Seeking general codec explanation

[stevie1877]

I have been converting avi files to MPEG-2 format for some time now, but have never really understood the codec aspect of things. I use GSpot to identify that the correct codec is installed, but how do I know what codec is actually being used during the conversion/encoding, when GSpot says more than one suitable codec is installed? I prefer MainConcept MPEG Encoder as it's fast. It allows you to enable / disable import modules such as DirectShow, but I have no idea what this actually means. How does this relate to the codecs you have installed? Can anyone explain. Apologies if this is explained elsewhere but I can't find any guides that cover codec installation in this level of detail. The reason I ask is that now and again I have an avi file that plays perfectly in WMPlayer but then the encoded MPEG-2 is flawed and I don't know why.

Many thanks

[celtic_druid]

If directshow is disabled then it will use a VfW decoder. With VfW if there is a codec registered for the fourCC (say XVID) then it will always be used. If there is nothing registered then it will go through the other registered codecs untill one accepts. Basically whatever VDub uses it will use.

Directshow works on a priority (merit) system. Whatever filter has the highest merit and is capable of joining the filter chain is used. This should be the same as whatever wmp and other dshow players use. If you want to make sure that something is used; increase its merit.

[Gurm]

It could be that the file that plays fine in WMP but doesn't encode properly is flawed in some way. There are tutorials here and at Doom9 on using VirtualDub to find errors in AVI files.

I've discovered that a LOT of people on the net seem incapable of properly encoding an AVI. I sometimes (yeah, Adam - I know it's "wrong") pull an episode of a TV show that we missed (even the DVR box isn't perfect), and inevitably the file is encoded with borked VBR MP3. I don't know why this happens - perhaps there's some widespread pirated or freeware MP3 encoder that utterly screws up VBR encoding, but at any rate EVERY tv episode I've ever downloaded was encoded this way. It's disconcerting, really.

There are a LOT of broken AVI's out there. The first step in any encode of an AVI from an unknown source, for me, is to run it through VDub and make sure it's ok, demux it, convert the audio... and then give Mainconcept or whatever encoder I'm using nice clean separate A/V streams to work with.