4. Bit Rates And Encoding

There are actually two ways to play remotely located multimedia files. If you're using a PC or other device that is capable of navigating local and networked file systems, you can simply navigate to the folder / directory where the desired file is stored using your media player application. When you open the file, it will then be played using whatever networked file system protocol is used by your operating system. For most popular operating systems, this would be some form of SMB (Server Message Block), run on top of TCP/IP.

The other way to play remote multimedia content is to run a media server that uses a streaming protocol to deliver content from server to player. These servers use protocols such as RTP and RTCP that are built on the UDP protocol.

The conventional wisdom on these two protocols is that TCP/IP is more robust than UDP because TCP incorporates mechanisms to ensure that data arrives in order and error free. But TCP is supposed to be ill-suited for multimedia distribution due to its larger overhead and focus on getting data to where it is going without errors, at the expense of timely delivery.

UDP on the other hand has much less overhead than TCP, so it is better suited for real-time applications like streaming where on-time delivery of data is more important than reliability. It's up to the data receiver to fill in the gaps when data doesn't arrive or gets corrupted in transit.

My first step was to test the "conventional wisdom" by viewing three different video test files using the file play and streaming methods. The files used both different codecs and bit rates, so that I could see if those factors affected their susceptibility to data transmission errors.

High bit rate: Ripped DVD VOB file, MPEG 2 codec Medium bit rate: DivX movie trailer file using DX50 codec, 640x300 resolution and 24 fps frame rate Low bit rate: PSP movie promotion feature using avc1 (MPEG 4) codec, 368x208 resolution and 30 fps frame rate

I used the VideoLAN VLC Media player 0.8.5 to both play and stream the files. I chose VLC because it could handle all of the above file types and either open the file directly for playing or receive it streamed from another VLC player acting as a streaming server. Streaming was done using the VLC UDP stream option defaults and no transcoding.

As anyone who has experimented with multimedia codecs knows, file bit rates have a significant effect on playback quality and are also a key factor in determining your success in networked video viewing. But a file's bit rate can be difficult to get a handle on simply because the information isn't often part of the file's metadata or properties. And even when it is included, the single value shown isn't that helpful because bit rate constantly changes.

To see the actual bit rates of a file being played you need a tool that measures the speed of the bits actually flowing through your network adapter. After trying a few, I ended up using Hoo Technologies' Net Meter. It does just about everything you'd want from a bandwidth meter (except I'd really like a button to clear the plot without having to restart the program). It runs on Win 98, ME, NT, 2000 and XP and is free to try for 30 days and $20 to buy.