Free online KUX to OPUS converter

What the KUX format is

KUX is a proprietary container or encrypted media format associated with downloaded Kuwo Music or Youku content, depending on the source. Kuwo and Youku desktop or mobile applications create KUX files for offline playback, and the files may include access restrictions that prevent ordinary media software from reading them.

A KUX file can contain audio or video. The extension alone does not identify the exact variant, so conversion results depend on the application that created the file and whether the file has been decrypted or otherwise made accessible.

What the OPUS format is

OPUS is an open, lossy audio codec designed for speech, music, streaming, and low-latency communication. It provides good quality at relatively low bitrates and is supported by browsers, VLC, FFmpeg, messaging software, and many modern media players.

OPUS stores audio only. If the source KUX contains video, converting it to OPUS removes the video stream, subtitles, and other video-container data.

How to actually convert KUX to OPUS

Using the built-in online converter

You can convert the file on 101convert.com for free without installing software:

1. Open the KUX-to-OPUS converter on 101convert.com.
2. Upload the .kux file.
3. Select OPUS as the output format and start conversion.
4. Download the resulting .opus file after processing finishes.

If the service reports that the file is unsupported, the KUX is probably encrypted or uses a proprietary variant that requires playback or decoding by its original Kuwo or Youku software.

Using FFmpeg after the KUX is readable

FFmpeg can extract the audio when it has a demuxer and decoder for the particular KUX file:

ffmpeg -i input.kux -vn -c:a libopus -b:a 96k output.opus

-vn removes video, libopus selects the OPUS encoder, and -b:a 96k sets the audio bitrate. Use 128k or 160k for music when a larger file is acceptable.

If FFmpeg returns an invalid-data, unknown-format, or decoder error, play or export the media through the original Kuwo or Youku application first, if that application provides an export option. Then convert the resulting standard file, such as .mp4, .m4a, or .wav:

ffmpeg -i decoded-input.m4a -c:a libopus -b:a 96k output.opus

Quality and compatibility limitations

OPUS conversion is normally a lossy re-encode. Converting a KUX file that already contains compressed audio cannot restore lost detail; avoid repeated conversions and choose a bitrate appropriate to the source. The original Kuwo or Youku encryption, account restrictions, and regional playback rules may prevent conversion even when the file extension is correct.

For broad compatibility, keep the output as a standard single-track .opus file and use a common sample rate such as 48 kHz. Some older hardware players and basic editors do not support OPUS; use AAC or MP3 instead when those devices are required.