Author Topic: what does .avi stand for? (lossy .avi - lossless .avi)  (Read 10870 times)

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Offline japanesebaby

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what does .avi stand for? (lossy .avi - lossless .avi)
« on: June 23, 2008, 18:39:42 »
a conversation originally started here:
http://curefans.com/index.php/topic,5289.msg52670.html#msg52670


The original - in MPEG-2 - is a lossy codec too, hence the reason they are both of similar size.

http://en.wikipedia.org/wiki/Mpeg-2

Re-encoding to a different lossy codec is not ideal, since you're right in saying you would simply degrade it further. The usual reason is so that you can edit it, and it looks like the guy did that here. MPEG-2 is a proprietary format and most editors - like VirtualDub - won't deal with it because of infringement (although there is a mod that will).

of course, all mpeg-2 is lossy - if we wanted to share lossless videos we'd need to start sharing raw .dv/lossless .avi... talk about people's ratios sinking there haha :shock:
and sure, some programs won't edit mpeg-2, i know that well because my favorite video editor only accepts raw .avi. yet i'd say the solution is to find a program that will, instead of re-encoding it all. i mean, this is a fully edited tv broadcast anyway, not something that anyone really needed to edit any further(?).
and so, i don't see much point in converting a tv broadcast back to .avi just because someone wants to edit it - i think people simply like to convert to lossy .avi simply because they want to compress the files - thus make them look like "good" ol' youtube...
and of course, there's .avi and .avi by the way: lossy .avi and lossless .avi, as we know. but lossless .avi is something you need to have when you have something like an original analog transfer etc. - but if you are dealing with a digital tv broadcast of today (like here), you shouldn't really need .avi to anything (be it lossy or lossless). i know some people confuse editing with re-authoring and think that one always needs to re-encode in order to re-author anything. but of course that's not true at all. mpeg-2 is maybe not editable but it's fully "re-authorable" (i suppose that's not a word... :-P) any time.

so what i meant was that since all the digital broadcasts are already encoded to mpeg-2, all one needs to do is to capture that stream and author it on dvd and that's it - anything else is going to be unnecessary degradation of the quality.

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Offline MAtT

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what does .avi stand for? (lossy .avi - lossless .avi)
« Reply #1 on: June 23, 2008, 18:50:21 »
Yeah, I agree with you. It's pointless re-encoding it just to make a few edits. And anyway, as I say, both VirtualDubMod and VirtualDubMPEG-2 are still available and will handle MPEG-2 editing.

I understand what you say about AVI, but it's not strictly correct. AVI can't actually be lossy or lossless, only the encoded streams it contains. It's just a container.

http://en.wikipedia.org/wiki/AVI

Offline japanesebaby

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what does .avi stand for? (lossy .avi - lossless .avi)
« Reply #2 on: June 23, 2008, 19:31:46 »
I understand what you say about AVI, but it's not strictly correct. AVI can't actually be lossy or lossless, only the encoded streams it contains. It's just a container.

http://en.wikipedia.org/wiki/AVI

what i meant was that the label "avi" alone doesn't tell you whether something is a super-high bitrate raw capture or a low bitrate compressed file. when i say lossless .avi i mean something similar to raw .dv. and why call it lossless? because it's as lossless as you can get with video transfers, and everything else that follows is going to be more or less compressed. 

people usually think of lossy compressed divx when they hear ".avi". some dvd trading scenes use "avi sourced" as a very negative term, always stadning for a dvd that was sourced from some low bitrate (uaually web-sourced) divx files. which is of course complete crap. but any analog video transfer is actually "avi-sourced": only that it was captured as high bitrate, raw lossless .avi, then compressed to mpeg-2 (which actually made it lossy...).

so i find it often funny/sometimes sad how people think pretty much every mpeg-2 is "lossless" and all avi is "lossy", although it's pretty much the other way round: there's no such thing as lossless mpeg-2 but not all avi is compressed and lossy.
so the extension doesn't mean anything, it's the bitrates that tell the story.
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Offline MAtT

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what does .avi stand for? (lossy .avi - lossless .avi)
« Reply #3 on: June 23, 2008, 20:08:46 »
I understand and agree with what you're saying, that when you get an AVI file (and AVI files may or may not have .avi extensions) it can be good quality or bad quality compression dependent on the codec used and the bitrate, but I don't know what you mean by "any analog video transfer is actually avi-sourced".

AVI is a mulitmedia container file format, property of Microsoft and created in 1992, and is just one of a choice of containers you can use to contain your encoded streams.

For example, if you plug your video into your PC and capture the stream into - for instance - quicktime, WMV, or an MPEG codec in a matroska container, then that has nothing to do with AVI.

Do you mean "AV-Sourced", or are you just using the term AVI where you mean "AVI and any other computer format"?

Offline japanesebaby

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what does .avi stand for? (lossy .avi - lossless .avi)
« Reply #4 on: June 23, 2008, 20:43:24 »
I understand and agree with what you're saying, that when you get an AVI file (and AVI files may or may not have .avi extensions) it can be good quality or bad quality compression dependent on the codec used and the bitrate, but I don't know what you mean by "any analog video transfer is actually avi-sourced".

oops it looks like i actually accidentally skipped half a sentence there and i can see the word "any" is indeed misleading. i certainly had a more specific situation in mind than just "any" kind of transfer situation. what i had in mind there was when you do a "serious"(* video transfer from an analog source by using an analog converter and capturing that with your computer. the best way then (imo) is to capture in lossless avi stream (which you can then edit, remaster all you want and later encode to mpeg-2, in order to author it on a dvd).
so, any video that was transferred by this method is actually kind of "avi sourced". and thus to use the expression "avi sourced" as a negative expression has led some people to think that all avi is some lossy low bitrate crap and thus to be avoided altogether. i've made a lot of video transfers like this and some people have asked me "but why do you convert to .avi first?? :((", because they've thought that capturing in lossless avi means capturing in some totally silly low bitrate format (like .wmv etc.) - which is of course a misunderstanding. 


*) by "serious" i mean you really want to transfer something properly, in best possible dvd quality available to you. of course you can choose to capture in some low bitrate format too, but that's probably for some temporary purposes only, not for archiving/remastering stuff on dvd.
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Offline MAtT

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what does .avi stand for? (lossy .avi - lossless .avi)
« Reply #5 on: June 23, 2008, 20:49:47 »
Ah, I see what you mean now. The whole area of computer AV formats is a bit of a terminology and technical nightmare to be honest!

 

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