Lets start with container files. I think these are fairly easy to get your head around (codecs are a bit more complex in my opinion).
Container File
A container file is a single file that has more than one file type in it. Zip files (if you know about them) are a good way of remembering this; you can zip up a load of files into one single (zip) file, as shown below. This is a convenient way to send loads of files at once to someone else (it also allows compression but we are not interested in that at the mo).

Codec
Depending on where you look codec stands for Compress/Decompress or Code/Decode. (For the Higher Computing exam consider it to stand for both!). It does what it says on the tin, it encodes a multimedia file in some format (there are lots of different codecs) and then decodes it at the other end (when you play it).
Streaming
While I remember I don’t think I put this on a blog post (even though I think you are all pretty clear on what streaming is!). Streaming is the viewing of (or listening to) multimedia data while it downloads. It is what we do all the time on video website such as youtube and increasingly on excellent multimedia applications such as the bbc’s iplayer (where you can stream tv from the last week).

Powerpoint Notes for Container Files / Codecs: