Convert KUX to MP4

Many phones, editors, media players, and sharing services do not accept Youku’s KUX downloads. Converting a readable KUX file to MP4 provides a more compatible copy for playback, editing, archiving, or sharing.

What the KUX format is

KUX is a proprietary video format associated with Youku. Youku desktop and mobile applications may create KUX files for offline playback, usually in application download or cache folders.

KUX is not a standard exchange format. Files can contain Youku-specific metadata, unusual stream arrangements, encryption, or other access controls that prevent ordinary players and converters from reading them. Changing .kux to .mp4 does not convert the file.

What the MP4 format is

MP4 is a widely supported container used by web browsers, phones, televisions, media players, and video editors. The most compatible combination is usually H.264 video with AAC audio.

MP4 is suitable for sharing and editing because it has broad hardware and software support. If the KUX file contains streams that MP4 accepts, remuxing can change the container without re-encoding and therefore without reducing video quality.

How to convert KUX with FFmpeg

FFmpeg is the best desktop first test because it is free and available for Windows, macOS, and Linux. Download a current build from the official FFmpeg site or install it through a reputable package manager.

1. Place the KUX file in an accessible folder and open Command Prompt, PowerShell, or Terminal in that folder.
2. Test whether FFmpeg can read the file:

ffmpeg -i input.kux

If FFmpeg identifies the video and audio streams, try a lossless remux:

ffmpeg -i input.kux -map 0:v:0 -map 0:a? -c copy -movflags +faststart output.mp4

-c copy copies the existing encoded streams without recompression. The command succeeds only when FFmpeg can decode the KUX input and the source codecs are valid in an MP4 container.

If the remuxed file has no sound, will not play on the target device, or uses incompatible codecs, transcode it to H.264 and AAC:

ffmpeg -i input.kux -map 0:v:0 -map 0:a? -c:v libx264 -crf 20 -preset medium -c:a aac -b:a 192k output.mp4

Lower CRF values generally produce larger, higher-quality video; values around 18–23 are common. Transcoding takes longer and can reduce quality, unlike remuxing.

Desktop converters with a graphical interface

Shutter Encoder provides an FFmpeg-based interface. Add the file and try Rewrap with MP4 as the destination when the program recognizes the KUX input. If rewrapping fails but the file is readable, use an H.264 conversion function and select AAC audio.

HandBrake can transcode a KUX file only if its underlying input libraries can read that particular file. It does not decrypt Youku downloads or bypass application protection, so FFmpeg should be tested first.

Online conversion

CloudConvert, Convertio, and Zamzar are reputable services, but KUX support is not guaranteed and can change. Use one only when its upload page explicitly accepts .kux files and identifies MP4 as an output format; an accepted filename extension does not prove that the service can decode the content.

Online conversion requires uploading the video and may impose file-size, duration, or processing limits. Do not upload private or copyrighted material unless you have permission and accept the service’s retention and privacy terms. A local FFmpeg or Shutter Encoder workflow avoids upload limits and keeps the source file on your computer.

Compatibility and protection limits

A KUX file that FFmpeg reports as unsupported, encrypted, or invalid cannot be converted by ordinary MP4 converters. A file that plays only inside the Youku application may be protected for offline playback rather than being a normal readable video container.

Use Youku’s official download or export option to obtain an MP4 or another standard format when available. Do not expect FFmpeg, HandBrake, or a file extension change to remove DRM or other access controls; conversion requires an authorized, unprotected source.