MyMPx.org - how do i find out what mp4 player i have?

HellNova, There are several different main processors used in these players the most common is the Actions Chipset which is what your player seems to be. Action players are single task capable and generally use the AMV video format although some of the earlier models used the MTV format which has a very poor compression ratio so the video files were very large. Some player s were capable of both formats but AMV seems to be the standard know. The big plus with the Action chip players is that there are quite a number of tools that can be used for firmware backup and theming etc. at least until the 9.0.XX series firmware came along but new tools are being created for these versions so it is expected that they will continue to be the most customisable.
The SigmaTel chipset players use the SMV video format which like the MTV format does not have terribly good video compression ratio so once again the video files can tend to be quite large. Although video conversion tools are available that is about all. The firmware for these players is very different and usually comes with it's own install software and I think there may even be a backup utility in the download section. SigmaTel generally produce good quality audio components so the audio on these players is said to be better quality but having never owned one i can not comment on that. Sigmatel firmware is very similar to Action firmware layout and feature wise and in most cases it is hard to tell the two apart as they can sometimes use the same images with in their GUI's but unlike the Action firmware can not be themed. once again these are single task capable.
Sunplus chip type players generally are used on players that incorporate some sort of optical camera feature. They use the ASF video format and there and are very firmware specific. trying to do anything to Sunplus firmware is generally a disaster and recovery of a dead Sunplus player is practically impossible as my understanding is that the firmware must be reinstalled at a factory level directly to the chip.
Finally there are Rockchip type players that use the AVI video format and are generally more powerfull than the others and are able to multitask which means you are able to do other things like play games or look at pictures etc while playing music at the same time. We do have a firmware loader in the Download section but there are no tools readily available for firmware backup and theming.
there are also players that are capable of playing NES rom games but once again I have no experience with these players so do not know their capabilities or components so can not comment to much on them but thet are growing in number so more should become known as users post their experiences.
To the best of my knowledge most of these chip types are able to support SD memory card fetures which make there capacity expandable but the Rockchip players seem to utilise this feature the most.

Hope this helps.