codec vs file format

Caleb11 · 10-15-2009, 12:40 PM

hi,

what is the difference of codec and file format?
i know the basic but it's not enough to understand the two.

thanks.

ebackhus · 10-15-2009, 07:37 PM

Say you have a file called funny.avi. AVI is the container format, but does not dictate what codec was used. H264, XviD, and many other codecs could have been used to create the file.

**zuluclayman** · 10-15-2009, 10:14 PM

to expand a little on what Koala says - the file format tells you which type of container the file uses as a transport medium. This may be avi (Audio Video Interleaved) or .mpg, .mov etc. This determines the way the information is stored and delivered.
The codec (Compression Decompression) is the algorithms used to firstly compress the video information then as you want to play it to decompress the information - a little bit like going on holidays - you get your clothes, squash them down to fit in your suitcase down then unpack again.
Video files (and to a much lesser extent audio files) are huge if uncompressed - just imagine how much information is needed to describe the position, colour, size etc of every pixel for every frame of a video! then add the audio stream and you would have massive file sizes, making it almost impossible to store and/or transport (either to have as portable files or as in streaming or downloading from the net) these files.
Codecs, to a large extent, determine the file size end quality of the video you watch. If some of the older codecs are used they will not have been able to bring the file size down and retain quality.
The newer codecs such as xVid, DivX, H.264 are able to bring file sizes down dramatically while keeping fairly high quality video - this allows us to store, transport, stream and download high quality video much, much more easily than ever before.

Hope this helps

**blah789** · 10-16-2009, 04:01 AM

container = wrapper (file format)
inside it you can have various streams (usually audio and video, but you could have multiple audio streams (diff languages), subtitles, or other kind of streams)
codec = compressor-decompressor. like previous poster said, uncompressed video is HUMONGOUS. a codec shrinks that data to a manageable size, and unshrinks it back when playing back. (I like the suitcase analogy).

and yes it's possible to put the same audio and video data in different containers. that's what lossless transcoding does. it rips the audio and video streams, and repackages them in a different container, without any loss of quality.
Note: The resulting file may or may not be playable, depending on the container/codec support. Some companies deliberately make their codec explicitly available to work only in one or a few containers (perhaps to protect their intellectual property) - for example Sorenson Video is designed to work in MOV only. And some codecs don't work well (or at all) in some containers (for instance H.264 in AVI - supposedly uses ugly tweaks, and doesn't work all the time).

Caleb11 · 10-16-2009, 10:23 AM

hm! these info are really helpful.

what about the quality of data, does it depend on the codec or on the file format?

**blah789** · 10-16-2009, 04:55 PM

almost entirely on codec. that's what affects the compression-to-quality ratio of the audio and video streams. container's just a wrapper (like the wrapping around your xmas presents).
you can sometimes hear about raw stream dump. that's when a programmer grabs a stream out of a media file and puts it in another file, but doesn't wrap it in any container. it'll just be raw data (could be audio or video), but it hasn't been packaged.
if it helps, you can think of one of the main roles of the container is to synchronize things. it makes sure the video, audio, (and maybe subtitle) streams are played with correct timing (could be multiple audio streams in various languages, such as in your VOB files on DVD's).

however as mentioned, sometimes you can't put certain codecs in certain containers (or with great difficulty, or without playable results)

sometimes the choice comes down to portability (can you play the file format/container on a windows, a mac, or a unix machine)

some containers are better for streaming, but may contain more overhead because of that. others are leaner. others can contain just about anything you can put into them, including the kitchen sink (matroska/mkv).

10-15-2009, 12:40 PM	#1 (permalink)
Caleb11 Registered User Join Date: Jul 2009 Location: pampanga, Philippines Posts: 31 OS: win xp sp3	codec vs file format hi, what is the difference of codec and file format? i know the basic but it's not enough to understand the two. thanks. __________________ I just want to learn computer. Please help me. All i can return is "thank".

10-15-2009, 07:37 PM	#2 (permalink)
ebackhus Manager, Design Join Date: Apr 2005 Location: SATX Posts: 14,236 OS: WinXP Pro SP3/Windows 7 RTM My System Blog Entries: 28	Re: codec vs file format Say you have a file called funny.avi. AVI is the container format, but does not dictate what codec was used. H264, XviD, and many other codecs could have been used to create the file. __________________ ----------------------------- There are no dumb questions, unless a customer is asking them. Help in the fight against cancer and other serious illnesses.

10-15-2009, 10:14 PM	#3 (permalink)
zuluclayman Design Team Member Join Date: Dec 2005 Location: Newcastle, Australia Posts: 3,049 OS: Windows Vista Home Premium My System	Re: codec vs file format to expand a little on what Koala says - the file format tells you which type of container the file uses as a transport medium. This may be avi (Audio Video Interleaved) or .mpg, .mov etc. This determines the way the information is stored and delivered. The codec (Compression Decompression) is the algorithms used to firstly compress the video information then as you want to play it to decompress the information - a little bit like going on holidays - you get your clothes, squash them down to fit in your suitcase down then unpack again. Video files (and to a much lesser extent audio files) are huge if uncompressed - just imagine how much information is needed to describe the position, colour, size etc of every pixel for every frame of a video! then add the audio stream and you would have massive file sizes, making it almost impossible to store and/or transport (either to have as portable files or as in streaming or downloading from the net) these files. Codecs, to a large extent, determine the file size end quality of the video you watch. If some of the older codecs are used they will not have been able to bring the file size down and retain quality. The newer codecs such as xVid, DivX, H.264 are able to bring file sizes down dramatically while keeping fairly high quality video - this allows us to store, transport, stream and download high quality video much, much more easily than ever before. Hope this helps __________________ AutoGordianKnot Audacity K-Lite codec pack Irfan View GSpot TSF Photographer's Corner

10-16-2009, 04:01 AM	#4 (permalink)
blah789 TSF Enthusiast Join Date: Aug 2008 Posts: 2,284 OS: Windows 2000 SP4 and Windows XP SP3	Re: codec vs file format container = wrapper (file format) inside it you can have various streams (usually audio and video, but you could have multiple audio streams (diff languages), subtitles, or other kind of streams) codec = compressor-decompressor. like previous poster said, uncompressed video is HUMONGOUS. a codec shrinks that data to a manageable size, and unshrinks it back when playing back. (I like the suitcase analogy). and yes it's possible to put the same audio and video data in different containers. that's what lossless transcoding does. it rips the audio and video streams, and repackages them in a different container, without any loss of quality. Note: The resulting file may or may not be playable, depending on the container/codec support. Some companies deliberately make their codec explicitly available to work only in one or a few containers (perhaps to protect their intellectual property) - for example Sorenson Video is designed to work in MOV only. And some codecs don't work well (or at all) in some containers (for instance H.264 in AVI - supposedly uses ugly tweaks, and doesn't work all the time).

10-16-2009, 10:23 AM	#5 (permalink)
Caleb11 Registered User Join Date: Jul 2009 Location: pampanga, Philippines Posts: 31 OS: win xp sp3	Re: codec vs file format hm! these info are really helpful. what about the quality of data, does it depend on the codec or on the file format? __________________ I just want to learn computer. Please help me. All i can return is "thank".

10-16-2009, 04:55 PM	#6 (permalink)
blah789 TSF Enthusiast Join Date: Aug 2008 Posts: 2,284 OS: Windows 2000 SP4 and Windows XP SP3	Re: codec vs file format almost entirely on codec. that's what affects the compression-to-quality ratio of the audio and video streams. container's just a wrapper (like the wrapping around your xmas presents). you can sometimes hear about raw stream dump. that's when a programmer grabs a stream out of a media file and puts it in another file, but doesn't wrap it in any container. it'll just be raw data (could be audio or video), but it hasn't been packaged. if it helps, you can think of one of the main roles of the container is to synchronize things. it makes sure the video, audio, (and maybe subtitle) streams are played with correct timing (could be multiple audio streams in various languages, such as in your VOB files on DVD's). however as mentioned, sometimes you can't put certain codecs in certain containers (or with great difficulty, or without playable results) sometimes the choice comes down to portability (can you play the file format/container on a windows, a mac, or a unix machine) some containers are better for streaming, but may contain more overhead because of that. others are leaner. others can contain just about anything you can put into them, including the kitchen sink (matroska/mkv).