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can dvd movie files be compressed like you can with audio (wav to mp3s)

Discussion in 'MPEG-1 and MPEG-2 encoding (AVI to DVD)' started by sunofsan, Apr 17, 2005.

  1. sunofsan

    sunofsan Member

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    Was wondering if dvd movies can be compressed into much smaller files which could be downloaded rather quuickly then converted back to dvd files, just like you can with wav files to mp3 with audio. Is that what mpeg files are? How does avi fit into this? Would there be a drop in quality between the original movie file and the resulting movie file after the two conversions?? What software would you use? I know this is basic stuff but I just need to know,
    thanks
     
  2. caucano

    caucano Regular member

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    I believe that any conversion from one form another results in loss of quality, especially if you are going from a large video file to a smaller one. for converting dvd files to avi's you should check the guides, they are very usefull

    http://www.afterdawn.com/guides/
     
  3. aldaco12

    aldaco12 Active member

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    MPEG compression is the standard for videos: mpeg-1 uses constant bit rate (CBR), is used for VCDs and has bitrate of 1150 kbps of video and 224 kbps (MP2) for audio. mpeg-2 is more subtile and is used for the SVCD's mpegs and the DVD's VOB files. SVCDs have the same audio stream of the VCDs but use Variable Bitrate (VBR) or video; since in general it is used for putting half movie (max 55' per CD, max 110' movies) in a 80' CD-R, the average bitrate value to but is about 2000-2200 kbps , but since you use VBR, YOU put the exact value so 1 CD of movie is 830 MB large and the movie fits into 2 CDs. If you want, you can split the movie into 3 CDs and the " <55' " movie doesn't exist no more [since all movies are < 165']).
    DVD VOBs are even larger, more complicated: CBR video; the (mulriple) audio streams included in the VOBs use more kbps, have a 48 kHz sampling frequency (not 44.1 kHz) and also are often in Dolby Suround (AC3).
    AVIs are usually a 'trade-off' between 'quality' and 'size'. Codecs 'tech' your PC the way to compress video, and the best ones are DivX and Xvid.
    The AVIs are usually compressed with 600-800 kbps, aave only one audio stream encoded in MP3/CBR audio (the MP3 compression of the AVI's sound stream must use CBR or the AVI --> mpeg conversion will create a movie who has the video out-of-sync with the sound) instead of MP2, and lets you choose the bitrate losing some quality.
    Due to the usual trade-off I prefer
    1) convert a 720x480(576) DVD movie to VCD resolution, first
    2) compress the 352x240(288) movie.
    because an excellently-compressed VCD movie gives you a better result than a badly-compressed DVD movie.
    Of course, in the net you find a good amount of, say, 600x400 excellent AVIs, 700-900 MB large, so there will exist a good trade-off of "movie's resolution Vs movie's size", but what I described above is my choice of behaviour, not an absolute 'rule'. In my way you 'approximate' less the movie, using the same bitrate, and since you often watch the movies which were downloaded from the net transforming them in (S)VCDs form, decreasing the movie's resolution before the AVI compression changes a little.....
    But this is not my job, ask to the DivX/Xvid or the DVD forums, first. Even when you transform WAV --> MP3 you lose a little quality (listenin to an original CD makes you appreciate a little more the sound than a MP3s-made one), but minor (128, 192 or even 256 kbps, no video...more simpler than movies).
     
    Last edited: Apr 18, 2005

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