I'd like to know how to compute a bitrate for a given resolution, source VOB size, and target AVI size.
For example, suppose I have 4.7G worth of VOB content (which was generated using DVD shrink to exactly fill a single layer dvd). I want the resulting Xvid AVI to fill a single 700 MB CD right to the brim. Without scaling the resolution, what bitrate would I set gui4ffmpeg to? Is there enough known variables to solve this, or do I need to figure out what bitrate the source is first?
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How about using the Search Tools facility (https://www.videohelp.com/tools) to search for a bitrate calculator? The result of such a search would lead you to https://www.videohelp.com/tools?toolsearch=bitrate+calculator&s=&orderby=Name&hits=50&c...res=&listuser=, and then you could check out the VideoHelp Bitrate Calculator (https://www.videohelp.com/calc.htm).
Search is your friend! -
Originally Posted by mill48
btw- I'm skeptical about the second calculator you mentioned, which is a java app served from videohelp.com, because it does not account for the number of pixels.
Originally Posted by junkmalle -
Originally Posted by jgombos
Suppose you're going to drive 50 miles an hour for 2 hours. How far would you go? Does it matter how big your car is? -
Originally Posted by junkmalle
Originally Posted by junkmalle
If you're logic were applicable, you could encode a movie at 16,000 x 9,000 pixels, and fit it all on a CD. You could then store an array of 15 or so movies in that space, and get 15 movies on one dvd. Heck, if resolution can be neglected, I can store every dvd in existence on a single dvd. -
jgombos,
Your original question wasn't asking how to determine the best compromise of image size and bitrate, for a given filesize. You asked "Without scaling the resolution, what "bitrate would I set gui4ffmpeg to?" I gave you the equation that answers that question.
If you compress an hour long 1600x1200x60fps video and an hour 320x240x30fps video both at 1000 kbps you will get 450MB files (excluding audio). The 1600x1200 video will not look much like the source. The 352x230 image will look a lot more like its source.
1000 kbps = 1,000,000 bits per second
1 hour = 3,600 seconds
1,000,000 * 3,600 = 3,600,000,000 bits
divide by 8 to get bytes
3,600,000,000 / 8 = 450,000,000
If you want to know what combination of bitrate, frame size and frame rate will get you the best quality image -- I can't answer that for you. And neither can anybody else. The answer depends on the video in question and what "quality" is in your eyes. -
Originally Posted by jgombos
The reason why files with bigger resolutions tend to be bigger in filesize is because they tend to have a bigger video bitrate, to allow for the bigger resolution so that quality is retained
As far as the calculation itself goes, resolution plays no part whatsoever. However you need to choose a suitable resolution for your bitrate or a suitable bitrate for your resolution if you want quality video that doesn't have pixelation and macroblocks through it everywhere. By the same token there is such a thing as overkill as well. The Videohelp.com Bitrate Calculator is fine to use, and is a godsend.
Originally Posted by jgombosIf in doubt, Google it. -
I'm not too impressed with the results of these calculators. The best result produced a 650 MB file when the target was 700 MB. The worst result so far was a 559 MB file, when the target was 700 MB.
I can understand that variable bit rates probably cannot be handled with too much precision, but these underestimates seem excessive.
DVD Shrink his the target filesize right on the money every time. I suppose it has the advantage of being able to change the target bitrate on the fly as the end nears. Are there any VOB to AVI/Xvid tools that do that? -
Does anyone know a way to use the results of an unsuccessful conversion to compute a better bitrate? I'm tempted to try a linear equation. ie a bitrate of 1083 produced 559 MB, so I should step the bitrate up to 1356. I'm just wondering if it would make any sense to try to incorporate the original formula in that.
update: The linear equation did not work. I ended up with a 630 MB file. -
Originally Posted by jgombos
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Originally Posted by junkmalle
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Originally Posted by Abond
update: Bitrate accuracy does not seem to be the problem here. I encoded a file targetting 1356 kbps, and VirtualDubMod reports that the file is 1364 kbps. That seems to be reasonably close to what I asked for. Yet the size is nearly 70 megs less that the calculations projected.
So the next question is - how does VirtualDubMod know what the bitrate of a file is? Does it measure this value, or does it merely trust a (potentially flawed) header value?
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