Free online KUX to MKV converter

You may need this conversion when a downloaded Youku video will not open in a standard media player or needs to be edited and archived in a broadly supported container. MKV can preserve the available video, audio, subtitle, and metadata streams without requiring the original Youku application.

What the KUX format is

KUX is a proprietary video container used by Youku, particularly for videos downloaded through Youku applications. It commonly contains an FLV-like stream with Youku-specific obfuscation or encryption, so ordinary players and general-purpose converters may reject it. KUX files are most often encountered in Youku download folders, cached offline-video directories, or exports from older Youku desktop software.

What the MKV format is

MKV, formally Matroska, is an open multimedia container that can store H.264, H.265, VP9, AV1, AAC, Opus, subtitles, chapters, and multiple audio tracks. It is supported by VLC, MPV, Kodi, Plex, many smart TVs, and most modern editing or remuxing tools. MKV is useful when you want one file containing several streams or need a container less restricted than the original application format.

How to actually convert KUX to MKV

Use the built-in online converter

1. Open the KUX-to-MKV converter on 101convert.com.
2. Select the .kux file and choose MKV as the output format if the converter does not select it automatically.
3. Start the conversion, then download the resulting .mkv file when processing finishes.
4. Open the result in VLC or another MKV-compatible player and check the complete duration, audio, and subtitles.

This option requires no software installation, but a KUX file that is still encrypted, incomplete, or unsupported by the service may fail to convert.

Try FFmpeg locally

Install a current FFmpeg build, open a terminal in the folder containing the video, and test a stream-copy conversion:

ffmpeg -i input.kux -map 0 -c copy output.mkv

-map 0 attempts to include every detected stream, while -c copy remuxes the media without re-encoding. If FFmpeg reports that it cannot determine the input format, the KUX variant is not directly supported by that build; changing the extension alone will not decrypt or convert it.

If the streams are recognized but copying produces an incompatible file, transcode to broadly supported codecs:

ffmpeg -i input.kux -map 0:v:0 -map 0:a? -c:v libx264 -preset medium -crf 18 -c:a aac -b:a 192k output.mkv

The optional audio mapping prevents failure when the source has no audio stream. Transcoding takes longer and can reduce quality, but it can resolve codec or timestamp compatibility problems.

Quality and compatibility limits

Container conversion does not improve a KUX file's original resolution, bitrate, or compression quality. Use stream copying whenever it succeeds; re-encoding introduces generation loss and may remove unsupported subtitles or metadata. Some KUX downloads are split into segments or protected for playback only inside Youku, and those files cannot be converted reliably without an authorized decoder or a complete, unprotected download. Verify the output with ffprobe output.mkv or a media player before deleting the source.