References
 | Streaming World... http://www.streamingmediaworld.com/ |
| Real Audio... http://www.realaudio.com |
Basic Concepts for Streaming Media
The basic point of streaming media is that it is downloaded and played at the same time.
Adapted from Microsoft and other sources...
Basic steps...
- Capture
- Convert
- Distribute
- Play
Capture and Convert: The first thing you do is capture the movie to a file on your computer. This process is called digitizing or capturing. You convert your analog audio and video to a digital form that can be saved as a file.
Distribute: With your movie digitized to a file on your computer, you can distribute it just as you would any other data (e.g., floppy disks, CD-ROMs, or other storage media). You can also distribute the data over a network, such as the Internet.
Digital media can be delivered to clients over a network using one of two methods:
- Downloading: the complete file is downloaded for playing
- Streaming: data is downloaded and played as enough is available for presentation.
Play: The final step is accessing and then converting the bits—the digital instructions—back to analog form so the movie can be viewed. A digital media file can be opened and played directly if it is on the end user's computer or another computer connected through a LAN (Local Area Network). An end user can also play Windows Media files by streaming them from a streaming file server.
There are three main ways to incorporate streaming media in web design.
- Open a "player" and the downloaded file on the client machine (e.g., Windows Media Player)
- Via object tags in a browser (plug-ins or ActiveX)
- Built-in browser technology (RealPlayer, Windows Media Player)
Streaming: Play the data as it is being received by your computer. Instead of waiting for the bits to be copied, they would be converted and played as soon as they arrive. The bits are played as they are being received from a server on a network and are usually not saved on your hard disk drive.
Streaming also enables you to do live broadcasting, just like a radio or television station, except over the Internet. You can eliminate the need for files altogether.
For streaming to work, the bit rate of the media must be lower than the bandwidth of the network. Bit rate is the speed at which data is sent across the network. Because you are playing the digital media as it is being received, if the network bandwidth is lower than the bit rate of the media, the media will not play properly.
If you download a still image over a slow connection, the image quality will not be affected. It will just take longer for all the bits to get to your computer. The still image itself does not have a bit rate. On the other hand, streaming media does have a bit rate.
As long as the content is playing, the bits are streaming at a steady and continuous rate. The player must receive a stream of bits continuously or the picture and sound will either stop or will play back unevenly.
Another way to look at it: when you encode a file for downloading, file size is important and bit rate is irrelevant. When you encode a file for streaming, file size is irrelevant and bit rate is important. You can easily stream a very large file, even one that has an undetermined size (such as a live stream), as long as the bit rate is within a client's bandwidth.
Compressing: The bit rate of high-resolution, full-frame, broadcast video is about 128 megabits per second (Mbps). To download one second of broadcast video over a 28.8 kilobit per second (Kbps) connection using a modem would take one hour and 14 minutes. Streaming this type of video would be impossible over a network. To recreate every detail of a video frame would require so many instructions that most computers couldn't even play the video. It would also require a huge amount of storage space for the file. Streaming media handles this problem by using compression. Compression lowers the bit rate while maintaining the best possible quality.
A compression algorithm analyzes the data and removes or changes bits so that the integrity of the original content is maintained as much as possible, while reducing the file size and bit rate.
An example of a Windows streaming media file is ...
| aubreyclip.asf |
| The file is 26KB (compare to the 600KB file on the video page) |