What else can you do.
One simple command:
ffmpeg -y -i movie.dav movie.mp4
will turn your dav file into mp4 file, which you can play on any player.
But what if you don't want to know what is ffmpeg, don't want to download and install it, don't want to learn how to use it ?
There is an app for it :D
Yes there are applications for Android which use ffmpeg and provide you a convenient interface for it - well some not so convenient because they would just expect you to provide them with the command you want ffmpeg to run, but others will have a GUI which will let you select your options and they will do the rest.
So in the Google Play Store search for ffmpeg and try some of the applications that will come up as a result.
Here is an application that does only that and some more because it will convert any video format to mp4 not only dav: