Need explanation of codecs

What Noodle · 5 Sep 2006 at 19:27

I understand the basics of codecs like what they are and how they work on a very basic level, but I'm looking for some more detail on how they encode/decode content. Do all codecs use PCM to encode? When you download a MP3 file from the Internet, is it already coded and ready for the player to decode it? Any information would be greatly appreciated. Thanks!

bledd · 6 Sep 2006 at 00:48

wikipedia probably has all the information you need, google for that site

you can search for items on there

if i was explaining a codec to someone who had no idea (i'm assuming you do by the way,,) i'd say a codec is like a language, a file (or song) is downloaded in a language, if the pc doesn 't understand it, it won't even try to open it, if you download the codec (or dictionary) for it, then the computer will know what is going on and will read it with no problems

-yes its already coded for the player/codec/filter to decode it

, hence the small filesize

codecs are used for compressing (and therefore reducing file sizes) of multimedia files

a codec is not always associated with media though, compression programs like 7zip use codecs to compress and decompress the files they use

-edit, welcome to the forums

What Noodle · 6 Sep 2006 at 19:51

Thanks for your info! Yeah, I've read over Wikipedia, but there were just some aspects that I didn't understand from the articles. I think language is a very useful analogy to codecs, so I'll use that to explain it. One more question: what format are CDs are coded in?

Runbalk · 6 Sep 2006 at 21:36

What Noodle said:
One more question: what format are CDs are coded in?

I'm not sure if CDs are coded in a single format. I thought there where different formats like CD-ROM, CD-RW, CD-R, etc. (is that sort of thing what you're wondering about?). And I thought it could go a step further whereby any one of those formats could be encoded into a certain language e.g. some sort of data cd, that your PC, but not your HiFi, would understand (is this the type of thing you're wondering about?).

Sorry if that just makes it more confusing.

By the way, cool name - that episode of HIGNFY was fantastic

What Noodle · 6 Sep 2006 at 22:17

Runbalk said:
I thought there where different formats like CD-ROM, CD-RW, CD-R, etc. (is that sort of thing what you're wondering about?).

I guess my question was when content is put onto a CD, is it compressed first? Or are songs, for example, in a WAV format where they are not compressed? If a single track is extracted from a CD and onto a computer, what codec format is it in?

Yeah, I liked that HIGNFY episode too, obviously. Pot pot pot noodle

Energize · 6 Sep 2006 at 23:39

An audio cd is in the uncompressed PCM format.

Una · 7 Sep 2006 at 00:13

If there's anything specific you wish to ask about encoding feel free. There is a hell of a lot of formats out there. If you wish to write something pretty easy start by writing a huffman encoder, this is used in many encoding algorithms (i.e mp3 etc..). As far as I know most CD audio is still raw uncompressed wav/PCM files. You generally have lossy and lossless encoding. Data such as music can be compressed using a lossy algorithm at the expense of sound quality. Where as file compression really needs to be lossless otherwise you would loose data

I can provide you some links/videos on compression but they are really for programmers.

What Noodle · 7 Sep 2006 at 17:01

I am now enlightened. I'm not wishing to create my own code; I just have to give a presentation explaining codecs in minimal depth but beyond Wikipedia's basic information. Thanks for everyone's help!

basmic · 7 Sep 2006 at 17:24

What Noodle said:
I am now enlightened. I'm not wishing to create my own code; I just have to give a presentation explaining codecs in minimal depth but beyond Wikipedia's basic information. Thanks for everyone's help!

So this thread was really a "do my homework research" thread? :rolleyes:

Energize · 7 Sep 2006 at 17:37

basmic said:
So this thread was really a "do my homework research" thread?

It clearly wasn't but so what if it had been? People here are always happy to help.

basmic · 7 Sep 2006 at 17:44

Otacon said:
Remember, we're not here to do your homework for you.

Energize · 7 Sep 2006 at 18:01

Well he doesn't speak for all of us. Secondly theres nothing in the forum rules against it. And the thread was a question about codecs not a person asking for someone to write them an essay, would it be different it the question was just out of curiosity rather than research purposes?

Runbalk · 7 Sep 2006 at 19:26

basmic said:
So this thread was really a "do my homework research" thread?

Woah, how did you come to that conclusion? What if someone like Bill Bryson wanted to give a presentation about microchips to a bunch of people? Since it's not his area of expertise, it would seem sensible to me for him to go read up about the stuff and ask the experts for their opinion and get more info about it.

Another example would be if I went to the doctor and asked how I could get rid of a liver disease. The doctor shouldn't turn around and say, "You figure it out!".

You're simply jumping to conclusions.

whitecrook · 7 Sep 2006 at 20:18

CODEC is short for Code(r) Decode(r). So all a codec does is take some data, encode it. and the 'dec' part which is to take the coded data and decode it.

Simple really.

Of course the difference between all the codecs, is how and what they can encode.

What Noodle · 8 Sep 2006 at 17:02

Does the average listener/viewer really notice a difference between the various formats? I can hear a difference between Dolby and DTS, for example, but I don't pick up major differences between WMA and AAC. Any thoughts?

P.S.: Thank you, Energize and Runkbalk

squiffy · 8 Sep 2006 at 17:06

What Noodle said:
Does the average listener/viewer really notice a difference between the various formats? I can hear a difference between Dolby and DTS

Reduce rears and subwoofer gain by 3dB in the DTS mode, then try comparing them again.

Energize · 8 Sep 2006 at 17:14

What Noodle said:
Does the average listener/viewer really notice a difference between the various formats? I can hear a difference between Dolby and DTS, for example, but I don't pick up major differences between WMA and AAC. Any thoughts?

P.S.: Thank you, Energize and Runkbalk

Yes definatley, at low bitrates espically, theres a huge difference between a 64kbps ogg file and a 64kbps wma file, the wma file sounds awful in comparison. On higher end equipment you can tell the difference between 192kbps and 320kbps.