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Optimal KB/S

Discussion in 'Other video questions' started by mikerd, Jul 23, 2002.

  1. mikerd

    mikerd Member

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    Ok. So let's extend a question I've seen pogoed around the discussion groups. I want to back up some DVD's. Not (yet) having a DVD burner I've been backing them up in DIVX format, hoping at a later point to burn from there back on to DVD's when I get a DVD burner (or multiple VCD's should I never get one :( ).

    For the DIVX encoding, I've been wondering, do I use 1CD/movie, 2CDs?, 3CDs?. Is there some rule of thumb, or some experience people have had as to what data rate (kb/s) is good to give you better transference later to VCD / DVD? I know somebody is going to tell me, the best solution is to use 7CD's and backup the VOB files, but that's not particularly helpful. Any helpful ideas or comments?
     
  2. dRD

    dRD I hate titles Staff Member

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    If you really have plans to burn the movies on CD as temporary solution and later on re-encode the movies and put them on DVD-R in order to watch them with stand-alone DVD player, then _don't_ use DivX.

    DivXs need to be re-encoded, which will make the quality suck big time, when they're transferred to DVD-R as DivX is essentially MPEG-4 and DVD players support only MPEG-1 and MPEG-2 standards.

    Also, the picture size and other aspects need to be considered. VideoCD can be transferred to DVD-R without re-encoding the video, but the audio needs to be re-encoded to use 48kHz instead of VCD's 44.1kHz as VCDs only support 44.1kHz and DVDs only support 48kHz. But the VCD resolution MPEG-1 video qualifies 100% as DVD-R compatible video.

    And SVCDs are complicated issue as well, because while SVCDs are MPEG-2 just like "normal" DVD-Video discs, but the resolution of SVCDs which is 480x480/576, is not supported by DVD standards. And the audio thing applies in here as well -- SVCD supports officially 44.1kHz only and DVD only 48kHz.

    What I've found the best temporary storage method that doesn't require video re-encoding, but provides good quality video and works on CDs _and_ DVDs when played with stand-alone, is called "CVD" or "China Video Disc" -- one of the official drafts for standard that became eventually known as SVCD. CVD's specs are almost identical to those of SVCD, but the video size is different -- 352x480/576 -- which _IS_ supported by DVD-Video standards. And most of the DVD players that play SVCDs, play CVDs as well. Only problem is with the audio, but you can try to hack it and make it 48kHz already when making the CVD, even that this violates the specs.
     
  3. mikerd

    mikerd Member

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    Hmmm... Interesting. So although DIVX really provides the best opportunity for maintaining the high-resolution of DVD's (720x480) (640x360) the re-encoding will really garble things up. Not good.

    I've never tried the SVCD format before. Perhaps the medium resolution on that would make it a good choice. On the flip side, I can always pray that a DVD player will come out that supports the MPEG4 standard *G*

    Back to the original question though, how concerned should we be with the KB/s used for the encoding? What are the boundaries between crappy and decent? It would be nice to be able to say, "Well, this movie is only 90min, so I can put it on only 1CD, but this 110 minute one should be split onto 2.

     
  4. dRD

    dRD I hate titles Staff Member

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    The bitrate thing depends totally on format. For SVCDs and CVDs I generally use 1900-2100 average bitrate, but as MPEG-2 takes more space anyway, DivX can do fine with lower. Normally I would use a rule of thumb that 90mins or less should be fitted on one 80min CD with DivX and longer than that would require two CDs. But then again, I'm more quality freak than saver -- I consider that spending $0.00001 to one additional CD (or whatever they cost nowadays, cheap anyway, I give more money to local bums on subway daily anyway :) is worth it if I get better quality.
     

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