Confused about Panny VBR recording

Discussion in 'Blu-ray & DVD Players & Recorders' started by saturday, Apr 10, 2005.

  1. saturday

    saturday
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    Hi,

    I've searched through the forum and can see I'm not the only one that's confused.

    When copying material from my sky+ to DVD I tend to use the Variable Recording feature with DVD RAM. What confuses me is that sometimes this results in a "full" disk, sometimes as little as 3.2 gig when copied to DVD-R (with TMPGEnc).

    I have the VR set to auto and have deduced that this accounts for the varying amount of data (due to the machine "guessing" the best bit rate). I've also deduced that if I set the VR to fixed then this would use the full capacity.

    But which is better - fixed or auto? Auto should be better shouldn't it, but then surely using the discs full capacity is better than a 80+percent fill?
     
  2. Steve.J.Davies

    Steve.J.Davies
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    me too ! I can see the benefits and I can see that sometimes the disk won't fill up as it depends on the data.
    but..
    how can it do this in a single pass ? surely it would have to pass through the datastream twice (at least). or does it keep all kinds of sophisticated 'profile' info on the disk as it records....
    I know I can get good quality on the pc if I sit and use sophisticated software that does do double passes and lets you set all kinds of parameters.
    Anyone know how (or if) the panny boxes optimise a VBR datastream ?
     
  3. saturday

    saturday
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    Well I'm still confused!

    The last few disks I've chosen fixed vbr and still the amount of data is varying.
     
  4. TobyW

    TobyW
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    The "fixed" VBR just means the resolution is fixed. That is, it's fixed at 704x576 or 352x576 or 353x288 for the whole recording (depending how many minutes have to be fitted on the disk), instead of flicking between these resolutions during the recording.

    Even though the resolution is fixed, the bit rate will still fluctuate. It will rise for high-action scenes and fall for low-action scenes.

    In 2-pass recording such as you might do off-line on a PC, the first pass generates a profile of the amount of action throughout the program. From this, the average bit rate that will fit the recording nicely on the disk can be calculated, to be used for the second pass.

    However in single-pass recording (needed for real-time encoding), the encoder has to guess the bit rate up front without knowing the action profile. Either the bit rate must be fixed (as in some PC encoders), or a bit rate for VBR must be picked out of the air, leaving some margin for error.

    When the VBR recording has been completed, it will be found that the actual length (in bits) will differ from the margin by a positive amount for high-action recordings, or a negative amount for low-action recordings.

    Although some space is wasted, this still seems to give a better overall result than if a constant bit rate (CBR) had been used.

    Hope this helps.
     
  5. Rasczak

    Rasczak
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    The Variable Bitrate Function is not something any of you should be worrying about. This is an automatic function and not something you have any real influence over - other than setting the VBR Resolution to 'Fixed' or 'Auto' (set it to Fixed!) - and you use it whether recording in XP or any other mode.

    When archiving from Sky+ you need to be using Flexible Record. I have written a brief article on the subject here.
     

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