I have spent ages trying to find the best way to save streaming files and clips on various sites, finally think I've found it, so hope this helps anyone with similar needs.
THE DEFINITIVE WAY?
Open Safari - if already open it helps if you close any windows/pages that are open, this makes finding the required file easier, if youre not adept at these things like me!
Go to the page you wish to download clip from. If clip does not automatically play, then click (or whatever site requires) to start playing of clip.
When link is playing/streaming open the Activity window (Safari-Window/Activity) find the relevant file, usually ending in mp3/mp4/flv/avi etc, it will be the largest file for that webpage (in YouTube the file you are looking for will have get_video in the URL).
Highlight and then copy the file address (Safari-Edit/Copy).
You can now close the Activity and Browser windows.
Open the Downloads window (Safari-Window/Downloads) and then use the paste command (Safari-Edit/Paste), Safari will automatically start to download the file. When the downloading is complete you can quit Safari, or leave open.
Click once on the icon for the file you have just downloaded, to highlight it. File is called get_video in the case of YouTube. This icon will be wherever you have set downloads to save to (Safari-Preferences/General).
Go to Get Info (Finder-File/Get Info). The Info window will open.
You need to adjust the Name & Extension details, so click in that box.
Files from YouTube are in Flash Video format, so they need to have .FLV at the end of the file name.
Other files may be .MP3 etc, check by clicking the arrow at side of More Info, then use whatever this is, at the end of your adjusted file name.
It is a good idea at this point to give the file whatever name you want, to make it easier to find later, just ensure it has the relevant extension at the end (eg tropicaldreaming.mpg).
If you already know the file type, you do not need to go to Get Info, you can just change the name that is with the icon.
You can sometimes change the extension and it will play in another format, for example from YouTube you could use a .MPG extension instead of .FLV and play it via a suitable player such as VLC (www.videolan.org/vlc).
If you have downloaded Perian (www.perian.org) you will be able to play the Flash video in Quicktime, just drag the clip icon onto the Quicktime icon, or open Quicktime and select to open the file in usual way.
Think the above probably covers most eventualities and is very simple to do, please comment with any experiences or relevant suggestions, or if there are circumstances where the above doesnt seem to work. I have used this for various downloads, including audio streams that can only be listened to online.
Some of the instructions might seem a bit simplistic/long-winded, but just wanted to make it easy for anyone to do, no matter their Mac experience.
So, precis of the above is:
Play Clip in Safari
Copy File URL from Activity
Paste File URL into Downloads
Adjust Name/Extension for File
Play - with assistance of Perian/VLC etc
Play Clip in Safari
Copy File URL from Activity
Paste File URL into Downloads
Adjust Name/Extension for File
Play - with assistance of Perian/VLC etc