Free online MK3D to AVI converter

Some older players, editors, and devices accept AVI but do not recognize Matroska 3D files with the .mk3d extension. Converting the container can improve compatibility, but AVI may not preserve MK3D’s stereoscopic metadata.

What the MK3D format is

MK3D is a Matroska container variant designed for stereoscopic 3D video. It can store video, multiple audio tracks, subtitles, chapters, and 3D layout information such as side-by-side or top-and-bottom presentation.

MK3D files commonly come from 3D Blu-ray extraction and Matroska authoring workflows using tools such as MakeMKV and MKVToolNix. VLC, mpv, and other Matroska-capable players may open them, although correct 3D playback depends on the player, display, and stored layout.

What the AVI format is

AVI is an older Microsoft container supported by many legacy Windows applications, media players, and hardware devices. It can contain codecs such as MPEG-4 Part 2, Xvid, Motion JPEG, and uncompressed video.

AVI is useful when a target application specifically requires .avi or when compatibility with older software matters. It has weaker support for modern metadata, subtitles, chapters, variable-frame-rate video, and advanced 3D signaling than Matroska.

How to convert MK3D to AVI

Using FFmpeg

FFmpeg is the most controllable desktop option. Install a current FFmpeg build, open a terminal in the folder containing the source file, and inspect its streams first:

ffprobe input.mk3d

For a broadly compatible AVI containing the first video stream and available audio, run:

ffmpeg -i input.mk3d -map 0:v:0 -map 0:a? -c:v mpeg4 -vtag XVID -q:v 3 -pix_fmt yuv420p -c:a libmp3lame -q:a 3 output.avi

The command re-encodes video as MPEG-4 Part 2 with an Xvid-compatible AVI tag, converts audio to MP3, and uses yuv420p for broad decoder support. Lower -q:v values generally produce higher video quality and larger files; test values from 2 to 5 if needed.

To convert only the video and omit audio, use:

ffmpeg -i input.mk3d -map 0:v:0 -c:v mpeg4 -vtag XVID -q:v 3 -pix_fmt yuv420p output.avi

If the source contains several audio tracks, replace -map 0:a? with a specific stream such as -map 0:a:0. FFmpeg reports unsupported streams or codec errors in the terminal; subtitles and attachments normally should not be copied into AVI.

Using 101convert

You can also convert the file on the 101convert.com website for free without installing software. Upload the MK3D file, select AVI as the output format, start the conversion, and download the resulting file when processing finishes. Online conversion may impose file-size limits and may re-encode using fixed quality settings.

Quality and compatibility limitations

Conversion to AVI usually requires re-encoding, so it can reduce image quality and remove HDR, chapters, subtitles, attachments, or multiple audio tracks. The command above preserves the visible stereoscopic arrangement in the video frames, but AVI does not reliably preserve MK3D’s 3D metadata; select the corresponding side-by-side or top-and-bottom mode manually on the playback device.

AVI files larger than 2 GB can expose compatibility problems in older software. If the target program accepts another format, MP4 or standard Matroska is usually better for modern codecs and metadata. Keep the original MK3D file if you may need the original 3D structure, tracks, or lossless source quality.