Postby OttifantSir » 06 Dec 2009 23:44
AVI is by definition compressed. Or, to be more precise: The codecs available for use with the AVI-container is all compression-codecs. Off course, the person making the AVI-file can choose to set the quality bitrate so high as to inflate the size of the video, but that "doesn't happen". The whole point of video-containers and codecs is to get the size of the video down to a manageable size. "All" video and audio-codecs are the same. Even h.264/x264 or Theora or FLAC or Vorbis.
I don't remember the exact numbers, but I read about BBC and their Dirac-codec, and let's say (example, not real numbers) half an hour of raw footage, uncompressed, took about 20 GB. With the codec, it was compressed, with minimal loss of quality, to about 500 MB.
So you see, you WANT compressed video, unless you're working professionally with video.
There is no way to find, that I know of, how much a file has been compressed, because when it's compressed, it's a new file with its own information. Unless the maker of the file has included comments with the video about the original.
Typical compression on video:
DVD (8.5 GB) -> AVI 700 MB
BD (50 GB) -> MKV 720p 4.7 GB
BD (50 GB) -> MKV 1080p 8.5 GB
Off course, there are all kinds of sizes out there, but these are rather typical, as they are the sizes of CDs, DVDs and DL-DVDs since BD isn't too common yet.