Free online KUX to 3GP converter

A 3GP file is useful when an older mobile phone, MMS workflow, or legacy video application does not support the Youku-specific KUX format. Converting also reduces resolution and bitrate for devices with limited storage or playback capability.

What the KUX format is

KUX is a proprietary video format associated mainly with Youku desktop software and offline downloads. Youku applications create KUX files to store downloaded or cached video, and the files may contain proprietary headers, segmentation, or encryption. You usually encounter KUX files after downloading videos from Youku rather than when exporting video from a camera or standard editor.

KUX is not interchangeable with MP4, so changing the filename extension does not convert it. A decoder must read the KUX container and, where applicable, remove or process its protection before a normal video encoder can create 3GP.

What the 3GP format is

3GP is a compact multimedia container designed for older 3G mobile phones and low-bandwidth networks. It commonly stores MPEG-4 Part 2 or H.263 video with AAC or AMR audio. Its low bitrate and small frame sizes can produce much smaller files, but modern phones and editors generally support MP4 more reliably.

Choose 3GP when the receiving device specifically requires .3gp, supports only older mobile-video profiles, or has limited storage and processing power.

How to actually convert KUX to 3GP

Use the built-in online converter

1. Open the KUX-to-3GP converter on 101convert.com.
2. Upload the .kux file and select 3GP as the output format.
3. Choose a low-resolution profile such as 176×144 or 320×240 if the destination is an older phone.
4. Start the conversion and download the resulting .3gp file when processing finishes.

This option requires no software installation. Conversion can fail if the KUX file is encrypted, incomplete, or tied to an account-protected Youku download.

Use FFmpeg when the KUX file is readable

Install a current FFmpeg build, open a terminal in the directory containing the file, and test whether FFmpeg recognizes the KUX stream:

ffmpeg -i input.kux

If FFmpeg identifies video and audio streams, create a broadly compatible 3GP file with MPEG-4 Part 2 video and AAC audio:

ffmpeg -i input.kux -map 0:v:0 -map 0:a:0? -vf "scale=320:240:force_original_aspect_ratio=decrease,pad=320:240:(ow-iw)/2:(oh-ih)/2" -c:v mpeg4 -tag:v mp4v -b:v 250k -r 15 -c:a aac -b:a 32k -ar 8000 -ac 1 -f 3gp output.3gp

For a very old handset that expects QCIF video, use 176×144 and a lower bitrate:

ffmpeg -i input.kux -vf "scale=176:144" -c:v h263 -b:v 120k -r 15 -c:a aac -b:a 24k -ar 8000 -ac 1 -f 3gp output.3gp

If FFmpeg reports Invalid data found when processing input or cannot identify any streams, that build does not support the particular KUX variant. Use the 101convert.com converter, or obtain a standard MP4 download through the official Youku software where that option is available, then convert the MP4 with the same FFmpeg command after replacing input.kux with input.mp4.

Quality and compatibility limitations

Conversion cannot recover detail already discarded by the KUX source. Scaling to 176×144 or 320×240 and using a low video bitrate reduces file size but causes blur and block artifacts; keep the original KUX file for archival use.

Older phones may reject 3GP files containing AAC audio or MPEG-4 video even though those streams are valid in the 3GP container. For such devices, use the handset manual's required codec, frame size, frame rate, and AMR audio settings. If the target accepts MP4, MP4 with H.264 video is normally a better-supported alternative.

Some KUX downloads are encrypted, account-restricted, or incomplete cache fragments. No converter can reliably process a file that does not contain a complete playable video stream.