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Old Mar 17, 2008, 10:58 AM   #1
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Hi, I am a newbee. I take a lot of videos using my camera. One of my cameras, Kodak, saves video files in .mov format. My other camera saves the videos in .avi format. Itseems to me the .avi files takes a lot more disk space than the .mov files for the same amount of video time. It also seems to me that the .avi file is slightly better quality than the .mov format (still need to be verified).

Can someone tell me what video format uses the least disk space for the same picture quality as disk space is important to me since I store everything on my laptop and disk space is limited.

Also, please let me know what camera manufacturers use that best format that you recommend.

Thanks in advance.
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Old Mar 17, 2008, 12:01 PM   #2
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simple rule of thumb.........better quality = big file size.

no way round that one im afraid

if u need more space then the only answer is bigger or multiple memory cards

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Old Mar 18, 2008, 12:13 AM   #3
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vhdp, do you have a DVD burner? If so, why not just archive to a DVD and free up hard drive space?

To answer some of your question:

AVI and MOV are container formats . As stated before one can't answer the question which one of the format has better quality because it depends on the codec used in the container. Follow the wiki-links for better understanding ;-)

If you want to see the page where that quote comes from....


...and go to the bottom of the page.

There are many video format converter/compressors (like the freeware SUPER), but like Reanimator said, quality relates to file size. I don't know enough about the subject to tell you which container format/codec combo' will deliver the highest quality at the highest compression rates. You might need a digital video forum for a really good answer.

And if it turns out that to get this best combination you have to convert your videos into another format and use a different codec and compression scheme, would you be willing to do all that to save some disk space?

Sounds easier to me to archive to a removable disk or get a compact external hard drive for your laptop.

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Old Mar 18, 2008, 11:46 AM   #4
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When it comes to compression schemes, the basic rules of thumb are pretty straightforward: First, any compression scheme that is "lossless" will give you excellent images but take the most space. An example of this type of compression is run-length encoding. In lossless compression, you get back exactly the same image that you compressed when you uncompress it. While the amount of compression varies with the image content (true ofmost compression schemes, whether lossy or lossless), the usual rule of thumb is that you can expect to get compression of about a factor of 2.5, so a 100 MB clip (ashort clip of about 3 or 4 seconds' duration) would typically compress to about 40 MB.

Next up the food chain are compression schemes that are intra-frame lossy. An example of this kind of compression is motion JPEG. It compresses each frame of the video independently. When you uncompress the video, you don't get the exact same image back -- it has lost some of its information.Intra-frame compression schemes will typically yield a factor of ten compression before people start to feel that the image quality has suffered noticeably. So our short clip would go from 100 MB down to 10 MB.

The final step in compression technology is inter-frame compression. In this kind of scheme, the algorithm uses other image frames to predict the content of a given frame. If you think of a typical movie, the thing that is most like a given image is the image that was taken just before or after the current one. By allowing the algorithm to consider how similar a given image is to the ones next to it, you get a HUGE improvement in compression. An example of inter-frame compression is MPEG. Typical compression rates that can be achieved this way are 100:1, so our 100 MB clip is now down to 1 MB.

But nothing is free. MPEG not only requires more computational power to perform than the other methods, it tends to fall apart under non-linear editing ("film editing," where you cut out part of the film clip, change the time base, etc.). The problem is that you have to uncompress the images, then re-lossy compress them at the cuts. This results in "generational loss," which is when you repeatedly lossy-compress the same file [NB: This is NOT true of intra-frame lossy compression when you cut out some of the images]. So, if you plan on editing your vacation movie, MPEG has this big disadvantage. It is a big plus if you just show the clips without editing them, because it is so much smaller than other compression schemes.

People will go on at great length about whichcodec is the best. By and large, they are blowing smoke. The real differences reside in the KIND of compression scheme. If you decide which of the above kinds of compression scheme best fits yor use, you can pretty much select any codec that uses that approach and you'll be fine.
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Old Mar 28, 2008, 5:06 PM   #5
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Point of interest - Kodak uses MPEG4 and at least the Canon S3/S5 use motion JPEG. The file sizes and quality exactly track tclune's explanation.

By the way tclune, thank you for your very lucid explanation.
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