Frame Grab Tutorial

Tech Note for Nerds

Motion video began appearing on the Web soon after the first image-oriented browser (Mosaic) was released in 1993, but there was a problem. Video files were huge and users had to wait for the entire file to download to their computers before they could view them. Then, in the late 1990s, Real Networks and others pioneered a process by which video would start playing much more quickly. Once enough data downloaded to create a video image, it would pop up on a user's computer.

This new technology was called "streaming" video.

Apple was slow to develop streaming for QuickTime. And they've implemented it in a confusing manner. For Apple, there are two forms of streaming: (1) "fast start" downloads through a regular Web server (HTTP) and (2) "real" streaming through a streaming server (RTP/RTSP).

Since fast-start video can be done on any Web server and effectively streams video to users soon after it's invoked, it's a great way to present video online. But, to Apple, it's not really streaming. For Apple, streaming is only really streaming if you buy an expensive streaming server from them.

Fast Start Vs. Streaming, According to Apple

When deciding on the best way to deliver your QuickTime movies over the web, which should you choose--Fast Start (HTTP/FTP delivery) or streaming (RTP/RTSP delivery)? For live feeds that must be transmitted in real time, streaming is the only answer, but for other types of movies, each delivery method has its pros and cons.

Why Choose?
Because this is QuickTime, you don’t face a hard-and-fast choice. You can offer more than one option to your audience.

For example, you can create a fast-start movie for viewers with slower connections and a streaming movie for viewers with faster connections, and offer both of them from the same web page. More on creating reference movies.

Or you can embed streaming tracks within a Fast Start movie. When the Fast Start movie is sent over HTTP, it will call the streaming tracks from the streaming server. This can happen even while the Fast Start movie is still downloading. Use this technique to mix things that must stream, such as live feeds, with things that can’t stream, such as sprites.

Fast Start pros

• No special server software needed

•Movie gets through no matter how slow the connection

•With fast connection, movie plays as it downloads--it looks like streaming to the audience

•Delivers all types of QuickTime media, including sprites and QuickTime VR

•Lost packets are retransmitted until they are received

•No problems with firewalls or NAT

Fast Start cons

• Can’t broadcast or multicast

•Can’t transmit live feeds

•Can’t skip ahead; audience must download the entire movie

•Puts a copy of the movie on the local hard disk--you lose control

Streaming pros

• Only way to transmit live feeds

•Broadcasts and multicasts (one stream to many viewers)

•Random access within prerecorded movies

•Uses no space on viewer’s hard disk

•Never uses more bandwidth than it needs.

•Doesn’t leave a copy of the movie on the viewer’s hard disk

•Can stream individual tracks into a movie from any streaming server anywhere

Streaming cons

• Requires a streaming server and/or broadcaster

•Movie breaks up if data rate exceeds connection speed

•Lost packets are gone for good; movie always loses some data (though some data is almost always lost over the Internet – over a LAN, there is normally no data loss)§.

•Some QuickTime media types, such as QuickTime VR, Flash and sprites, don’t stream.

•Can be stopped by firewalls or NAT

F i n e P r i n t
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