What is a good DPG converter to convert to avi to dpg?
I found this AVI to DPG converter called 4Media DPG Converter is a good choice.

It can convert almost all video and audio formats to DPG/DPG2/DPG3/DPG4 videos or MP3/MP2 audios for playback on Nintendo DS. The following guide will show you how to convert AVI to DPG converter step by step.

First, free download, install and run this AVI to DPG converter.

Step 1: Load files

Click "Add File(s)" button on the toolbar or "File > Add File(s)" to load the AVI files you want to convert. Or click "Add File(s)" in the "Getting Started" to load AVI files directly.

You can also click "File > Add Folder" to select the folder you want to add, then all AVI files in the folder will be loaded into the file list.

Step 2: Choose output format and folder

Choose the file, click to open "Profile" drop-down list in the "Target Profile" column or at the bottom of the main interface, then choose the format you want.

Click "Browse" button to choose the destination folder for saving the output files.

Tip1: Click "Snapshot" button below the preview window on the right-bottom of the main interface to take a snapshot during preview to save as BMP file.

Tip 2: You can double click the loaded file in the file list to view the file information.

Tip 3: If you want to do more with your video and audio files before converting, please go to Step 3, otherwise jump to Step 4.

Step 3: Adjust output settings

1. Add multiple profiles for the same source file

Select the file and click the "Add Profile" button to add a default profile to the file, then select the profile you want from the "Profile" drop-down list. In this way, you can get them converted in one click.

2. Customize output file size with Bitrate Calculator

To customize the output file size, select the video file and click "Tools >Bitrate Calculator", and input the file size you want, then the video bit rate will be calculated. Click "OK" button, the size you enter will be displayed in the "Output Size" column.

3. Set the output parameters

On the "Profile Settings" panel, you can set the following parameters: Name, Video Size, Video Quality, Audio Quality, Channels. Click "Show Advanced Profile Settings" button to expand the "Advanced Profile Settings" page, in which you can set more parameters for satisfying more needs.

Step 4: Convert

After the above settings, click "Convert" button on the toolbar to start converting. You can pause, resume or stop the conversion at any time, and view the progress from the progress bar at the bottom.

After conversion, you can click "Open" button on the bottom to view the output files directly.

See more details about this AVI to DPG converter
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Hope these can help.