search for: 1200kbps

hi all, i have been trying to export some videos using firefogg in two pass mode. the problem i get recently with various files is that when i choose a low bitrate (for example 1200kbps for a 512x224 25fps video with so many details) the video quality is very very good at the beginning (much better then my quality based -v 5 export which produces a 1204kbps video with the same build) and then the pixel blocks get bigger and bigger towards the end of the video and at the end they b...