In the third of this series of articles, discussing the problems of uploading screencasts to free video hosting services such as YouTube and Metacafe, we will take a look at the effect of the aspect ratio of the screencast.

The aspect ratio of a screencast refers to the ratio of the pixels making up the width of, to the pixels making up the height of the screencast.

As mentioned in the previous article in this series, the maximum size of a screencast that can be uploaded to YouTube is 320 pixels in width, by 240 pixels in height. In terms of the aspect ratio, for each 4 horizontal pixels, there are 3 vertical pixels, giving an aspect ratio of 4:3.

Now suppose the aspect ratio of your screencast does not match the 4:3 ratio specified by YouTube in order to successfully upload screencasts to their site. In this case, YouTube automatically resizes your screencast so that it fits within the 320 x 240 pixel dimension required.

During the process of resizing process, in order to make the screencast fit, pixels that were previously square, are either stretched where the screencast dimension is less than required, or squashed where the screencast dimension is greater. This leads to warped video frames, severely reducing the quality of the uploaded screencast.

Consider the following example, where we are trying to upload a screencast with dimension 240 pixels in width, and 320 pixels in height, and where the pixels are initially square.

Now consider uploading the screencast to YouTube, hence it needs to be resized to 320 pixels in width, and 240 pixels in height.

Let's first of all discuss the width of the actual screencast in relation to the required width. In this example, we have to stretch 240 pixels so that it fits in the space normally occupied by 320 pixels. Because of this, each pixel must be elongated along the x-axis by a factor of 1.33.

Similarly with the height, we have to squash the pixels so that 320 pixels fits into the space usually occupied by 240 pixels. This means that in the y-axis, pixels will be displayed with height 0.66 of their original height.

Below is an example of the effect of altering the aspect ratio. The first image shows a frame of the original screencast, which to clearly highlight the effect on altering the aspect ratio, has dimension 240 pixels by 320 pixels.

The second image shows the result of resizing the screencast so that the aspect ratio is 4:3, and fits with the requirement of uploading screencasts to YouTube.

As you can see, the resize of the image severely effects the image quality, reducing the overall viewing quality of the watcher, and as a result the learning effect of your screencast

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·  Screencasts, YouTube and Metacafe - The Problems Exposed Part 2 - Video Resolution ·  Screencasts, YouTube and Metacafe - The Problems Exposed Part 1