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The End of the Trilogy: How to Solve Aspect Ratio Problems

The most common problems

Previously we have mentioned the most common problems connected with aspect ratio: when you play video on your DVD player it is stretched horizontally or vertically. Such problems can be easily solved hardwarily – by setting a DVD player or a TV set to the correct aspect ratio.

But what can you do if your video is shown incorrectly when being played in a software media player? For example, you have a video file that was converted before and for some reason it was converted with the wrong aspect ratio.

There is one more problem related to aspect ratio. Our users often ask how to remove black bars at the edges of the video.

With Need4 Video Converter you will easily convert your stretched video so that it becomes normal as well as remove unwanted black bars.

Classification of the problems

Let’s systematize all the problems associated with aspect ratio we have mentioned above:

1. The video has incorrect aspect ratio and is stretched
   1. vertically (all objects look narrow and prolonged);
   2. horizontally (all objects look flattened out).
2. The video has correct aspect ratio and is not stretched, but has black bars
   1. on the top and bottom;
   2. on the left and right.

Solution methods

1. Correcting stretched video.
   1. Most probably, a widescreen (16:9) video was stretched to the 4:3 aspect ratio, so that the original aspect ratio was broken. To correct this, we should stretch the video horizontally leaving the height of the video unchanged (see Pic. 1).
      
      Pic. 1: Stretching incorrectly converted video back to 16:9

      Knowing the height of the converted video, we need to calculate its width. Let’s denote the width of the video by W, and the height of the video by H.
      As the converted video is supposed to be 16:9, i.e. W:H = 16:9, the width can be calculated as follows:
      W=16×H:9.

   2. It looks like a 4:3 video was stretched to the 16:9 aspect ratio, so that the original aspect ratio was broken. To correct this, we should compress the video horizontally leaving the height of the video unchanged (see Pic. 2).
      
      Pic. 2: Stretching incorrectly converted video back to 4:3

      The converted video is supposed to be 4:3, i.e. W:H = 4:3, then the width can be calculated as follows:
      W=4×H:3.

2. Removing black bars.
   1. Most likely, a widescreen video (16:9) was converted to 4:3 using the Letter Box resize method. More information about resize methods here.
      The picture looks fine (not stretched), but black bars are added on the top and bottom of the video. This situation can be very unpleasant when you watch this video on your widescreen TV set, as it adds its own bars to the sides of the video to inscribe it to the screen. This is called windowboxing or postage stamp effect. Your video will look as in Pic. 3.
      
      Pic. 3: Windowboxing (postage stamp effect)

      You can remove the bars and return the video to the 16:9 aspect ratio using the Crop resize method. We need to crop the video vertically leaving the width of the video unchanged (see Pic. 4).
      

      Pic. 4: Cropping letterboxed video back to 16:9

      Since the converted video is supposed to be 16:9, i.e. W:H = 16:9, the height can be calculated as follows:
      H=9×W:16.

   2. It appears that a 4:3 video was converted to 16:9 using the Letter Box resize method. In this case black bars are added on the left and right of the video. You can remove them and return the video to the 4:3 aspect ratio using the Crop resize method.
      We need to crop the video horizontally leaving the height of the video unchanged (see Pic. 5).
      
      Pic. 5: Cropping letterboxed video back to 4:3

      The converted video is supposed to be 4:3, i.e. W:H = 4:3, so that the width can be calculated as follows:
      W=4×H:3.

Conversion instructions

To perform conversion of a problematic video file, follow these steps:

• add your video to Need4 Video Converter and select the necessary preset from the Output format drop-down list;
• click Settings under the Output format list;
• uncheck the Video same as input and Keep aspect ratio checkboxes;
• click the Options button in the Video stream area, select the target aspect ratio and click OK;
• specify the width and the height of the converted video that were calculated above;
• select from the Resize method list
  1. Stretch if you want to correct stretched video;
  2. Crop if you want to remove black bars from the edges of your video;
• click OK;
• convert your video.

If you still have problems or need detailed instructions on converting a certain video file, please contact our Support Team.

January 31st, 2011
Posted in Informative | 1 Comment »