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Old 2004-05-25, 18:35   Link #1
Oiseau
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Join Date: Jan 2004
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A question : Exactly what are codecs?

I've been downloading BitTorrent anime episodes (avi format) for 6 months now, and I'm still unclear on the concept of codecs. Yes, I know it means enCOder/DECoder, and I know you need the right codecs to play video files encoded in certain ways. I know there are audio and video codecs, and I know that there are many kinds.

My question is : exactly what are they ?

Are they DLL files ? OCX files ? Programs which reside in RAM ? Drivers ? Background OS processes ? How (and where) can you determine if they're installed on your computer ?

And while I'm here : Why is it said that programs like FFDShow and VLC can play "any video format out of the box" ? Don't they need the codecs too ? I've heard it said that they "include" the codecs, but how is that possible for recent codecs released after the program itself ?

And why is it a bad thing to install too many codecs ? Doesn't every AVI file use the codec it needs, to the exclusion of all others ?

Anyway, I'd like to get a clear answer once and for all. I don't like using computer stuff without understanding what it is.

Please, no sarcastic replies like "Google is your friend".

The Oiseau
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Old 2004-05-26, 01:06   Link #2
Cruzz
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Quote:
Originally Posted by Oiseau
Are they DLL files ? OCX files ? Programs which reside in RAM ? Drivers ? Background OS processes ? How (and where) can you determine if they're installed on your computer ?
(this is only applicable for Windows as I don't really know how codecs are packaged for Linux)

The vfw* part of codecs is generally a DLL while the directshow decoder is an ax file. You can generally determine what codecs you have installed by browsing through your system32 folder, the installers tend to put the core codec in there even if you try to install them elsewhere in the system. They also tend to leave some kind of mark in the registry. In any case, a more reliable way is to use programs such as Gspot.

*video for windows, used for display in certain programs (like for example virtualdub) and for encoding, players generally use directshow

Quote:
And while I'm here : Why is it said that programs like FFDShow and VLC can play "any video format out of the box" ? Don't they need the codecs too ? I've heard it said that they "include" the codecs, but how is that possible for recent codecs released after the program itself ?
VideoLan and FFDShow are both based on libavcodec, which is an open-source library containing encoders and decoders of various video (and audio) streams. I don't know of the inner workings of libavcodec but I believe that it uses a general purpose MPEG-4 decoder for all the MPEG-4 codecs (xvid, divx, wmv8, wmv7). MPEG-4 codecs are fairly standardized, generally speaking you can decode any xvid file with divx and any divx(4/5) file with xvid. Of course in reality this isn't always the case, various things break this interoperability from time to time. Still, it does work a lot of the time.

Quote:
And why is it a bad thing to install too many codecs ? Doesn't every AVI file use the codec it needs, to the exclusion of all others ?
Some codec packs in particular seem to have lots of problems with interference, don't really know why. I also don't really know why some people have a weird fetish with installing a million and one codecs, I myself only have xvid and ffdshow installed and I can do pretty much anything with just those two.

Last edited by Cruzz; 2004-05-26 at 15:37.
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Old 2004-05-26, 13:23   Link #3
KeinikuSuki
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Cruzz did a mighty fine job, but I have one thing to add.

Quote:
Originally Posted by Oiseau
How (and where) can you determine if they're installed on your computer ?
Download and install the GSpot Codec Information Appliance (no, despite the name, it's nothing disgusting). You can get it from the offical site here. (It's kinda hard to find the download link so I'll include that link too)

Once you have it installed, Open the View Menu and choose "Installed Codecs ->". Then you can choose Video or Audio.

GSpot has other uses. For example it tells you which codec actually decodes a given avi file. It also gives handy information like FPS, BitRate, Aspect Ratio, and tons of other fun stuff. Well worth the download.
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Old 2004-05-30, 15:57   Link #4
remase2
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Join Date: May 2004
so if you have divx codec you would also need ffshow codec to play certain files?
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