MJPEG to 3G2 Converter

MJPEG to 3G2: The Codec Choice Decides Everything

3G2 is the 3GPP2 file format, specified in C.S0050-B and published in May 2007 for CDMA2000 multimedia services. It is an ISO base-media container carrying the brand 3g2a, deliberately constrained so that handsets, MMS gateways and in-vehicle units of the CDMA era could decode it. MJPEG is the opposite kind of file: a run of complete JPEG pictures, one per frame, with no inter-frame compression at all.

Everything that determines whether the resulting .3g2 plays on your target device comes down to the Video Codec you pick. The page opens on H.264. Choosing H.263 instead changes the frame size out from under you, in a way that is worth understanding before you click Convert.

Two Things a .mjpeg File Does Not Tell Us

An MJPEG stream is a concatenation of JPEG frames. It has no container header, which means two specific consequences here.

It has no frame rate. The decoder reads a sequence of pictures and assumes 25 frames per second, because that is the default for a JPEG sequence. If your camera or capture card recorded at some other rate, the output plays at the wrong speed and there is no frame-rate control on this page to correct it. A measured example: a three-second, thirty-frame sequence recorded at 10 fps came back as a 1.200-second clip at 25 fps, with all thirty frames intact and only the timing invented.

It has no audio track, and cannot have one. MJPEG carries pictures only. The .3g2 you get will be silent whatever you choose under Audio Codec, so the codec choice there matters only if you plan to add a track later in an editor.

If a .mjpeg or .mjpg file of yours does report a proper frame rate and does contain sound, then it is not a raw MJPEG stream at all — it is an AVI or QuickTime file with a Motion JPEG track and a misleading extension. Those convert normally, timing and audio included.

How to Convert MJPEG to 3G2

1. Upload Your MJPEG File: Drag the .mjpeg onto the page or click "Add Files" to browse. Several files can be queued and they all share the same settings.
2. Choose a Video Codec: The list is H.263, H.264 (which the page opens on), MPEG-4 and Xvid. The comparison below explains what each one does to your frame size and which device generation it suits.
3. Set the Resolution, and Trim if Needed: Video resolution opens on Keep original. Use Width x Height for a genuine handset frame such as 176 x 144 or 320 x 240, or Preset Resolutions for 240p and 144p. Trim stays on Unchanged until you switch it to Time Range and enter a start and a duration.
4. Convert and Download: Click Convert and save the .3g2. Files are uploaded over an encrypted connection, re-encoded on our servers and deleted automatically after a few hours — no sign-up, no watermark.

The Four Video Codecs, Compared

The H.263 behaviour is the one that surprises people. That codec defines a closed set of picture sizes and refuses anything else outright — raw ffmpeg simply fails to open the encoder if you hand it 640 x 480 — so rather than failing the job, the pipeline picks a legal size for you. The cost is that a 16:9 source becomes 4:3: 1920 x 1080 lands at 704 x 576, visibly squashed. If you want H.263, decide the frame yourself with Width x Height and choose one of the five legal sizes, and the snap will land exactly where you meant it to.

Audio Codec Options

Two caveats. First, none of the three is dependably preselected — the page's underlying default value does not correspond to any of the listed entries, so treat the audio codec as something to choose rather than something already chosen. Second, and more decisively here: your MJPEG source has no audio, so on this page the choice does not affect the file you get. The CDMA-native speech codecs the 3GPP2 specification names — EVRC, EVRC-B, EVRC-WB, 13K (QCELP), SMV and VMR-WB — are not offered as encode options at all.

Frequently Asked Questions

Why does my converted clip play too fast or too slow?

Because a raw MJPEG stream stores no frame rate and the decoder assumes 25 fps. If the frames were captured at 10, 15 or 30 per second, the output is stretched or compressed in time by exactly that ratio — a 10 fps capture becomes 2.5 times too fast. Every frame is present and correct; only the timing is wrong. There is no frame-rate control on this page to override it, so the fix is to re-wrap the stream at the correct rate in a desktop tool such as ffmpeg before uploading, or to accept the timing and adjust it in an editor afterwards.

What is the difference between 3G2 and 3GP?

They are siblings from two different standards bodies. 3GP was defined by 3GPP for GSM and UMTS networks; 3G2 was defined by 3GPP2 for CDMA2000 networks in C.S0050. The video codec lists overlap almost entirely — MPEG-4 Part 2, H.263 and H.264 — but 3G2 additionally permits the CDMA speech codecs while excluding some of the audio types 3GP allows. If your target device was on a CDMA network, this is the right page; if it was GSM, use MJPEG to 3GP instead.

Why was my resolution setting ignored?

You chose H.263. That codec accepts only five picture sizes, so the pipeline snaps your frame to the largest legal one that fits inside the source, and that snap overrides the Video resolution selection completely and does not preserve the aspect ratio. It is not a bug so much as a consequence of the codec — the alternative would be the job failing, which is what raw ffmpeg does. Select H.264, MPEG-4 or Xvid and your resolution choice is honoured exactly.

Will the file be much smaller than the MJPEG?

Almost certainly, and dramatically so. Motion JPEG compresses each frame on its own and stores no motion information at all, so a static shot costs the same per frame as a fast-moving one. Every codec on this page uses inter-frame prediction, which on typical footage is where most of the saving lives. The frame size you choose matters just as much: a 3G2 aimed at a handset is usually a small frame at a low bitrate, and the combination is what makes these files tiny.

Should I still be converting anything to 3G2 today?

Only if you have a specific reason. The CDMA2000 networks 3G2 was designed for have been shut down, so the format's original audience is gone; what remains is legacy hardware, archival playback and the occasional MMS gateway or embedded unit that still expects it. If the destination is anything from the last decade, MJPEG to MP4 is the better target — same H.264 video, a container everything decodes, and none of the codec archaeology this page requires.

What frame size should I choose for an old handset?

176 x 144 (QCIF) set through Width x Height is the safe answer for a feature phone; essentially every 3G2-capable handset decodes it, and it happens to be one of the five sizes H.263 accepts, so the snap lands exactly there. For a later CDMA smartphone, 320 x 240 (QVGA) with H.264 looks considerably better and is still widely accepted. Going above 352 x 288 for genuinely old hardware is the most common reason a device lists a file but refuses to play it.

Is the picture re-encoded, or are the JPEG frames kept?

Re-encoded, always. The JPEG frames are decoded to pixels and compressed again with whichever codec you selected, so this is a second lossy generation on top of whatever the MJPEG capture already discarded. There is no pass-through path here. On MJPEG sources that is usually an acceptable trade because the source is inefficient rather than pristine, but if you plan further editing, keep the original.

Why does my capture card's .mjpeg file open here but not in my player?

Because most consumer players decide what to do with a file by its extension and never learned that .mjpeg means a bare JPEG sequence. The decoding here happens on our servers with a build that recognises the stream by its contents. VLC and mpv will usually open one too if you force it; Windows Media Player and most smart-TV apps will not. Converting it into a real container is precisely the fix.

How are my files handled during conversion?

Your .mjpeg is uploaded over an encrypted connection, decoded and re-encoded on our servers, and both the upload and the resulting .3g2 are deleted automatically after a few hours. Nothing is shared or made public, and there is no sign-up, no watermark and no account required. Because MJPEG is uncompressed between frames, these files are large for their running time — if you only need a section, the Trim control cuts it during the same job.