I think the point I was trying to make in my post has been better articulated by AbsoluteDestiny and others since then, so hopefully you understand my position.
People know what DivX is. Especially the average anime fan these days - they're living off all these digisubs which generally are played back with either DivX or some form of XviD. I made all my encodes to be DivX5 compatible because I figure that's what most people will already have.
Yes, I realize that MPEG1 is more universal, however at this point I think I have more viewers who would rather download a higher quailty, smaller size file because they're on slow connections as opposed to people who have computers which can't run DivX files properly. I could play my encodes on my P2 366 laptop (although Closer to God 2 was pretty hard on it), so obviously the CPU barrier of entry is very low.
But Matroska is totally different - it's a container format. And for what we're doing, it's more than we need. If I make a person install DivX, that's 1 thing they have to install. But if I put XviD in a Matroska file, now they have to install the directshow splitters PLUS the codec. I already don't like forcing people to install DivX5, I don't want to add another thing on top of it.
Back when I was first encoding, I had MPEG1 and DivX3.11 versions of all my videos on my site. They both got downloaded about equally, but the MPEG-1 downloads I found from asking people were mostly because people thought the MPEG-1 looked better, not because it was more compatible.
VicBond is 100% correct in saying that MPEG1 is the most compatible format. But the added quality and size reduction I get from XviD is worth the extra effort I make my viewers go though.
Encoding my videos in Matroska does not provide me any benefit which would persuade me to force my viewers to install it. It's great for making DVD backups or digisubs or whatever, but for AMVs, it's just not necessary.
So I wish you luck with your container format, I honestly do hope it gains a whole lot of support and becomes completely ubiquitous. THEN I will use it happily. But until then it's not in my or my viewer's best interests to switch.


