When you crop a MPG with TMPEG does it reduce the quality?

[garibaldo]

When I captured a video there were some tracking lines at the very bottom that I couldn't get rid of. I want to create a VCD that I can later incorporate into a DVD-R. I captured at 640x480 in Virtual Dub and then I converted to the NTSC VCD Standard in TMPEG. The output video appears to be letterboxed. I tried using the crop line feature in TMPEG to remove the very bottom of the video, but that required me to remove the top and bottom black bars too. The output video has black bars again, but the bottom of the video has been successfully removed. My problem is that I'm not sure if the quality has been reduced or not. It seems like it has. Why would the quality be reduced anyways? I'm just cutting out some of the video, not changing the rest of it, right?

[dinesh]

Tracking lines are normal in VHS capture. If you are going to view the VCD on TV, they should usually be off the visible area.
Why did you letterbox? VCD NTSC Specs require your video to be 352x240. You would have been better off Resizing. The original video could be opened in VirtualDub, crop the bottom lines off and Resize, and frame serve to TMPGEnc.
Quality would be reduced if your source itself is a MPG lossy format. If possible I would suggest you work as mentioned above on your original captured AVI video.