Putting Sound and Video into Web Pages

Real-Time vs Download-Then-Play

To play in "Real-Time" refers to either seeing/hearing the movie/sound as it happens or as it plays back from the server. For example, real-time sound could be tuning into a radio station and hearing the live broadcast as if I was listening to it on the radio. It could also be going to a music site and clicking on a music track and imediately hearing it, as if I put it into my CD player.
This approach does not require any hard disk space, as what comes in goes directly out the screen/speaker.
There is no easy rewinding or fast forwarding of the stream.

Real-Time Video is out of the question for the majority of users for the near future.
For example, one minute of RAW video matching TV quality would take about 12 hours to download with a 28,800 modem. If my math is correct, it would take a 20Mbps modem to do this, not may people have these.
With the best video compress using hardware, it would still require a 1.5Mbps connection to provide real-time video.

Real-Time Audio is available now and does work fairly well over 28,800 bps modems.
The most common method is via a package/standard called RealAudio.
To attempt to keep the sound smoothly flowing, real-time packages buffer a few seconds of sound at the start, and then play back with a slight timing delay.

In this approach, the file is downloaded to the users harddisk and then played back.
The viewer can easily rewind or fast forward through the clip.
Currently really the only way to deal with video, and quite good for audio.

This is basically the Download-Then-Play, except that the player allows you to play what you have received to date.
If the connection speed is fast enough, this can appear to be real-time playback.
Very useful to the user, as they can view the start of the file and decide whether to continue the download.