I don't have a proper answer for you, but as a general rule it's advisable to render to still images and assemble your movie afterwards. If Poser should take it into its head to crash (perish the thought...) you can start again from where you left off. In addition, things like the white flashes might be easier to diagnose and/or maybe even fix. At a high frame rate, you could afford to drop those frames altogether. It's also better to render to a non-compressed file format. That should help your resolution - but I assume you know that animation render settings need not be the same as the ones you use for stills? Are you sure that anti-aliasing is really in force? No offence intended. It might help others answering this question to know what version of Poser you are using.