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Old September 27th, 2006, 05:52 AM   #1
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one pass or two?

If file size doesn't matter, will a single pass CBR give you as good or better (?) quality that a two pass VBR?

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Old September 27th, 2006, 08:16 AM   #2
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Same quality, bigger size.
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Old September 27th, 2006, 11:55 AM   #3
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I've heard that when filesize doesn't matter, VBR and CBR will give you the same sized files in the end (maximum quality). CBR will encode faster because it won't be doing as much calculating.

But I could be wrong.
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Old September 28th, 2006, 08:18 AM   #4
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That is not true. In VBR you specify the average bit rate, so you can control the resulting file size. It is just that with two passes you can allocates those bits more efficiently, thereby improving the quality.
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Old September 28th, 2006, 04:13 PM   #5
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Quote:
Originally Posted by Robert Bobson
If file size doesn't matter, will a single pass CBR give you as good or better (?) quality that a two pass VBR?

Thanks

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Size of the project is the deciding factor. If it's a short piece, you can successfully use CBR at a high bit rate that will be as good as if not better to most VBR encodes. Above an hour of material you will be better off using VBR just so you can fit the video and keep the quality high.
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Old September 29th, 2006, 05:34 AM   #6
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thanks for your responses ~
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Old September 29th, 2006, 09:38 AM   #7
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Yes the quality can be better with 2 pass encoding. The reason for this is with a single pass the encoder has to do a rough estimate of what bitrate to use and it has to do it fast. A single pass may give a certain frame a bitrate of 5.5 mbits/s. A 2 pass encoder will give the first pass 5.5 mbits/s but then in the second pass realize that a 5.7 mbits/s may work better. This is a very small amount but it is higher and could mean the difference between a few macroblocks or not. This is even more true when dealing with low bitrate DVD's such as 4.5 mbits/s. At that rate every tiny bit can help.

The 2 pass also helps in that the certain frame at 5.5 may give the same amount of quality at 5.3 so that leaves a tiny bit of space left to add more bits to another section that needs it. This is why the Cinema craft encoder can do up to 8 (It may be higher) passes. Every pass it does it can really get down at nit pick the very best bitrate to use for every single frame. Every new pass the results get more accurate and fine tuned. Above 2 passes however you would really have to be a quality freak to care about the difference and I'm sure most people would never be able to tell.
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