horizontal lines

[eva 01]

When the bitrate is not very high (500 to 800/900), and when there are fast movements on screen, I see some horizontal lines "flashing" at the screen. Does someone know what it is?
Thanks.

[Acaila]

Sounds like interlacing to me. You should read this (http://www.100fps.com) for an excellent overview, and then either follow the solutions provided there or search around this forum for a million and one discussions about it.