Streaming Video Compression
Image Compression for Streaming Video

Once you have decided on a particular video format such as Windows Media, Apple Quicktime etc, you must decide how large the video file should be. The size of the file will affect the quality of the video and the transmission speed necessary to stream that file.

Streaming Video Compression

Since streaming video compression works by discarding parts of the video image, the more compression that is used the worse the end result will be. But compression significantly reduces file size, so a balance must be found that provides an adequate video image with a file size that permits your viewers to stream the file in real time.

Viewers who have faster Internet connections will be able to stream larger files, so you may wish to have a selection of files available for viewers to choose according to their connection speed. Generally speaking, a choice of three versions for each video should cover the range from dialup to high speed DSL connections.

Multiple Bit Rates - MBR

As an alternative to encoding individual video files, a single video file can contain Multiple Bit Rates or MBR so that the data stream can automatically adjust if there is network congestion. This type of file can only be hosted on a streaming video server as opposed to an HTTP server and there are some advantages as well as disadvantages to this method of video streaming.

One of the advantages to MBR is that the viewer is presented with a single view video button rather than having to make a choice depending on his or her connection speed. This makes the interface cleaner and less confusing. There is also the advantage that the video stream will not pause in the case of network congestion. The video stream will simply down shift to deliver a lower bit rate if the server detects a network slowdown.

On the other hand, there are several advantages to having your video available as individual files. The dimensions of the video image can change for each version so that small images can be used for dialup connections and larger images can be used for DSL connections. The audio track can also be customized for each individual file so that the audio quality increases with faster connections. Finally, this type of video file can be hosted on either a video streaming server or an HTTP server, so you have greater choice concerning the method of delivery.

The biggest factor determining the size of streaming video files is the amount of data that must be transmitted to view the video. This is measured as 'bit rate' with fast connections being able to transfer more bits per second than slow connections. A 56K dialup modem connects to the Internet at a speed of 56,000 bits per second whereas cable modems can download several million bits per second.

An important factor that affects bit rate is the dimension of the video image. Larger images have more pixels, and so require more bandwidth. Larger images also have more clarity, so it is usually appropriate to offer larger dimension video to viewers with high bandwidth Internet connections.

Another factor that affects bit rate is frame rate. A video file is made up of individual frames and the more frames per second the smoother the moving video image will be. Movies are usually filmed at 24 frames per second, and streaming video files need a similar frame rate to keep the image smooth. Video streaming frame rates are usually between 15 and 25 frames per second with the higher frame rates requiring more bandwidth.