10-12-2005, 11:23 AM
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Join Date: May 2004
Location: New Mexico, USA!
Posts: 10,709
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Originally Posted by Tim L
First of all, all three options produced a video stream described as "MPEG-2 MP@ML VBR". I assume this means we get a Variable Bit Rate. Does this also suggest that the results below -- especially the average values, might be highly dependent on the content of the video -- ie how much motion there is, how many scene changes, etc.? I'm thinking, but I'm not sure, that the resulting average bit rate in VBR could end up low because it really didn't need any more data to render a scene with little motion in it (ie slow pans on a still photo).
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My explanation in simple terms is that MPEG is a compression technique which does not have individual frames. A frame (frame 1 for example) is compressed. The following frame (frame 2) only has the data which has changed from frame 1, and it goes on to frame 3 etc. So slow pans could actually have a lot of changes if you view one point in the sequence of frames. Trying to guess what the encoder is going to do can be challenging.
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Originally Posted by Tim L
Okay, now do any of you experts want to comment? (I'm ready to learn something! You have a willing student!) Does anybody know what "Q.Level" is? I assume lower numbers are better, as Option 3 with the higher bit rate has a lower value.
Also, what does the "MP@ML" part of the stream description mean?
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From http://tangentsoft.net/video/mpeg/enc-modes.html :"The quantization (Q) level of an MPEG stream is a measure of the amount of data the encoder threw away to bring the bit rate down. Higher Q values mean the encoder threw away a lot of data, implying a low bit rate, but also low visual quality. A low Q level implies a high bit rate, and high visual fidelity."
From http://www.dvd-software.info/dvd-ar...-glossary/4.php :"MP@ML - Main profile at main level. The common MPEG-2 format used by DVD (along with SP@SL).
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Originally Posted by Tim L
Oh, and no, I didn't burn all three to a dvd and watch it on a TV to see if I could tell the difference. That would be a sensible thing to do, but would take some more time.
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That is the proof in the pudding if you are going to end up with DVD's to play on a stand alone DVD player connected to a TV.
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Originally Posted by Tim L
And I just spent a bunch of that time typing in this post.
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Me too, which is why I skipped a lot of areas.
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