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Old 19th March 2011, 05:40   #1  |  Link
MacroBull
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Bitrate mode better?

Among qp,crf,bitrate mode,which is better to use?
I don't know the difference in ripping result between qp and crf,who can tell me?
I think bitrate can control all the options,it can give the best ripping result,it can be even changed toward qp mode,is that right?
As for presets,under qp or crf mode,is it that change the persets can only lower the bitrate but not improve quality?

Another question about anime deblocking in rapid scene, dark scene and fade scene, I met a lot of block and increase bitrate/deblocking,psy rf,trellis doesn't help.It seems increasing Adaptive quantizer reduced the block,why?
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Old 19th March 2011, 11:04   #2  |  Link
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If you need a known size, use 2-pass bitrate, otherwise crf. Do not use qp. 2-pass and crf will give you the same quality at the same bitrate.

Presets change the the quality/bits. So when using crf the exact visual quality can be affected by your choice of preset.

The general suggestion for animation is to lower psy-related values. Try --tune animation.
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Old 19th March 2011, 11:05   #3  |  Link
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Quote:
Originally Posted by MacroBull View Post
Among qp,crf,bitrate mode,which is better to use?
CQP is rarely a good idea, but otherwise it depends on what you are targeting. CRF is good for maintaining constant quality across a number of encodes. 2-pass lets you pick a target file size.

Quote:
I don't know the difference in ripping result between qp and crf,who can tell me?
http://mewiki.project357.com/wiki/X264_Settings#crf

Quote:
I think bitrate can control all the options,it can give the best ripping result,it can be even changed toward qp mode,is that right?
CRF and 2-pass give the same quality/bitrate. Both can be tuned towards CQP by using qcomp closer to 1.0.

Quote:
As for presets,under qp or crf mode,is it that change the persets can only lower the bitrate but not improve quality?
Both quality and bitrate can change, but slower presets give higher quality/bitrate.

Quote:
Another question about anime deblocking in rapid scene, dark scene and fade scene, I met a lot of block and increase bitrate/deblocking,psy rf,trellis doesn't help.It seems increasing Adaptive quantizer reduced the block,why?
AQ redistributes bits within the video, so that flat, low-complexity areas get more than they would otherwise.
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Old 2nd April 2011, 10:13   #4  |  Link
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about PB ratio,in 2nd pass bitrate mode,MB tree can calc the best,but use crf,you should input it?
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Old 2nd April 2011, 11:59   #5  |  Link
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What? If you use mb-tree, it will choose the pb-ratio for you. Otherwise, don't change it.
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Old 6th April 2011, 18:21   #6  |  Link
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http://www.mplayerhq.hu/DOCS/HTML/en...feat-x264.html
Quote:
7.5.1.3. Options pertaining to miscellaneous preferences

Two pass encoding: Above, it was suggested to always use two pass encoding, but there are still reasons for not using it. For instance, if you are capturing live TV and encoding in realtime, you are forced to use single-pass. Also, one pass is obviously faster than two passes; if you use the exact same set of options on both passes, two pass encoding is almost twice as slow.

Still, there are very good reasons for using two pass encoding. For one thing, single pass ratecontrol is not psychic, and it often makes unreasonable choices because it cannot see the big picture. For example, suppose you have a two minute long video consisting of two distinct halves. The first half is a very high-motion scene lasting 60 seconds which, in isolation, requires about 2500kbps in order to look decent. Immediately following it is a much less demanding 60-second scene that looks good at 300kbps. Suppose you ask for 1400kbps on the theory that this is enough to accommodate both scenes. Single pass ratecontrol will make a couple of "mistakes" in such a case. First of all, it will target 1400kbps in both segments. The first segment may end up heavily overquantized, causing it to look unacceptably and unreasonably blocky. The second segment will be heavily underquantized; it may look perfect, but the bitrate cost of that perfection will be completely unreasonable. What is even harder to avoid is the problem at the transition between the two scenes. The first seconds of the low motion half will be hugely over-quantized, because the ratecontrol is still expecting the kind of bitrate requirements it met in the first half of the video. This "error period" of heavily over-quantized low motion will look jarringly bad, and will actually use less than the 300kbps it would have taken to make it look decent. There are ways to mitigate the pitfalls of single-pass encoding, but they may tend to increase bitrate misprediction.
Happen to come across this and was wondering if this is still applicable.
If so, does that means that 2-pass > crf any time?

I remember reading a post by DS that states that an encoded output of the same size by x264 from the same source has the same quality regardless if it is encoded using 2-pass or crf assuming both uses the same encoding settings.

Can someone verify if the documentation of mplayerhq is valid?
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Old 6th April 2011, 18:29   #7  |  Link
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The text is valid if you are aiming for a specific bitrate/filesize. It's pretty clear that they are not talking about CRF anyway, because the problems described in the second paragraph are not applicable to it.

Last edited by nurbs; 6th April 2011 at 18:33.
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Old 6th April 2011, 18:35   #8  |  Link
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That section refers to one-pass ABR encoding. Not to one-pass CRF encoding.
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Old 7th April 2011, 05:12   #9  |  Link
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@nurbs and Didee
Thanks for the clarification.
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