Free online KUX to AAC converter

What the KUX format is

KUX is a proprietary video container associated with the Youku desktop client and Youku downloads. It commonly stores downloaded or cached Youku video streams, including video, audio, and sometimes segmented or protected content.

KUX is not a general-purpose format, so many media players and editors cannot open it directly. Files obtained from newer Youku downloads may also use encryption or other protection that prevents third-party conversion.

What the AAC format is

AAC is a lossy audio codec used in MP4/M4A files, streaming services, mobile devices, and editing software. It generally provides better quality than MP3 at comparable bitrates and is supported by most current hardware and applications.

An .aac file normally contains a raw AAC stream, often in ADTS format, without video or a general-purpose container. For broader compatibility, an AAC track stored in an .m4a container may be preferable, but choose raw AAC when the receiving program specifically requires .aac.

How to actually convert KUX to AAC

The built-in converter on 101convert.com can process the file without installing software:

1. Open the KUX conversion page on 101convert.com.
2. Upload the .kux file.
3. Select AAC as the output format.
4. Start the conversion and download the resulting .aac file.

For local conversion, use FFmpeg if it recognizes the KUX file and the file is not protected. Run:

ffmpeg -i input.kux -vn -map 0:a:0 -c:a aac -b:a 128k output.aac

-vn removes video, -map 0:a:0 selects the first audio stream, and -b:a 128k sets the AAC bitrate. Use 192k or 256k when the source has sufficient quality and the output is intended for listening rather than low-bandwidth playback.

To inspect the input before converting, run ffprobe input.kux. If FFmpeg reports an unknown format, encrypted data, or no audio stream, the file cannot be converted by this method; obtain an unprotected playable source through the Youku application or use the online converter if it accepts that particular file.

Quality and compatibility considerations

Converting to AAC does not restore quality lost during the original Youku encoding. Re-encoding an already compressed audio track can reduce quality, so use the highest practical bitrate and avoid repeated conversions.

A raw .aac file may not contain metadata such as title, artist, or album art. If the target application accepts it, an .m4a output provides a more compatible container for metadata and chapter information.