
|
Specifies the output filename with the .3g2 extension, which signals FFmpeg to use the 3GPP2 muxer and produce a file compatible with CDMA mobile devices and 3G2-aware media players. |
Common Use Cases
- Sending short camcorder clips to older CDMA feature phones or early smartphones that only support 3GPP2 playback
- Archiving compact, mobile-friendly versions of camcorder footage for distribution over legacy 3G CDMA networks in regions where CDMA infrastructure is still active
- Preparing MTS footage for playback in automotive or embedded systems that accept 3G2 but cannot handle MPEG-2 Transport Streams
- Reducing the file size of AVCHD clips for MMS messaging or upload to older mobile media portals with strict format requirements
- Converting camcorder source footage into 3G2 as a delivery format required by a specific broadcast or mobile carrier workflow
Frequently Asked Questions
Yes — this is a lossy-to-lossy transcode. The H.264 video from your AVCHD camcorder is fully re-encoded using the default CRF 23 setting, which produces visually good quality but is not bit-for-bit identical to the source. The 3G2 format was designed for mobile delivery at lower bitrates, so if your original MTS was recorded at high bitrate (e.g., 24 Mbps AVCHD), the output 3G2 will be noticeably smaller and somewhat lower in quality.
No. The 3G2 container does not support AC-3 (Dolby Digital), which some AVCHD camcorders use. This tool re-encodes the audio to AAC at 128k, which is the standard audio codec for 3G2 files. If your MTS source uses AAC audio, it will still be re-encoded rather than copied, to ensure compatibility with the 3G2 container's specific audio framing requirements.
The -movflags +faststart flag moves the MP4-family index (the moov atom) to the beginning of the 3G2 file. This is essential for mobile streaming over CDMA networks, where playback should begin before the entire file is received. Without it, a media player or mobile device would need to download the whole file before starting playback. For local playback only, it is technically optional, but it is considered best practice for any 3G2 intended for network delivery.
Yes. The -crf 23 flag controls video quality using Constant Rate Factor, where lower numbers mean higher quality and larger files. For a smaller 3G2 suitable for MMS or very constrained CDMA bandwidth, try -crf 35 or -crf 28. For better quality at the cost of file size, use -crf 18. Valid values for 3G2 with libx264 range from 0 to 51. You can also adjust audio bitrate by changing -b:a 128k to -b:a 64k or -b:a 96k to reduce file size further.
No. The 3G2 container does not support subtitle streams or multiple audio tracks. Only the primary video stream and a single audio track will be included in the output file. If your AVCHD source contains embedded subtitles or secondary language tracks, they will be silently dropped during conversion. If you need subtitle support, consider converting to MP4 or MKV instead.
Yes. On Linux or macOS, you can use a shell loop: for f in *.mts; do ffmpeg -i "$f" -c:v libx264 -c:a aac -crf 23 -b:a 128k -movflags +faststart "${f%.mts}.3g2"; done. On Windows Command Prompt, use: for %f in (*.mts) do ffmpeg -i "%f" -c:v libx264 -c:a aac -crf 23 -b:a 128k -movflags +faststart "%~nf.3g2". This is especially useful when processing a full camcorder memory card of MTS clips.
Technical Notes
MTS (AVCHD) files from Sony and Panasonic camcorders use an MPEG-2 Transport Stream wrapper, which includes packetized elementary streams with PAT/PMT tables — a structure optimized for broadcast reliability rather than file-based editing or mobile delivery. Converting to 3G2 strips this transport layer entirely and repackages the content into an ISO Base Media File Format (ISOBMFF) derived container, the same family as MP4 and MOV. The 3G2 format supports only libx264 and MJPEG for video, so the H.264 stream from the MTS source is re-encoded rather than copied — even though both formats technically use H.264 — because the transport stream packetization is incompatible with the 3G2 sample structure. Camcorder-specific metadata such as GPS coordinates, scene detection markers, and clip metadata embedded in the AVCHD directory structure (BDMV/CLIPINF) are not preserved in the 3G2 output. Chapter markers are not supported by either format in this conversion. The output 3G2 file will contain a single video track and a single AAC audio track, making it broadly compatible with 3GPP2-compliant devices but unsuitable for professional post-production workflows.