When a DVD movie shows mpeg artifacts, samll pixelation blocks, or even mosaics, we can be sure that the MPEG video stream was not encoded in good quality. There are different levels of MPEG encoders. Consumer level encoders, either software or hardware, usually don't have the complex algorithms that are needed to calculate where the bits are distributed most efficiently to, and how precise the motion detection and the motion prediction are achieved. Remember, MPEG has a very high compression ratio. The compressed video quality totally depends on the quality of the MPEG encoder. In MPEG-2 video stream, frames are organized into GOPs, i.e. group of pictures. In a GOP, the first frame called I frame is the only real frame containing most of the pixels. The next 4 or 5 B frames and the last P frame are all predicted frames from the I frame. In general, VBR (variable bitrate) is superior over CBR (constant bitrate), unless the CBR is set to the highest bitrate, in which case the video on one DVD disc is only 60 minutes or shorter at transfer rate of over 9000 kb/second. VBR can achieve better quality and much longer play time by saving bits in darker scenes with less motion for brighter and more dynamic scenes. Simply because the bright and dynamic scenes require more bits. Multiple VBR encoding is superior over single pass VBR, because the multiple pass encoding is able to correct the errors made by the first or previous caculation(s) resulting in the best possible quality. This comparison is within the same level of encoders. The whole process is actually much more complicated than what we can explain here, just keep in mind: the lower-end the encoder is, the less acurate calculation for motion detection/predction the encoder is capable of, thus the lower quality of the video.

Some people blame the DVD player that shows pixelation for not playing at the right speed. As a matter of fact, there is no speed issue in DVD video. When the DVD player is playing a disc, the video, audio, and information data is loaded into the buffer memory, then the processing chips draw the data from the memory. Finally, the processed audio/video signal is output to the display device like a TV.