At the moment (as far as I know) there is no android program to convert a VS4 file to avi/mp4.
So you will have to make one yourself....
Like
User9475 was already saying: "you have to download the free Android Studio, and write an Android app."
It can be just a very simple program.
Next to making a program, it also very easy to change the VS4 files by hand with a good hex-editor. Or of course convert it on a pc and move it to your phone/tablet.
You can download my (pc) program to convert the VS4 files from my Google Drive folder:
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Of course there is no way to use this MP4 file in the Poker game. You can use this MP4 file to see if an opponent is worth to buy.