AVI vs. Divx format

[fwang2]

Hi,

I am a bit confused by these two formats. AVI video quality is said (on the newbie guide of this site) to be inferior than Divx, and to my understanding, it is not being developed by Microsoft anymore.

At least two conversion guide I read on this site said, to use VirtualDub to convert a DVD to divx, you must first get it into AVI format -- I have sucessfully done this, but it doesn't quite make sense if AVI quality is no good as Divx. However, I must say I could not tell the difference when I play both format on my computer. Any idea?

A more general question is, if I want to archive some DVD video clips, which may later burned on to DVD or SVCD/XVCD, which middle format gives me the best balance on video quality and compression rate (for saving disk space)?

Thanks for the help.

Oliver

[fwang2]

Sometimes, I have also read "Save it as Divx avi", that gives me the impression that avi is one of divx format, exactly what is the relationship between these two?

oliver

[vitualis]

AVI is basically like a wrapper. It puts elemental video and audio together in a standardised way so that you have digital video on the PC.

AVI doesn't say HOW the video and audio need to be encoded/compressed if at all.

DivX is a compression method for video and you can use it as an AVI codec (compression/decompression).

That is, the video is compressed using the DivX codec (which is a type of MPEG-4) and it is saved as an AVI file with the audio.

Regards.

[gll99]

Avi is a structure (or container) for storing and retrieving Audio Video data.

The format allows you to store other information describing the video and audio, a second audio track, and other proprietary information. Some of this is stored automatically when the file is created.

The format called avi allows for the data to be stored uncompressed (which takes a lot of space) or to be compressed using any number of codecs or compressors so that the video (or audio) data will take less space in the file.

Mpeg4 is one such video codec developped by microsoft but because it is owned by microsoft no-one knew exactly how it compressed video so no-one could change it or improve it. Finally someone broke (or cracked) the code and recompiled a changed codec and called it DIVX. Many changes have been made since then but from the the mpeg4 codec many have sprung up divx3, divx4 and xvid are just a few of them.

There are many other codecs like that but using different compression mathematics. Some are truer to the original image than others and some
compress more than others. There is a large choice of codecs (compressor/decompressor) available.

The audio too can be compressed inside the avi. One popular compressor you know of is Mp3. Mp3 files can be on their own but the codec can also be used to compress audio in an avi to make the file smaller.

This may repeat or confirm what's already been said but sometimes seeing it expressed in a different manner helps.

[vitualis]

Just some interesting errata...

MPEG-4 wasn't developed by Microsoft, but Microsoft created an MPEG-4 based codec (for example, Cadbury's didn't invent chocolate, but it makes a type of chocolate).

They restricted it to be only able to do certain things. Someone then came along an cracked it (no recompiling took place), and allowed it to be used as an AVI codec in a much more flexible way. This is what came to be known as DivX;-) 3.11.

Hence, DivX;-) 3.11 is intrinsically illegal.

Obviously, this root in pirarcy (especially from Microsoft of all companies) became untenable for those who desired legitimacy so there was a move to make an open source / free MPEG-4 codec as good as the Microsoft codec (Project Mayo).

My interest in DivX waned at this particular time so I can't tell you entirely what happened (perhaps someone else can continue the story), but DivX4 and DivX5 (which were based on Microsoft free code) were released and at sometime, it was no longer open source and became commercial.

There is still an open source MPEG-4 codec project in continuation -- XviD.

Regards.

[fwang2]

Thanks, Michael and gll99, both of your comments are extremely helpful and clarified quite a few things on my mind.

I wonder if you have any comments on which format you would use for archiving purpose? (My way of conversion (dvd2avi, then generate a fake avi, then virtualdub it as divx ) has audio synchronization problems, I am not sure that is the way to go.

Regards,

Oliver