MP4 files store compressed audio and video on your computer. The file format works with a variety of compression schemes, including MPEG-4, MPEG-2, AAC and MP3. DVD-quality videos compressed with one of these schemes and stored in an MP4 file take up less hard drive space than the original, uncompressed video. Many portable media players and cell phones also support the MP4 format. You can change the video resolution of an MP4 file with video-conversion software to improve compatibility with portable devices.
Install the freeware program Any Video Converter (see Resources). Press the Windows "Start" button, select "All Programs" and then click the "Any Video Converter" program icon. Click "Add Video" and locate the MP4 file. Select "MP4 Movie" from the drop-down menu under Profile. Adjust the video resolution by selecting one of the preset values listed in the "Video Size" drop-down menu. Press the "Encode" button to change the video resolution.
Download the freeware video converter Handbrake (see Resources). Click the Windows "Start" menu, "All Programs" and then the "Handbrake" icon to open the program. Press the "Source" button in Handbrake's main menu. Click "Video File" and locate the MP4 file. Click the "Picture" tab in Handbrake's main menu. Adjust the values for "Width" and "Height" to configure the MP4 file's video resolution. Select "MP4 File" in the Container drop-down menu. Click "Start" to change the video resolution.
Use the freeware video transcoder MediaCoder (see Resources). Open MediaCoder by clicking the Windows "Start" menu and selecting it from the "All Programs" list. Click "Add File" and locate the MP4 file. Click the "Video" tab in MediaCoder's main menu. Select "MP4" from the Format drop-down menu. Click the "Picture" tab and then check "Resize." Select the new video resolution from the "Resize" drop-down menu. Press the "Start" button to change the video resolution.
Change the resolution to a size with the same aspect ratio as the original video. For example, reducing a 640-by-480 pixel video to 320-by-240 pixels will preserve the video's 4:3 aspect ratio. Changing the video to a resolution with a different aspect ratio distorts the picture.