Strange pixelation/vertical lines after MPEG4/H.263 encode

I have been trying开发者_StackOverflow to encode video data (H.263 and MPEG4) from a USB camera on an embedded device. The device has a special hardware to do it.

But after encoding the raw video from the USB camera (H.263/MPEG4) the video quality becomes bad and some strange pixelations and vertical lines occur in the video. In this image you can see the annoying vertical lines. The second image is an example of displaying the raw video and the encoded video together; the right side is the display result from raw data (good quality), and on the left side is after encode. Is this problem a known pattern ? What causes these vertical lines ?

The properties of USB video data: 15 fps, QCIF, YUV420P.

By the way the image quality becomes a lot better when I display the video on a half-width area (with SDL); that is displaying the QCIF video on a 88x144 rectangle. The quality doesn't change when I change the height of the display area.

Thanks.

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seems like bad image format conversion, especially wrong width/height or strand parameters