Do you not have the source file? Would be so much better quality if you did. That said if it is some vintage file you or yours converted back when and source long since gone then you can certainly play.
Anyway DPG, not sure why we are in the 3ds section but here, is most commonly associated with moonshell on the DS.
There are a variety of takes but in reality is probably one of the simplest video formats you can get, actually to its detriment but your boon here.
Earlier DPG which I am more familiar with (many years ago I had a fork of batchdpg) is basically an MPG video stream concatenated (as in one after the other, most video is interleaved, or if you prefer what does the I and AVI stand for, so that the audio and video come from the same place on the disc to avoid seeking or random reads, not as bad on SD card as it is on a DVD or something but still not ideal) with an MP2 audio file (was too slow for MP3 and video at the same time, though later stuff might have managed it at seriously low bitrates/quality), and maybe a header.
DPG3 I believe added some kind of extra info on various elements and some alternative audio options but still fundamentally the same thing.
I don't know offhand if MPG and MP2 audio have headers or magic stamps you could read to determine the lengths of the elements, and if not I believe the main DPG header will include some kind of lengths or locations you can use to slice it out.
Anyway get the individual streams and you can convert them to your chosen format, or mux them into a more normal MPG and play that on most things without necessarily losing any quality (MPG was never good, and resolutions here are not going to help it, so my advice would be do as few conversions as you can).
