First thing to try is render using one of the standard DVDA templates and create a DVD in DVDA. If that fixes your problem then use DVDA. If it doesn't, check back with specific questions.

/jerry

What are DVDA templates???
I render in Vegas using MPEG-2 and choosing DVD-PAL in the popup menu in the Settings window. Then I set the audio frequency to 48 kHz and choose to use closed GOPs. Then I demux the resulting MPEG-2 video and use it in DVD-Lab Pro.
To what I know, it should be enough.

One key question - if you look at the DVD where you have a motion issue, if you repeat it does it happen in exactly the same place ? How about if you play in slow motion - does it show it in the same place ? If it moves around and is not exactly the same each time, that does sound like a bitrate issue - the player can't read the data fast enough from the media. You may have the bit rate too high, poor quality media will also cause that issue or media that is just not compatible with that player - some are more particular than others. If the defect is in exactly the same spot each time (and shows in slow motion as well) then it is most likely part of the stream indicating an encoding problem but if it moves around it is more likely the data rate issue.

mikey

MPEG2 encoding is as much an art as it is a science.

Choose the "DVD Architect PAL video stream" or "DVD Architect widescreen PAL video stream" template and hit the "Custom" button, make sure the "Quality" slider is at "31", this setting determines the quality of the motion search algorithm not the video image quality. This might be a factor in your problem. It may also be that you aren't optimizing the bitrate for your particular project. Using two-pass VBR and plugging in the correct numbers will go a long way toward maximizing image and motion quality. How long is the project?

Also, using either of these templates will produce an MPEG2 program stream without audio. You will then render the audio for your project separately either using the WAV format or the AC3 Pro format. You will end up with separate video and audio streams and won't need to demux. If DVD-Lab only accepts elementary (m2v) streams, then in the custom setting for the video encoder, check the box on the "System" tab that says, "Save as separate elementary streams."

@mikey: The motion defects affect short intervals always at the same point, so it sounds like an encoding problem. But what's the cause? The strange thing is that the same video worked well some days ago. Then I added some minor cuts and set the audio channels to 'combine' in order to fix audio playback on stereo players having a wasted loudspeaker, and then it all began.

@John Cline: my project is 40 minutes long

What's going on visually at the exact moments that the defects are appearing?

For a 40 minute project, a CBR setting of 8,000,000 should work fine. Just make sure the quality slider is maxed out at "31."

The quality slider is set at 31.
Well, that's what happens... there are some intervals (fortunately short and not so frequent) looking like they had dropped frames... you see the motion frame by frame instead of seeing it smooth. However the bitrate is set to more than 9000. I didn't set it to this value, it was the default choice.