Seems the C280 uses the rockchip part of the processor... then audio have to be MP2 instead of MP3.
Then key parameters are:
video format: XVID, any bitrate around 1100 is ok
fps: up to 25... 20 recommended for better sound synchronization
resolution: 320x240
audio format: MP2, any bitrate 128 is ok
sampling up to 48k
All this is easily managed by AVIConverter, a free converter that has this parameters hard coded.
Search for it in
www.mympxplayer.org, in there is version 4.0
Good luck!!