fast video for iphone encoding?

[moxie]

I just downloaded the latest ffmpegx and attempted to encode a .avi file for iphone. The first time, it came out white, so I searched through forums and found that I should uncheck the "decode with Quicktime" box. Did that, tried again. Now I have both picture and sound, but the audio runs at normal speed, and the video runs at double speed. Halfway through the video, picture switches to white, and audio continues normally to the end. I'm using the standard presets (exept for the quicktime part). The only thing that I can see that looks like it should help is framerate on the video tab, but I'm already on the slowest (NTSC film, 23.976). I really have tried searching the forums, and I'm probably missing something obvious, but I'd really appreciate any help. I'm not that savvy on this stuff :-)

[Case]

Install Perian (a multi-format decoder plugin for QuickTime) to extend QuickTime's ability to read more type of files. Test Perian's advantage by playing the source file in QuickTime Player.
Next, convert for iPhone with ffmpegX with decode with Quicktime activated.