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  1. Member
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    Mar 2005
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    Boston, MA
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    Originally Posted by major
    Enable cabac and b-frames, then disable "constant bitrate", and set qmax=qmin=22. Or even use 21 or 20 for a little more quality (there is no much point about lowering it too much, though).
    I got a question on this tip. I've found in the past, x264 via Handbrake, that sometimes going constant quality can cause high 'instantaneous' bit rates. Slower computers can then choke on playback and drop a bunch of frames. Typically this problem can occur with lots of action/motion (something like sports) and/or lots of detail (something like a large school of fish). In this situation, a fixed bit rate can actually work fairly well, one would lose quality in that scene in the encode instead of dropping frames on playback.

    However I usually don't really care about bit rate and 'quality' is nice way to abstract it. But I encode a lot, so I don't always have the time to review the result for the above issue. Is there a way to specify a cap for the bit rate when constant bit rate is off?

    Also, what happens if I don't specify qmin=qmax with constant bit rate off? Does qmax not matter or does it somehow vary between qmin and qmax? based on what?

    Thanks for the help!
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  2. Member
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    Regarding the vob. encoding to H.264 to increase quality even further, you advised me to turn on 'Print PSNR' and to look for the result value in the info doc. that comes with every encoding, to look for it at the final part. Would it be possible to be more specific? Which number to look for?

    Best Regards

    hito
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  3. Originally Posted by cicero
    Is there a way to specify a cap for the bit rate when constant bit rate is off?

    Also, what happens if I don't specify qmin=qmax with constant bit rate off? Does qmax not matter or does it somehow vary between qmin and qmax? based on what?

    Thanks for the help!
    In variable bitrate mode, the bitrate is completely free to vary within the constraints given by having a fixed quantizer. qmin must be equal to qmax. The higher the quantizer, the lower the average bitrate.
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  4. Member
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    Originally Posted by major
    In variable bitrate mode, the bitrate is completely free to vary within the constraints given by having a fixed quantizer. qmin must be equal to qmax. The higher the quantizer, the lower the average bitrate.
    Ok, cool. A follow up question: Does 2 pass help at all for a constant quality encode, qmin=qmx? (In Handbrake it doesn't, and I think the 2pass option is greyed out when you pick constant quality.)

    Thanks!
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  5. Indeed, it makes no much sense to use 2-pass in variable bitrate mode. I should also gray it out when variable bitrate mode is selected.
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  6. Member
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    Sorry for my persistance on this situation, on the document that comes with each encode, with print PSNR selected, in the end of the document which number or reference should I look for that tells me the value to increase the quality?
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  7. It is the number in bold in the line reading like the following:

    x264 [info]: PSNR Mean Y:35.60 U:46.24 V:48.60 Avg:37.21 Global:37.11 kb/s:884.3
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  8. Member
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    Hello again,
    if I use CABAC on H.264 encoding with Qmin=Qmax=20 is it probable that the encoding quality will be increased?
    The VOB. file in question has been extracted from a movie DVD.
    Regards
    hito
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  9. Member
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    Please advise me on this, do you think that if the VOB. file is from a DVD movie will I still need to use any of the filters for the H.264 encoding?

    hito
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  10. CABAC lead to smaller files at same quality. Filters should not be needed with VOB sources.
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  11. Member
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    Could it be possible to give a hint on the solution fot the email I have sent some days ago?

    Regards

    hito
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