In Microsoft Windows Media Player 9 or 10, you may experience a color smearing or bleeding effect when you play some MPEG4 videos. This behavior often occurs when the video contains fast-moving scenes of varying colors. This problem occurs because of an issue with the way that the MPEG4 codec handles motion vectors. Sometimes, the decoder mistakenly uses invalid motion vectors.

Windows Media Player 9 or 10 FIX: MPEG4 videos