Aiseesoft DPG Converter for Mac is a video conversion tool that you can use to convert your video files to the DPG, DPG2, DPG3 and DPG4 formats. These are all formats that are often used for video playback on the Nintendo DS. They use MPEG-1 for video, and a few different codecs for audio, including WAV, MP2 and OGG. To play these formats on your DS, you need to have Moonshell installed. This is a homebrew program that allows you to play videos on your device.
This converter has excellent input format support. I opened MKV, AVI and H.264 files without any problems. Output format support is also great, and not restricted at all to DPG formats. The application includes a lot of conversion profiles for devices like the Xbox 360, Playstation 3, PSP, iPhone, iPod Touch, iPad, Wii, DS, and a few more.
There is a video editor that you can use to trim and crop videos, adjust their properties, and add watermarks to them.
I didn't have a Nintendo DS to test DPG files converted with this app. I tried opening them with MPlayerX but it doesn't support the format. The trial for this app lets you convert half of your videos if they are less than 5 minutes long. That should be enough for users to test the application to see if the files that it converts play well on the DS.