[badtz]

http://www.insaneness.com/ac3.html

Is that still necessary to install? If so, should you still install it w/the QT mpeg-2 component?


Also, is it necessary to install the DivX AND the XviD plug-ins?

[Jacke]

The AC3 component relies on the official DivX codec for AVI parsing, it doesn't do anything for AC3 audio in VOB/MPEG files. If you have an AVI file with AC3 audio you want to play in Quicktime you'll need the component.

You don't need both codecs, as the newest DivX codec comes with a "generic MPEG-4 decoder" that can decode most MPEG-4, but personally I find the XviD component better at playback of XviD files than the DivX codec. I don't know if you can turn off the generic MPEG-4 decoder so the DivX decoder only handles DivX video, but I think they also offer v5.1.1 for download that comes without it.

[badtz]

are there any codecs that XviD can play but not DivX?

[Thinine]

Yeah, Google for Xvid QT codec and you should find the dedicated Xvid codec for QuickTime.

[badtz]

conversely, are there codecs that DivX can play but XviD does not?

[wouldn't it be better to install both]?

[Jacke]

The DivX codec can probably play (just about) any XviD file since they're both based on MPEG-4, but depending on the options used when compressing the file, there may be places where the DivX codec wouldn't play properly. You should probably install both the DivX and XviD codecs, since the DivX codec comes with an AVI parser that allows MP3 audio in AVI files to play back correctly (but the latest version comes with the "generic MPEG-4 decoder" that automatically plays back XviD instead of the XviD codec).

You can also have a look at 3ivx, which also plays back most MPEG-4 based video formats like DivX, XviD and Apple's MPEG-4. The problem with 3ivx is that you can't choose what video formats it will play.

Personally I use all three of them, but I use version 5.1.0 for DivX (the last version to support video passthrough for encoding), the latest XviD QT component, and a modified version of 3ivx that doesn't decode XviD (but you're technically not allowed to modify it, so maybe I shouldn't have said that). This means that AVI files with MP3 audio plays correctly using the DivX AVI parser, 3ivx decodes DivX, MPEG-4 and most other MPEG-4 based video, and the XviD codec decodes the XviD video. I use 3ivx since I percieve it to be faster at decoding DivX than the official codec (though I've had some problems with a couple of XviD files).

For clarification, video formats are identified by fourCC's, a four-character code embedded in the video track; for DivX there's "DIVX", "divx", "DX40", "DX50" etc. (depending on what version was used for encoding), for XviD "XVID", "xvid". 3ivx used to have "3IVX" or "3IVD", but since version 4 they encode to the general "MPG4" which signifies pure MPEG-4 video.

Ok, this got longer than I had planned.