Free online MK3D to 3GPP converter

Phones and older mobile players that accept .3gp may not recognize an MK3D file. Converting it creates a more widely supported 3GPP copy, but the usual conversion produces a 2D video and may discard stereoscopic information.

What the MK3D format is

MK3D is the Matroska 3D video variant, using the Matroska container to store stereoscopic video, audio, subtitles, and 3D-display metadata. It commonly appears in Blu-ray 3D rips and other downloads containing left- and right-eye video views. Applications such as MakeMKV and mkvmerge can create or package this content, while media players such as VLC and MPC-HC can read many MK3D files.

The .mk3d extension identifies the intended 3D presentation; it does not guarantee that every decoder supports the underlying codec or that both eye views are stored as independently selectable streams.

What the 3GPP format is

3GPP is a mobile multimedia container normally saved with the .3gp extension. It was designed for phones and mobile networks and can contain video encoded with H.263, MPEG-4 Part 2, or H.264, together with AAC or AMR audio.

3GP is useful when a target phone, messaging application, embedded player, or legacy video editor specifically requires that container. H.264 video with AAC audio usually gives better compatibility and quality than the older H.263 and AMR combinations, but some older devices only support a restricted resolution, frame rate, codec profile, or audio format.

How to convert MK3D to 3GPP

Using FFmpeg on a computer

FFmpeg is the most controllable option because it can read Matroska containers and explicitly select codecs, streams, resolution, and compatibility settings.

1. Install a current FFmpeg build and verify that it includes H.264 and AAC encoding.
2. Inspect the source streams with ffprobe input.mk3d. Check whether the file contains one video stream or separate left- and right-eye streams.
3. For a broadly compatible 3GP file, run:

ffmpeg -i input.mk3d -map 0:v:0 -map 0:a:0? -c:v libx264 -profile:v baseline -level 3.0 -pix_fmt yuv420p -c:a aac -b:a 96k -ar 44100 -f 3gp output.3gp

-map 0:v:0 selects the first video stream, so this command intentionally exports one view when the MK3D file contains separate stereoscopic streams. The optional question mark on the audio map allows conversion to continue when the source has no audio.

For a smaller file, add a size and quality setting such as -vf scale=-2:480 -crf 25. Replace the H.264/AAC settings with -c:v h263 -c:a amr_nb only when the destination device requires those older codecs and the FFmpeg build provides the necessary encoders.

Using the online converter

You can convert the file on the 101convert.com website for free without installing software: upload the MK3D file, select 3GPP or .3gp as the output, start the conversion, and download the result. If the service exposes codec or resolution choices, use H.264 video, AAC audio, and the maximum resolution supported by the destination device.

Quality and compatibility limitations

Most 3GP players do not preserve Matroska stereoscopic metadata or MVC-style 3D structure. A normal 3GP export therefore displays only the selected eye or a decoder-dependent flattened representation; it does not remain an equivalent 3D master.

Subtitle tracks, chapters, attachments, multiple audio tracks, and advanced Matroska metadata are usually omitted because the 3GPP container and older mobile players support fewer track types. Keep the original MK3D file if stereoscopic playback or archival quality matters.

If FFmpeg reports that the MK3D video codec cannot be decoded, first remux or decode it with a player or encoder that supports that particular 3D stream; changing the filename extension cannot convert the codec.