Understanding Bits and Bytes

Before you can begin streaming audio or video, you must do a little math.

Computer 101

In computer speak, files are measured in bytes. Generally, audio and video files tend to be large.

When you connect to the Internet with your computer, you do so at a given speed. The speed is measured in bits, not bytes. For example, a modem connection can try for 56 kilobits per second but usually falls short of that (near or less than 46 Kbps). A connection through your cable company can be as fast as 3.5 megabits per second (Mbps), although most such connections top out at 1 Mbps.

Video being streamed from your server must be properly prepared so users from all types of connections, from slow (modem) to fast (cable or better), can see it properly.

If you want to stream a 10 MB file to a user with a 1 Mbps connection, about how long will it take (Table 12.1)? It will take about 1.4 minutes for a 10 MB file to be downloaded from your server to a computer over the Internet using a 1 Mbps connection. Imagine how long it would take over a modem connection!

Table 12.1. Bits and Bytes

FILE TYPE	SIZE	MATH	RESULT
Megabytes	10	Multiply by 1024	10240
Kilobytes	10240	Multiply by 1024	10485760
Bytes	10485760	Multiply by 8	83886080
Bits	83886080	Divide by 1000	83886.08
Kilobits	83886.08	Divide by 1000	83.88608
Megabits	83.88608	Divide by 60	1.39

Next, you must ask how fast your connection to the network is. If you do some more math, you can figure that if 11 people, each with a 1 Mbps connection, all download the same file at the same time, the total bandwidth your server must contend with is near 923 Mbps (10 MB file x 11 users)! Most newer Macintosh computers contain Ethernet cards that can transfer data at 1 gigabit per second (Gbps). You can see that 1000 megabits (1 gigabit) minus 923 Mb is 67 Mb. The 11 people have almost saturated a gigabit Ethernet connection, and it isn't likely that you have a gigabit connection from your server to the Internet.

This example illustrates the problem often faced by administrators using QTSS: quality versus quantity. You want a nice clear video that isn't the size of a postage stamp, and you want several people to view it at the same time. You should now realize that doing this has serious implications on your bandwidth.

Tip

• One note of caution: You should only stream content that you own. Streaming content that is copyrighted will probably violate copyright rules. Respect the rights of the owners of audio and video copyrighted material.

Hinting files for streaming

This section briefly discusses the process of hinting, which allows a video file to be prepared to be streamed over a network. For example, a video may be encoded at three different speeds: one for modem connections, one for cable and DSL, and one for local Ethernet (LAN) connections. When this is done, three separate files of the same video exist. QTSS can present a single file to the person connecting, and that person's QuickTime Connection Speed settings determine which file they will receive (Figure 12.1). Hinting is basically the addition of an extra track that allows this to happen.

Figure 12.1. You set the QuickTime connection speed the same way on both Mac OS X Client and Mac OS X Server.

You can hint with a tool available from Apple called MakeRefMovie; you can also do it with iMovie. MakeRefMovie is a bit more involved.

To hint an iMovie file:

1.	Open iMovie on any Mac OS X Client. It's generally located in the /Applications directory, but you as the administrator of your Mac OS X Client computer could have moved it anywhere on your system.
2.	Open your last iMovie project, and choose File > Share (Figure 12.2). Figure 12.2. Choosing File > Share is the first step to hinting a movie. The Share dialog appears.
3.	Click the QuickTime button, and choose Web Streaming from the Compress pop-up menu (Figure 12.3). Figure 12.3. Clicking the QuickTime button and selecting the compression for Web Streaming prepares the iMovie for streaming. Once you save the file, it's automatically hinted (that is, the hint track is added) for use with the QTSS. Chances are, however, that you'll be responsible for streaming the content, not creating it.

Tip

• You can also use QuickTime Player Pro to export a movie as a hinted movie.