Updated: October 4, 2007
Applies To: Windows Server 2008, Windows Server 2008 R2
Bit rate is the main concern when streaming digital media of any type. The bit rate affects both the range and number of people that will be able to experience your broadcast. In general terms, a low bit rate will allow you to reach the widest audience and permit the largest number of individual connections, but quality can suffer. Higher quality requires a higher bit rate, and the number of individual connections is limited. In addition, network connections between the encoder and the server should have an allocated amount of bandwidth that cannot be interrupted by other network traffic.
Remember that audio and video encoding of live content occurs in real-time with no opportunities to change settings after you have begun. You should practice your broadcast beforehand to determine the proper encoder settings.
Live audio broadcasts are typically a simple encoding scenario. There are several configurable components of an audio capture that can be adjusted during the encoding process to help you achieve the right balance of bit rate and audio quality.
Encoding video content is a much more complicated process. Video is simply a rapid display of a series of still pictures, called frames. Each frame must display a certain amount of detail, or resolution, to render the subject accurately. As the frame resolution is enhanced, more detail is shown. The number of frames displayed per second is known as the frame rate. As the frame rate increases, the motion in the video becomes smoother. The bit rate of the stream is determined by the combination of video frame rate and resolution. Both of these parameters can be modified during the encoding process to achieve the ideal bit rate for the user.
Over a high speed Internet connection or a LAN, smooth, high-resolution video is readily available. Extremely fast networks can render video and audio that can rival the quality of a DVD; however, over a dial-up connection, high-quality video becomes impossible without prohibitively long buffering times. There are techniques that you can use during the production of your live video content that will improve the audience experience regardless of the type of connection being used:
Keep movement to a minimum. Rather than send the entire picture of each frame in a video, streaming media only sends information corresponding to the differences from one frame to the next. If the differences are kept small, the bit rate can be kept low. Minimize movement of the subjects, the camera, and the backgrounds to reduce the amount of information that must be streamed.
Keep the production design simple. Wherever possible, reduce the complexity of the video images being streamed. Filming a subject against a plain background requires the transfer of less data than using a multicolored or irregular background. You can also sacrifice some sound quality for improved video quality in the encoding process, depending upon your priorities.
Make use of the intelligent streaming feature of Windows Media Services. You can set your encoder to encode your digital media at several different bit rates so that no matter what type of connection the user has, the Windows Media server always sends a stream that is optimized for that bit rate.
The system is less able to recover from streaming errors during a live broadcast because the content is only in the buffer memory of the server for a short amount of time. You can use forward error correction in Windows Media Services to provide error correction during playback without forcing the player to request error correction information from the server.