For more sources see www.newfreemoviedownloads.info . This compression is necessary in order to reduce the movie file size which otherwise would occupy too much space and copying it or transferring it from one device to another would be a complicated step to achieve.If you wish to watch your AVI movie in your PC and this movie was compressed with a particular codec, you will need to have the same codec installed on that PC. For me size matters, the larger I can print an image the better.