HD Compression Question

Discussion in 'AnyDVD HD (Blu-ray issues)' started by jackyl, Apr 2, 2007.

  1. jackyl

    jackyl Member

    I was wondering if anybody can answer this and also falls under the question of compressing HD content.From what i have read the typical HD and Blue-Ray are around 20 Gig which is considered 1080i.When i download a movie from the xbox live at 720p which is the same as 1080i and the movie is over 2 hours its only 7 gig.Is there a reason for the huge size difference such as a different compression and if its true 720p at 7 gig is it possible for us to crunch down the video to fit on a dvd-r dl?Just wondering if anybody had any ideas or am i missing something.
     
  2. colinhunt

    colinhunt Well-Known Member

    First off, HD/BD are 1080p. Secondly, 720p is not the same as 1080i; the latter's got more than twice the amount of pixels. That affects the file sizes on movies downloaded from Xbox Live. Also, movies on Live are compressed a bit more and the quality's not quite comparable to BD/HD.
     
  3. Peer

    Peer Redfox Development Team Staff Member

    You can't say "one hour of 1080i is xxxGB in size".
    Also 20GB is not "considered 1080i" - you probably read about HDTV there.

    Pretty much every HD/BD is 1080p - any other resolution is a very rare exception. You can control how much to crunch down a movie with 1080p - this could be 50GB or as much as 1 GB if you like (which would look terrible, but technically still have 1080p).

    HDTV from what I know, supports either 720p or 1080i. And yes - both resolutions result in apx. 1 million pixels per frame, but they are not really the same. I would expect 1080i to require significantly more (but far less than double) space, because of the higher "rate of change" between subsequent frames.
    And due to the limited bandwidth there do exist some recommendations to what max. datarate is to be used - my guess is that this is what you read about.

    And then still there is more to it: different codecs, among those MPEG2/4, AVC, ... not to forget sound compression lossless or not, ....
    This all has a lot of influence on the size of the resulting files and the quality of the picture/sound.

    So: sure, any BD/HD movie could be crunched down to any other size to fit on pretty much any other medium. The result will typically be less quality or maybe only less audio tracks or whatever.