Hi Centame,
Rockchip players require videos to be in a SPECIFIC screen size for them to play.
Have a look at this post here:
viDrop - free open-source converter for RockChip players - a lot of members have had success with converting their videos for their Rockchip player using ViDrop.
Also, can you UPLOAD your sample video to this site as well? Would be good to share this and see what your video settings are. You can upload it here -->
Uploads by Members.
Try that and let us know.