How to remember playback location of MP4

[Compact101]

I have started trying out DSub as a newbie to Subsonic (coming from Mort Player and Plex)

With DSub I can save files to my mobile to listen to when I'm out and about. However the player rarely remembers the location of where I am up to, when I listen to one of the books, which is in MP4

Is there a trick to doing this? I have read a post about bookmarks but can't see it when i am playing a track.
I notice that my Dsub uses other apps to play the actual track (In mycase ES Player) could this be the reason it is not book marking it?

if so Should I change all my audiobooks to a different format i.e from MP4 to MP3 or MP4b?
Or would a different using a different app to play it work?

Thanks

[daneren2005]

DSub has no ability to track what third party apps play, so if you are playing it in a third party app bookmarks will most definitely not work. It probably kicks you out to a third party app because mp4 is traditionally a video format and DSub does not support videos directly. If it is an audio format, yes, I recommend converted it to mp3 so that DSub can play it directly if you want it to remember where you left off at.