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[This post is taking part in our Designing Hardware for HD series. Be sure to check it out!]

Last week I tried to cover the video inputs and outputs, which are necessary in videophone design. This time I want to talk about what types of video feeds you would want to see on your monitor(s) and how they would be displayed.

The Basics

Let’s start with the basics. I’ll assume you have a monitor that supports 720p resolution for the video, and that the only two video feeds in the system are the one coming from your own camera (local) and the one coming from the remote terminal (remote).

Basic video feeds to/from a videophone

Full Screen

In the case of a full screen layout, the easiest thing to do would be to show on the display the video coming from the remote terminal (over the Ethernet):

Remote video shown in a full screen layout

R here will denote the fact that we are viewing the video feed from the remote terminal. In this example, it takes the full screen.

There are, however, two additional “complications” you should take care of: The incoming video might be in a different resolution than what you want to display; To this you may add a possible aspect ratio issue – for example, the monitor is 16:9, the incoming video is 4:3.

What do we do in such cases? We scale:

• We might need to downscale a video feed – especially if we want to place it in a smaller window on the screen (for instance, a 1080p input displayed in a 720p full screen layout).
• We might need to upscale a video feed – when working with limited available bandwidth on the network or when communicating with non-HD terminals (for instance, a 480p input displayed in a 720p full screen layout).
• If we have a smaller video feed than the resolution we display, we might want to just center our video feed inside a bigger frame (and not scale at all). Although some may consider it, well, ugly, but upscaling takes a lot of processing power and may distort the image (if the ratio between the input and output is big).

Dealing with aspect ratio differences is a bit different – in such cases we can either scale to fit or scale and crop:

In the example above a 4CIF (704×576) resolution input is to be displayed on a 720p full screen layout. On the left, the input is centered but not scaled. In the center, the input is scaled to fit, which means it is scaled up until one of the dimensions fits the output resolution. On the right, the input is scaled and cropped, which means it is scaled up and then cropped to fully fit the output resolution.

Cropping should be left as a non-recommended last resort, as this may lead to valuable information missing from the displayed image. As most people use their self view (coming directly from the camera) to position themselves, and as the remote side will not see the same image as the self view, this can lead so some awkward results.

Some notes:

• While I won’t be going over these options and scaling in general in this post, it’s a requirement for most of the use-case scenarios a videophone has to handle.
• Scaling affects the image quality, so take that into consideration in your system requirements.
• You could use the same single full screen view window for showing the self view image from the camera or for any additional video feed that you have to display.

PIP

Next in line, is the notorious PIP (Picture-in-picture) layout.

Typical PIP layout

In this layout, the remote view will usually take the full screen area, while the self view from the camera will be shrunk down and placed in one of the corners of the screen.

PIP locations on the screen

An additional option, that is usually available in most videophones, is changing the size of the PIP window:

PIP in different sizes

Again, the choice of which feeds to show where in this layout is up to your application’s needs and the use cases you will be designing later for your end users. But you should take them into consideration at this stage – they might affect how you pass video through your system.

Side-by-side

Another possible layout for two video feeds is the side-by-side one:

Classic side-by-side video layout

Here, there might be variations in the sizes of the windows as well:

Different side-by-side based layouts

What’s Next?

In a lot of videophones these are the layouts that are supported. But what happens when there are additional video feeds? How will that change the picture? I’ll try to answer it in my next post, where I will analyze the layouts necessary in a videophone room system supporting PC sharing (aka dual video).