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I had a general question about streaming videos online; in particular, on YouTube. What really is required to smoothly stream videos at 360p or 480p? Then for that HD goodness, what really allows a computer to smoothly stream 720p and 1080p?

I'm not too sure whether it's to do with the CPU (speed, # cores, cache size), GPU (chipset, VRAM, memory type) or even HDD (IDE vs SATA).

What contributes to the ability to stream regular videos and, furthermore, high-definition videos online?

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Network bandwidth is the bottom line. If it isn't sufficient, your CPU, GPU and HDD won't make up for it. –  Mike Fitzpatrick Jun 3 '10 at 3:31
    
@Mike Fitzpatrick: what a nice answer that would be, instead it is a comment :) –  akira Jun 3 '10 at 3:36
    
@akira: Thanks. I was going to put it as an answer but I didn't know how much bandwidth is required for the various formats so I thought best to simply comment. I see you and @Josh K have provided that, so thank you both :) –  Mike Fitzpatrick Jun 3 '10 at 3:46

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up vote 2 down vote accepted

Number one contributer would be your available bandwidth.

The more you have the better it's going to stream. That's not to say it's impossible to stream at lower bandwidths. At the lower bandwidths stuff like latency and dropped packets come into effect, in essence the quality of the bandwidth is also important. See Pingtest.net.

That's simply getting the video to your computer. For 360p you'll need at minimum about 3Mb for smooth streaming. 480p you'll want about 5Mb. I honestly don't see a point in streaming 720p or 1080p on a residential line.

If (and I'm guessing you are) using a Flash based player, it's going to burn a lot of CPU cycles. Depending on the browser it could also hoard RAM. I'm not sure if a decent or higher end GPU would help, and a HDD would probably be a non-issue unless you're caching to disk.

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i was about to send "mostly: bandwidth.", you beat me by seconds :) i would add something like example bitrates to illustrate the effect, eg: you have 3-7mbit/s for dvd-content .. you would need that much in terms of downstream bandwidth as well. –  akira Jun 3 '10 at 3:28
    
@akira: You have the rep, edit it in! ;) I'll do it, hand on a sec. –  Josh K Jun 3 '10 at 3:32
    
@Josh K: a good comment gives me even more rep, an edited answer of someone else ... what? :) –  akira Jun 3 '10 at 3:35
    
@akira: I don't believe you can gain rep from comments. You get a warm fuzzy feeling knowing "you dun well." ;) –  Josh K Jun 3 '10 at 3:36
    
@Josh K: there is the "great comment" badge which is smiling at me right now ... but we get offtopic here :) –  akira Jun 3 '10 at 3:42

First, you have to get the video to your computer. This involves bandwidth between your computer and the server. The required amount of bandwidth depends on how the video is encoded and the quality of the video - HD content requires more bandwidth. This the culprit problems more often than not.

Second, your computer has to be able to decode and play back the video, which requires CPU and Memory. Many recent video cards can take over this task, significantly reducing the amount of CPU time required to decode the video. Higher definition content has higher requirements.

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