Progressive
In a progressive download, content must be buffered (preloaded) to memory before a recipient can play it. The allowable length of any clip presented is limited to the hard disk space and RAM available on a user's machine. Progressive movies generally should not be made to last more than a few minutes. Content plays as soon as it is available, so on fast enough connections, progressive movies can appear to be streaming. However, if a user wants to jump ahead, he or she must download everything from the point currently in view to the point of interest.
Progressive downloads do have advantages. The goal of a progressive download is high quality at any connection speed. Given its superior quality, progressive video has proven very popular in the entertainment industry. It may take a lot longer for a user on a dial up modem connection to download the same clip as someone with a much faster dsl/cable/t1 connection, but once downloaded, the clip will have exactly the same quality.
Progressive downloads are sent using two different protocols, Hypertext Transfer Protocol (HTTP) and File Transmission Protocol (FTP). Both can be delivered using ordinary Web servers. Since progressive downloads use the same protocol as common Web content, there is less a chance of encountering problems getting past firewalls than with content from a streaming server. Progressive video can also take advantage of more advanced methods of compression than streaming video, such as Two-Pass Variable Bit Rate (VBR) encoding.
Streaming
Think of a streaming download as a "play-as-you-go" format. It is best suited for use in business presentations and online learning. Streaming is the only way to present live feeds and support broadcasts and multicasts (sending one stream to many viewers). A user's machine plays data as it is received and then discards it. Whether you're providing live broadcasts or video-on-demand (VOD) stored on a server, streaming allows broadcasts to run as long as is needed.
One of the primary goals of streaming video is to maintain real-time playback at various connection speeds. To make this possible, streaming media relies on different protocols and servers for delivery than standard Web pages. Real-time Protocol (RTP) and Real-time Streaming Protocol (RTSP) are known as connectionless protocols, in which speed is more highly valued than accuracy. Streaming servers reduce bandwidth overhead by broadcasting data across a network without verifying whether it is actually received.
Streaming software also allows you to adjust the data rate of your broadcast downward to meet your audience's capabilities. You can still reach audiences with lower bandwidth connections with some quality sacrificed.
B WORKS PRODUCTION GROUP produces both video web distribution formats.
Summary: if your
video is no more than approx. 2 minutes in length and does not need to
be live, select Progressive for quality and less cost because a streaming
server
is not
required.
If you require your video to be live, select Streaming.
Consider,
standard tv commercial spots run 20 - 30 seconds and are rarely
live.