Free online MK3D to MJPG converter

Some players, capture devices, and legacy editors accept Motion JPEG but cannot open a stereoscopic Matroska file. Converting the video stream to MJPG provides a broadly decodable, frame-based output, usually without carrying over MK3D’s 3D metadata.

What the MK3D format is

MK3D is a Matroska container variant used for stereoscopic 3D video. It can store video, audio, subtitles, chapters, and stereoscopic layout metadata such as side-by-side or top-and-bottom presentation. MK3D files are created by Matroska muxers and 3D video tools, including MKVToolNix-based workflows, and commonly appear in 3D video archives or downloads.

The extension describes the container and intended 3D use; the actual video codec may be H.264, HEVC, or another codec. A file may also contain 3D video in an ordinary .mkv container, so changing the extension alone does not convert it.

What the MJPG format is

MJPG, or Motion JPEG, stores video as a sequence of independent JPEG-compressed frames. An .mjpg file is commonly a raw Motion JPEG stream, although Motion JPEG is also frequently stored in an AVI container.

Independent frames allow simple decoding, frame-accurate cutting, and compatibility with some cameras, capture systems, embedded devices, and older editing software. MJPG normally requires much more storage than H.264 or HEVC at comparable visual quality, and a raw MJPG stream generally carries no audio or reliable stereoscopic metadata.

How to actually convert MK3D to MJPG

FFmpeg is the most direct desktop method. Install a current FFmpeg build, open a terminal in the folder containing the source file, and run:

ffmpeg -i input.mk3d -map 0:v:0 -c:v mjpeg -q:v 3 -an output.mjpg

This selects the first video stream, encodes each frame as Motion JPEG, removes audio, and writes a raw MJPG output. The -q:v value controls JPEG quality: lower values produce better quality and larger files; values from 2 to 5 are a practical starting range.

To retain the source frame rate and dimensions, FFmpeg normally does so automatically. To force a specific frame rate, add a filter such as -r 30; to resize, add -vf scale=1920:-2. For example:

ffmpeg -i input.mk3d -map 0:v:0 -vf scale=1920:-2 -r 30 -c:v mjpeg -q:v 3 -an output.mjpg

If the receiving application expects an AVI file rather than a raw .mjpg stream, use an MJPEG AVI container instead:

ffmpeg -i input.mk3d -map 0:v:0 -c:v mjpeg -q:v 3 -an output.avi

For a no-install conversion, upload the file to 101convert.com, choose MJPG as the output format, and download the converted file. Check the resulting file in the target device or editor because support for raw MJPG and MJPEG-in-AVI differs.

Quality, compatibility, and limitations

MK3D stereoscopic metadata is not reliably represented in a raw MJPG stream. If the source uses side-by-side or top-and-bottom views, the converted frames usually retain that arrangement as ordinary pixels, but the output may not tell a 3D player how to interpret it. If the source uses a codec or structure with separate left and right views, selecting 0:v:0 may convert only the first view.

Use ffprobe input.mk3d before conversion to inspect stream count, codec, dimensions, frame rate, and stereoscopic side data. Verify whether the target requires .mjpg raw video or an AVI container; renaming output.avi to output.mjpg does not change its container format.