Xbox 360 audio ok, video slow

[kanashiinosekai]

I've been using PMS almost a year and with the last xbox update the playback of some videos is slow, the playback starts fine but about 5 seconds later the video is slow, only the video, I've been trying a lot of things but I can't fix the problem... some advice? I use avisynth/mencoder only cause the video quality is better, with mencoder the problem is the encode speed with the videos that suffer the problem with avisynth