Dear arggg14 and chabig, thank you for your suggestion but I just wanted to only use Quicktime Player for all my video files rather than using many players. I am using VLC player only for .flv files for long time. Perian is supported before and it was working without any problem in Snow Leopard and I always used to use Quicktime Player for .flv files. Now, it seems to be the problem in Yosemite as I have recently upgraded.
Anyway thank u for your time and suggestion.
I have the latest version of Perian also, and it seems to no longer convert flv. As Perian is no longer supported, it only makes sense that at some point it will probably stop working. You should avoid flv video, and if you have some that you want to keep, look for ways to convert them to mp4. There are many apps that claim to convert. http://www.macupdate.com/find/mac/flv
Hi Chabig, thanks for your reply. Sometimes, I download flash videos and I have to deal with .flv files or else mostly I use .mp4. As u suggested I have been using video converters like Handbrake to convert my .flv videos to .mp4, which is quite good. Anyway, thank u.