Creating a Video Stream Step Two

Part of the video editing process discussed in the previous article involves optimizing the video to keep the video image as still as possible. Such a video is ideal for streaming to a variety of devices from hand-held PDA's (Personal Digital Assistant) to computers connected to broadband Internet.

The reason for this is that relatively motionless video images (such as talking heads) compress very well and therefore have a wider range of delivery options. The video dimensions can be kept small for PDA's and dialup, and made larger for broadband connections.

Therefore, the optimizing process starts at the video editing stage. Try to eliminate scenes that involve a lot of motion or perhaps crop the image so that background movement is minimized.

Alternatively, different versions of the same video can be made.

This allows you to optimize the video for various destinations: PDA's could receive a small-dimension video that is relatively static, while a larger dimension video with more motion could be prepared for broadband access.

Key Frames

Key frames are full-frame images that are spaced evenly throughout the video file. The frequency of key frames is the 'key frame rate' and may be expressed as every 'x' number of seconds or frames.

A key frame rate of every 3 seconds, for example, means that these full-frame images only occur once every three seconds. The in-between frames are computed by calculating how many pixels move and how they change.

A low key frame rate (such as once every 3 seconds) provides a high level of compression, and conversely a high key frame rate (such as one key frame for every 5 frames) results in lower level of compression and larger file sizes. Therefore key frame rate is an important consideration when optimizing your video file for streaming.

Videos with a lot of motion require a higher key frame rate, which in turn means that they are better suited for broadband connections. If your target audience is using dialup connections, a low key frame rate is needed, which in turn means that motion in the video must be minimized.

Encoding

Many video editing programs have built-in conversion functions which allow you to encode the video in a variety of streaming formats. All formats follow similar conventions, requiring you to choose several options that will affect the size and image quality of the streaming video.

Most encoding software has a number of templates that set the options for specific targets such as broadband Internet connections or video email. The templates are a good starting point and any of the settings can be overridden manually for the best results.

There are encoding options for video dimensions, audio quality, frame rate and key frame rate. There may also be a setting for image quality, with the higher settings (better quality image) resulting in larger files.

All of the settings, in fact, will affect the size and quality of the streaming video file.

There is always a trade-off – you can't get a full-screen action packed streaming video without ending up with a huge file, but conversely you can't reduce file size without losing image quality or reducing the dimensions of the video.

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