Not sure what fast video format (anything practical for normal DS carts* is usually some flavour of DPG for moonshell, maybe the more limited AVI for tuna vids, or DSV for the wavelet player). Tunavids is lovely work but seldom used in anger (mpeg4 ASP aka xvid and divx to most people is not quite as capable when limited to the DS real time decodes as the MPEG1 of the DPG format).
*stuff like the DSTwo and ISMM have the option to play fairly normal formats at SD resolutions.