A widespread and versatile video container, the MP4 file is a popular file type for video information. It is fully compatible with many codecs and a host of software applications. However, though it lends itself easily to common use and is often easy to troubleshoot, MP4s can suffer from an issue with black frames.

Aspect Ratio and Resizing

An aspect ratio represents the general size or dimensions that a given video file will display in a video player. In MP4 and other digital video files, the aspect ratio is typically represented as a pixel dimension, such as 1280 by 720, much like a screen's display resolution. This results in a black outline around the video that fills in unused space in the player's screen. Most video players provide an option that allows you to resize a video to fit on the screen, thereby removing the black frames. If you're using Windows Media Player 12, open the program, select the "View" menu, and then choose the "Fit Player to Video" command. Keep in mind, however, that in some video players this may result in a deformed final image, especially if you're trying to view a widescreen MP4 file on a non-widescreen display.

Cropping

Many video-editing programs, both free and professional, offer editing features for cropping and trimming your MP4 file, thereby freeing it of its black frames. If the black border around the video transferred directly into the video from original material and exists as a part of the data, then you can crop it out with ease. If your video has no native black border around the video information and you're simply having trouble making it display correctly, however, then you have to proceed with more caution. Assuming the problem lies with improper display equipment and therefore merely an inconvenient aspect ratio, consider your options before proceeding, as you will need to permanently edit out pieces of the original file in these cases.

Re-Encoding

If you own the original content and the video, you need only to reopen your original video-editing software and re-encode the video in question to a more agreeable aspect ratio. Assuming you still possess the original files, you can recreate a new video that's custom-tailored to fit your display equipment. If you need to crop your original video, you can fix the original sizing errors that led to the creation of the black frames in your finished product before re-encoding.

Troubleshooting

When uploaded for use online, improper height and width frame measurements in coding can lead to odd displays. Data can also become corrupted or damaged. Pieces of data can disappear, leaving you with distorted MP4 files and entire seconds or more of video missing. In these cases, re-encoding your MP4 file to rid it of these black frames or backing up from a saved, original file may be your last recourses in the event of damaged or lost data.