I think the following configuration works well in Media Player on Mobile 5 based Pocket PCs. The configuration also works well in the freeware TCPMP (The Core Pocket Media Player) on "any" Pocket PC, as long as the TCPMP aac plugin dll has been installed...

[Pocket PC Mobile 5 Media Player]
Res1=320x240
Res2=640x480
Res3=160x120
Res4=512x384
ResAna1=320x180
ResAna2=640x360
ResAna3=160x90
ResAna4=426x240
NTSCFrameRate1=15
NTSCFrameRate2=10
NTSCFrameRate3=29.97
PALFrameRate1=12.5
PALFrameRate2=8.33
PALFrameRate3=10
PALFrameRate4=25
VCodec=xvid
ACodec=aac
ARate=24000
ABRate=48
Format=mp4
FileType=mp4
Quality=30