I agree that it would be nice to be able to play Flash videos, and even interactive Flash content in SL. I think that this support will come if/when we have a more integrated and compatible web browser in-world. Quicktime, and the SL client, actually used to play some Flash videos but Apple removed that capability in recent updates - not sure why.
If I'm not mistaken, the Flash Video format (FLV) is really just a wrapper for other video codecs - just like Quicktime. Each format has a list of audio/video codecs that they support, like Sorensen, h.264, etc. I'm sure that each format has it's strengths and weaknesses, but Quicktime does support a much wider range of codecs - including nearly all of the codecs supported by FLV.
Here's a list of codecs supported by Quicktime:
http://www.isholf.is/klipklap/quicktime/And a Wiki entry that details the codecs supported by FLV:
http://en.wikipedia.org/wiki/Flash_VideoI'll admit to being a bit of a Quicktime fanboy, but I would like to respond to some of the things mentioned in this thread.
"Well FLV streams better than Quicktime. Quicktime is a lot slower to start playing and needs a bigger chunk in its buffer."
I disagree. A properly formatted quicktime file can begin playing almost immediately - especially one that will work well in SL.
"Now, FLV may not be natively supported but just about every website under the sun uses it and you know why? Because it beats Quicktime and MP4 when it comes to streaming and file size."
My guess as to why Flash video is so common? A higher percentage of people had a Flash player installed in their browsers as video became popular on the Web. And since both formats support similar codecs I see no reason why Flash is a superior format. For instance H.264, an extremely efficient codec, is the same no matter what wrapper it is in. The visual quality and file size will depend on the settings used when encoding.
"BUT the supported movies are MUCH too limited."
Quicktime has supports dozens of different codecs and formats. See the link above for a list. Quicktime is not just .mov files: it also supports mp4, avi, mpg, 3gp, etc.
"Quicktime is outdated and is no longer used by any site"
Not true. Quicktime is as relevant and useful as ever. It's used on many sights, especially when video quality is important. It's supported by every video sharing site that I have ever used, and a lot of times it is the preferred upload format on these sites. Even on a site like Pond5, a high quality stock video footage store, Quicktime is the only supported format.