xvid video doubled in size

Hi,

Today I wanted to re-encode a video and I suddenly saw the size almost double. I still using xvid with Magix video deluxe.
When I opened it with SPlayer I see the Overall bit rate : 2 626 Kbps, for the Video Bit rate : 1 302 Kbps, Stream size : 19.6 MiB (50%).
The original file which is much small is Overall bit rate : 1 518 Kbps, Video Bit rate : 1 331 Kbps, Stream size : 20.0 MiB (88%).
The quality looks the same. I've tried with XVid 1.3.2 and 1.2.2.
Why is the size almost double? How kan I fix this?

Thanks.