On Youtube or any of the others if you are getting a buffering message then the problem is with your computers connection to the internet.
Now this may be due to the speed of your ISP, or a problem with your router.
Without knowing more about your ISP and network configuration it would be hard to put the finger on who is to blame.
If you live in a rural area and are still using a copper wire connection instead of either fibre to the cabinet (FTTC) or fibre to the home (FTTH) the problem is most certainly going to be your ISP just can't give you anywhere near enough speed. I live in a rural area and face the same problem and at times it's a pain in the backside because even trying to listen to music on Grooveshark can be troublesome.
Do you know what speed your ISP claims to give you - some ISP's will say we will give you "upto 20mbps" but if you ask them properly they will then say well the maximum your line can support is 2mbps. If your in the UK Ofcom have tried to stop this by forcing companies to tell people exactly what speed they are likely to achieve before signing a contract. Remember if they say "upto" then that is not the real speed, and if you ask them to do a line check they should be able to tell you the real speed you can acheive.
Now if your getting buffering issues I'm going to assume that you are either on ADSL (copper wire broadband), or there is an issue with your router.
If your on ADSL there are a few more things that can slow your internet down and that can be controlled by you.
At some point your router or modem goes into the phone socket. Do you know which phone socket it goes into. If you have more than one phone socket in your house try and ensure that your router or modem is plugged into the master socket. This is the one that is connected directly to the outside, and not an extension as extension cable is nowhere near as good as the copper wire outside and can severely affect speeds.
In addition to this ensure that you have a filter on the socket, and also place a filter on every other phone socket in your house. An ADSL filter is a little white box, with two sockets one labelled DSL and the other labelled Phone (or symbols to indicate the two). The way ADSL broadband works is that it sends the internet signal on a high frequency, this reduces the amount of frequency available for talking on the phone, but on a phone system your hardly going to be using it for sending down high quality audio so as long as you can hear the person at the other end the slight loss of quality really doesn't matter, plus the frequency that is used is usually higher than what some people can hear anyway. Now the filter is just a simple low-pass audio filter. It removes any high frequency sounds that may interfere with the internet connection. It also removes the high frequency internet noise from your conversation as well, which is why if your filter isn't working properly, or you forgot to install one you can sometimes hear high pitched noises over the top of your conversations on the phone, what you are hearing is the internet and as annoying as it is for you it is worse for the computer, because you know you can ignore those tones, where as the computer can't determine what is tone and what is speech. Not putting filters in will severely reduce your internet speed, and ensure you put a filter in on every phone, because normally on extensions if they're wired inside the master socket they'll be wired so that they're after the filter which is why an additional filter is required.
Ok so we've done that - router/modem plugged into master socket, and filters fitted to all phone sockets.
Now what else could be causing slow internet...
Internet sharing - This is one that is getting more and more of a problem with the increase in devices that use the internet. You have both internal and external sharing. External sharing there is very little you can do anything about, unless you look for an ISP with a low contention ratio e.g. a contention ratio of 50:1 means 50 people are all connected to that original connection so that speed has to be dished out to 49 other homes as well as yours, where as a contention ratio of 20:1 means only 20 people are sharing your connection (nb. if your speed is 2mbps and your on a 20:1 line you'll probably find that the start of the line has a speed of about 20mbps based on the fact that they assume about half the people wont be using the internet all at the same time except at peak times when you may notice the internet slow down to 1mbps). Of course other than choosing an ISP with a low contention ratio or moving house to a place with very few properties there is little you can do about the external sharing.
On top of that you have internal sharing, remember that at the box on the wall the internet may come in at say for example 6mbps, but then it again is split between numerous devices, you may have a PS3, Xbox 360, PC, Laptop, Tablet, Smartphone all connected and each of these are going to try and grab a bit of that 6mbps which means that if shared equally each device is left with only 1mbps to play with, of course it doesn't exactly work like that, each device can be given different amounts of internet speed depending on how much it's demanding that speed. so one PC that has a torrent program running might be taking 4mbps leaving just 2mbps to be shared between the other 5 devices.
Then as well as all the above if your on a wireless network this can also slow the connection down. Depending on whether your using 802.11B, G or N. 802.11N will give you the best speed and best connection between your router and your PC apart from changing to Ethernet cabling. But all radio frequencies can have various amounts of interference due to other devices producing EMF (electro-magnetic fields). An EMF is an invisible magnetic field that surrounds all electrical devices, and this can interfere with other devices. Sometimes you may be able to pinpoint the exact thing that is causing you problems but quite often it can be either a number of things all combined, or totally unexplainable. I know in our house we have a immersion heater due to not being on gas, and at night when that turns on it can severely weaken the internet signal, but also we sometimes get some radio interference from the radar station that is on the hill near us. So that can also affect your speeds and cause buffering
Then finally it can be down to what you have running in the background of your PC whilst trying to watch the video. If you have something like uTorrent running in the background downloading loads of files, whilst trying to watch a video, or if your PC has a virus, adware or spyware, all these can be borrowing your bandwidth and slowing your internet down and causing video buffering.
So there are a few checks to find out if the fault is internally.
Firstly quit all the extra programs that you have running - ensuring they do quit and don't just sit in the taskbar near the clock - right click on any that do that in the task bar and select quit from there, or an even better way is to download a linux live CD like puppy linux (http://www.puppylinux.org) boot from that and see if the buffering happens with that (bear in mind that you'll need it to connect to the network, and possibly install flash to play a video). If it does then you know the problem isn't with any programs you have running.
Next thing to try is to turn off all other devices where possible that are also connected to your internet - this includes smartphones, smart-tvs, games consoles, blu-ray players, etc. and see if that makes a difference. If it does then you have too many devices on your internet.
And finally if possible move your PC to the router and connect directly with ethernet to the router. If you still get buffering at this stage, then the problem is most likely to be on your ISP's side and other than change your ISP to a better one there is very little you can do about that.
One other thing I forgot to mention above is to try and reduce the video quality.
sometimes Youtube will assume your internet connection can handle 720p resolution, if you click the cog on the bottom it brings up a list of resolutions, try 240p or 320p, the video may not look as good, but it shouldn't buffer as much, plus pause the video for a few minutes before starting to play it to give it chance to buffer a bit, you can see the buffer location in the bottom it's the bit where the play bar has gone from black to grey.
Note: This post was edited by its original author to merge two posts into one. on 08/31/2012 at 11:08 AM PT