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Video Streaming Need To Know: Part 2 - The Real World


In Part 1, I was surprised at how little packet loss it took to affect video streaming, but was just as surprised at how hard it was to disturb files played using TCP/IP based protocols. Armed with this knowledge, I set out to see whether success in wireless video streaming was really as hard as I have been making it out to be.

We found in Part 1 that video streams can vary widely in their bandwidth needs and that there are two methods for playing video files across a network. Since I mainly wanted to explore the largest uncontrollable factor in wireless streaming - neighboring WLANs - I decided to use one test file and one play method. I chose an uncompressed VOB (MPEG2) test file with a bandwidth profile shown in Figure 1. The bandwidth was measured using Hoo Technologies' Net Meter.

Figure 1: Test file bandwidth profile

The four-minute test file has plenty of action in it, which accounts for the fairly high average bandwidth. These figures are above the 5 Mbps or so bandwidth number that I've heard thrown around in IPTV-related discussions with equipment vendors, but aren't out of the question for downloaded or ripped content. For comparison, Figure 2 shows the bandwidth profile of a short HD movie trailer.

Figure 2: Quicktime HD 720p file bandwidth profile

Note that this is a 720p file in Quicktime HD, which uses the very bandwidth-efficient H.264 codec. While the average bandwidth (the one that most vendors will quote, of course) of the HD file is lower than the test file's, the peaks are more than 3 times higher.

I chose UDP streaming as the play method because it is the most likely to be used by both network-based content providers and for in-home network play of downloaded and stored content by devices using UPnP AV and DLNA protocols.

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