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Old 23 Dec 2003, 12:00 PM   #1
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Question Bitrate/quality question.

Hello.

How high up in bitrate should i go when encoding a movie from dvd format to divx to maintain perfect quality in constant bitrate?.

Let's say i have a 40 min movie [dvd] and a 40 mins audio track [192kbs][ac3] about 55-60mb im guessing. If i then chose to have it encoded to a 700mb divx file with the audio track that would mean about 2100-2200kb/s sec right? would that produce a good looking video? or do i have to go even higher up in bitrates to receive a near dvd looking image?.
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Old 23 Dec 2003, 04:30 PM   #2
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For normal viewing on the computer, a bitrate of 1000 - 1500 kbps is usually enough.
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Old 24 Dec 2003, 02:46 AM   #3
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It may take some fooling around with different bitrates for you to get the quality you are looking for but for 40 minutes of video you will definitley be able to get good quality with 2000kbps. If size is a problem try lowering it and see how good it looks to you. It's all personal prefference as far as the quality question goes.
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Old 28 Dec 2003, 07:27 PM   #4
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The bitrate depends (directly proportional) only on resolution and on "motion".
If they're high (4example: an action movie @ 720*576), also the bitrate must be high

If you wanna be precise:
Bitrate=(BPF*resolution*fps)/1024
BPS depends on the kind of the movie (hi motion or not, anime or normal, etc) anyway BPF>0.20 for medium-high quality, BPF>0.25 for really high q., BPF=0.30 is too much.

4example: if you wanna compress a PAL DVD with a resolution of 680*384, the bitrate must be:
bitrate=(0.20*680*384*25)/1024=1275Kbps (or higher)

Anyway 2000k could be low only if you use a res of 2*3GIGAPixel!
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Old 28 Dec 2003, 07:33 PM   #5
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....but I'm assuming that you don't use constant bitrate

if you wanna have good quality, use EVER dual pass.
Thrust me, with constant bitrate (even if it's 2000Kbps), all hi-motion scenes will be full of noise and macroblocks
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Old 28 Dec 2003, 10:03 PM   #6
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I'm not using 2-passes 'coz it takes way to long.i'm trying to reach maximum quality in lowest possible time. right now im experimenting with 1-pass 100% Quality with GMC,Qpel and bidirectional encoding at a resolution of 720x400 each movie is about 40 mins long, the result im getting is a 1gig movie wich is fine with me since i'm just looking to get as close to dvd quality as possible.

Does GMC,Qpel and birectional encoding improve the quality of the movie much?
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Old 29 Dec 2003, 02:10 AM   #7
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Qpel SHOULD improve precision in data allocation, but imho it improves only the number of artifacts/noise

GMC SHOULD allow to reduce the bitrate needed in panning-zooming scenes, but I experienced that it reduces only the encoding speed

I haven't already tested them with 5.1.1, but I don't think that there could be differences...

I use only bidir. enc, it makes the video more fluid and it doesn't affect speed noticeably.

Use normal mode, benefits of slow and slowest are noticeable only with anime movies (noise decreases a little).
NEVER use psycho or resize-crop-deinterlace via codec.

and, if you wanna have max definition, use Lanczos resize.

P.s. trust me, dual pass enc is ALWAYS better and it's not so slow: 1st and nth pass (sing.) are faster than 1pass, so the time needed is less than double, as you may think.
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