Free online KUX to M2T converter

What the KUX format is

KUX is a proprietary video container associated with Youku downloads and playback software. Youku desktop applications create or save KUX files for offline viewing, often alongside segmented or protected download data. KUX files commonly contain H.264 or other internet-delivery codecs rather than the MPEG-2 video expected by HDV-oriented software.

Because KUX is not a broadly standardized container, support varies between FFmpeg builds and media players. A file may also be encrypted or incomplete if it was copied from an application cache instead of exported as a finished download.

What the M2T format is

M2T, usually identified by the `.m2t` extension, is an MPEG-2 Transport Stream file used especially by HDV camcorders and editing systems. It can carry MPEG-2 video and MPEG audio in a stream designed for reliable transport and recovery from transmission errors.

M2T is useful when an editor or device specifically expects HDV-style transport streams. It is not inherently smaller than KUX: converting to the usual MPEG-2 video format often increases file size because MPEG-2 uses a higher bitrate than web-oriented codecs at comparable visual quality.

How to convert KUX to M2T

The most practical desktop method is FFmpeg. First test whether the installed build can read the KUX file:

ffprobe input.kux

If FFprobe reports video and audio streams, convert to an MPEG-2 transport stream with MPEG-2 video and MPEG Layer II audio:

ffmpeg -i input.kux -map 0:v:0 -map 0:a:0? -c:v mpeg2video -b:v 25000k -maxrate 25000k -bufsize 17825792 -pix_fmt yuv420p -c:a mp2 -b:a 384k -ar 48000 -f mpegts output.m2t

The 25000k video rate approximates common HDV data rates. Adjust the rate, frame size, and frame rate to match the target editor or device; HDV workflows commonly use 1440×1080 at 25 or 29.97 frames per second, while other MPEG-2 transport-stream workflows accept different dimensions.

If the source is already compatible with the required transport stream, a remux may avoid re-encoding, but this is uncommon for KUX:

ffmpeg -i input.kux -map 0 -c copy -f mpegts output.m2t

Use this only if the destination accepts the source codecs and FFmpeg completes the operation without codec or timestamp errors. For a no-installation option, upload the file to the free converter on 101convert.com and select M2T as the output format.

Quality and compatibility limits

Transcoding cannot restore quality lost in the original KUX encode. Keep the original KUX file, and use a sufficiently high MPEG-2 bitrate to limit a second generation of visible artifacts. The conversion may also change subtitles, multiple audio tracks, chapters, variable frame rate behavior, or embedded metadata; the command above selects the first video and first audio stream only.

If FFprobe cannot identify the KUX streams, the file is likely protected, incomplete, or unsupported by that FFmpeg build. A converter cannot process encrypted Youku data without a compatible decoder; obtain a playable, legally accessible source through the application that downloaded it, then convert that source. Check the resulting `.m2t` in the intended editor before deleting the original, because some systems require a specific HDV frame size, frame rate, bitrate, or audio format.