Does this OPlayer HD play avi and RMVB formats? or I still have to convert to mp4 first.

certainly, you should convert the videos to iTunes recognized formats for iPad, you may use Foxreal video converter to make it, which supports a wide range of video formats, like TiVo, MXF, MKV, MTS, M2TS, TS, MOD, TOD, FLV, F4V, AVI, WMA, QuickTime MOV, VOB, MP4, MPG, MPEG, SWF, ASF, MVI, VP6, EVO, VRO, DV, MP3, AC3, MKA, WMA, WAV, M4A, OGG, APE and more.

It also has many iPad special presets to make your operation much easier, as follows