Convert M2TS to 3G2 — Free Online Tool
Convert M2TS Blu-ray and AVCHD video files to 3G2 format for CDMA mobile devices, re-encoding the H.264 video stream and AAC audio into a compact, mobile-optimized container with fast-start streaming support. This tool dramatically reduces file size by targeting mobile bitrates while preserving the core video content from your high-definition source.
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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
M2TS files use an MPEG-2 Transport Stream wrapper — the same container architecture used in Blu-ray discs and AVCHD camcorders — which typically carries H.264 or H.265 video alongside multi-channel audio like AC-3 or DTS. The 3G2 container, built for 3GPP2 CDMA networks, has a much narrower codec profile: it supports only H.264 video and AAC or MP3 audio. This conversion fully re-encodes the video using libx264 at CRF 23 (a visually balanced quality level) and transcodes any audio track — including AC-3, DTS, or multi-channel AAC from the M2TS source — down to stereo AAC at 128k. Subtitles and additional audio tracks present in the M2TS cannot be carried into 3G2, so only the primary video and first audio track are preserved. The -movflags +faststart flag reorganizes the output file's metadata to the front, enabling progressive playback on mobile connections before the full file has downloaded.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg program, the open-source multimedia processing engine that handles the actual decoding of the M2TS transport stream and encoding into the 3G2 container. |
-i input.m2ts
|
Specifies the input M2TS file — a Blu-ray or AVCHD transport stream that may contain HD video, multi-channel audio (AC-3, DTS, or AAC), and subtitle tracks. |
-c:v libx264
|
Re-encodes the video stream using the libx264 H.264 encoder, which is the standard video codec for 3G2 and provides broad compatibility with mobile devices and players. |
-c:a aac
|
Transcodes the audio from whatever codec the M2TS source uses — often AC-3 or DTS — into AAC stereo, the standard audio format supported by the 3G2 container. |
-crf 23
|
Sets the Constant Rate Factor for the H.264 encode to 23, a balanced default that trades minor quality reduction against significant file size savings compared to the high-bitrate M2TS source. |
-b:a 128k
|
Sets the AAC audio output bitrate to 128 kilobits per second, an appropriate quality level for stereo mobile audio that keeps the 3G2 file size compact for CDMA network transmission. |
-movflags +faststart
|
Relocates the 3G2 file's moov metadata atom to the beginning of the file, enabling progressive playback to start over a mobile connection before the entire file is downloaded — a critical feature for the low-bandwidth CDMA networks 3G2 was designed for. |
output.3g2
|
Specifies the output filename with the .3g2 extension, which tells FFmpeg to mux the encoded H.264 video and AAC audio into the 3GPP2 mobile container format. |
Common Use Cases
- Archiving a specific scene or clip from a Blu-ray rip for playback on an older CDMA smartphone or feature phone that only supports 3G2 media
- Trimming down a large AVCHD camcorder recording from an M2TS file into a compact 3G2 clip to share over a CDMA mobile network with strict file-size limits
- Converting Blu-ray concert or event footage to 3G2 for playback in legacy media player applications on early Android or BREW-based devices
- Preparing a short video clip from an M2TS broadcast capture for embedding in a CDMA-era mobile multimedia message (MMS) where 3G2 was the required format
- Downscaling a high-definition AVCHD home video to a mobile-compatible 3G2 file for storage on a device with very limited internal memory
- Testing cross-format playback compatibility between broadcast-grade M2TS sources and mobile 3G2 players as part of a legacy media digitization workflow
Frequently Asked Questions
Yes, some quality loss is unavoidable because 3G2 is a lossy-only format designed for mobile bandwidth constraints, while M2TS files typically contain high-definition video at high bitrates. The default CRF 23 setting used here produces visually acceptable quality for smaller screens, but the resulting file will be significantly lower bitrate than the original Blu-ray or AVCHD source. If your source M2TS carries H.265 or high-bitrate H.264, re-encoding to H.264 inside 3G2 at CRF 23 will be noticeably softer when viewed on a large display.
AC-3 (Dolby Digital) and DTS audio tracks — both common in Blu-ray M2TS files — cannot be stored in a 3G2 container. This tool transcodes the first audio track from whatever codec the M2TS uses into stereo AAC at 128k, which is the standard audio format for 3G2. Multi-channel surround sound is downmixed to two channels in the process. If your M2TS has multiple audio tracks (e.g., commentary tracks or alternate languages), only the primary track will be included in the output.
No. The 3G2 container does not support subtitle streams, so any PGS (Blu-ray bitmap subtitles) or text-based subtitle tracks present in the M2TS source are dropped during conversion. If subtitles are important, you would need to burn them directly into the video using a libass or overlay filter before this conversion, which requires modifying the FFmpeg command beyond the default shown here.
The -movflags +faststart flag moves the MP4/3G2 moov atom (the file's index metadata) from the end of the file to the beginning. Without this, a media player or mobile browser must download the entire 3G2 file before it can begin playback. With faststart, playback can begin as soon as the initial metadata is received over a CDMA connection, which was especially important for the low-bandwidth mobile networks 3G2 was designed for.
Adjust the -crf value in the command — lower numbers mean higher quality and larger file sizes, while higher numbers compress more aggressively with more quality loss. For example, changing -crf 23 to -crf 18 produces near-transparent quality relative to the source but increases file size considerably, while -crf 28 or -crf 35 produces smaller files better suited to mobile storage limits. For 3G2 files destined for mobile playback on small screens, a CRF between 25 and 35 is usually a practical range since fine detail is hard to perceive on small displays.
Yes. On Linux or macOS, you can run a shell loop: for f in *.m2ts; do ffmpeg -i "$f" -c:v libx264 -c:a aac -crf 23 -b:a 128k -movflags +faststart "${f%.m2ts}.3g2"; done. On Windows Command Prompt, use: for %f in (*.m2ts) do ffmpeg -i "%f" -c:v libx264 -c:a aac -crf 23 -b:a 128k -movflags +faststart "%~nf.3g2". This is particularly useful when processing multiple AVCHD clips from a camcorder, each saved as a separate M2TS file.
Technical Notes
M2TS is a broadcast-grade container capable of carrying multiple video, audio, and subtitle streams simultaneously — a feature set that far exceeds what 3G2 supports. During this conversion, the muxer discards all but the primary video and audio stream, and re-encodes both: video through libx264 at CRF 23, and audio through the AAC encoder at 128k stereo. The 3G2 format is structurally based on the MPEG-4 Part 12 ISO base media file format (like MP4 and MOV), which is why the -movflags +faststart flag — normally associated with MP4 — applies here as well. One notable limitation is that 3G2 does not support resolutions beyond what was standard for early mobile devices (typically 176x144 or 320x240 for the era), though modern decoders are more permissive. If you are converting full 1080p Blu-ray M2TS content, you may want to add a scale filter (e.g., -vf scale=640:-2) to the FFmpeg command to reduce the resolution to something appropriate for the target device. Chapter markers and Blu-ray navigation metadata present in M2TS are also silently dropped, as 3G2 supports neither. File sizes will typically shrink dramatically — a 30-minute M2TS file at 25 Mbps (roughly 5.6 GB) might compress to under 200 MB at CRF 23, depending on content complexity.