1. Use a high-quality audio file. First and foremost, make sure that the MP3 files you are using are of the highest quality possible. The higher the bit rate of an MP3 file, the better the sound quality will be.
2. Convert your MP3 files to WAV format. WAV files are lossless audio files, which means that they do not lose any quality when converted. To convert MP3 to WAV, you can use a free software tool like Audacity.
3. Use a high-quality video editor. When importing your WAV files into Windows Movie Maker, make sure to select the "High Quality" option in the import settings. This will help to ensure that the audio quality is preserved.
4. Render your video at the highest quality possible. When you render your video in Windows Movie Maker, select the "Best" quality option. This will help to ensure that the audio and video quality are preserved.
5. Upload your video to YouTube in high quality. When uploading your video to YouTube, select the "High Quality" option in the upload settings. This will help to ensure that the audio and video quality are preserved.
By following these steps, you can upload your game soundtrack to YouTube without losing any sound quality.