Firstly, there is no difference between streaming and downloading. All those who say they are different are crazy.
Downloading: Downloading means when you are actively downloading or capturing a file. In downloading, one cannot be sure of the content of the video or audio. But, he can pause and resume the downloads whenever he wants. Particularly, when you download the file it is stored permanently on your computer hard drive where you can later edit or delete the file.
Streaming: Streaming is mainly what we say buffering a video file. This is VERY SIMILAR to downloading. When a person is buffering or streaming a video or audio file, he or she is actually downloading the file. The only thing is most people don't know that. The file which is downloaded is mainly a temporary file and is primarily stored in the computers cache. Hence, every time we refresh the page, we have to buffer the file again because it is actually downloading into cache.
Best Solution: If your are on a computer, then goto the internet's explorers options. Open the temporary files tab or cache option.( Do this only after you have streamed the video completely once.) Keep scrolling through the list unless you find a file which is very big which you can say is a video file. Right click it and save it on the computer with a particular name. Open it with VLC and ta-da......you have downloaded the streamed file without needing to actually download it. i.e you have downloaded the video after watching it.
This method will cut your internet usage by half if you are watching videos or listening songs.
ONE MORE THING: You are downloading DATA even when you are streaming a video. So don't wonder why your internet usage is high.