I didn't even know the Genesis could play videos. My wife got a Genesis 5.0 with the Ultimate package about 2 months ago, and we're still learning stuff about the car.
Back on topic, I'm not sure which model cars the other members have here, but in the case of my wife's car, I was able to get 1280x720 WMV video to play. The specific parameters (from Adobe Premiere Pro settings):
1280 width
720 height
29.97 frames per second
6.0 megabits per second (total constant bit rate)
5.872 megabits per second video (constant bit rate)
0.128 megabits per second audio, 48 khz audio rate (constant bit rate)
video - windows media 9
audio - windows media 9.2
6 mbps is overkill, 4 mbps to 5 mbps should be enough.
I was unable to get H.264 MP4 video to play, with either variable bit rate (5mbps target, 6mbps max) or constant bit rate (5 mbps). I'm not sure if this was an issue with the video or the audio, since my only choice for audio is AAC. The MP4 format I use works with Android smart phones. I'm not sure what MP4 format the Genesis will work with.
I uploaded a 2 minute test video at the link below. It's an 88MB video of my radio control glider (hence the persona rcgldr) at a local slope site where's there's a updraft when the wind blow towards the slope. Again the 6mbps was overkill, but I wanted to see if this would work. This video was made with the settings I listed above. At 88MB, it may not be worth downloading / viewing / transferring unless you're interested in radio control models or a nice view of a small canyon from the slope ridge.
http://rcgldr.net/rc/jrs6mbs.wmv
As mentioned in some other posts here, I'm not sure how practical the videos are (although it is cool). I'd be concerned about sitting with the engine running for extended periods of time (carbon monoxide hazard even if the engine doesn't overheat?), or with the engine off and the drain on the battery while watching a video.