QuickLook not playing videos

Do you use OS X 10.9 Mavericks as hinted by the fact, that this thread is in the OS X 10.9 Mavericks sub-forum?
If so, which DP?
Is it your main OS or do you have OS X 10.8 Mountain Lion or earlier to fall back onto, in case the beta you use is not behaving as a final version?

 

What formats used to work aside from these?

My guess would be that you had perian installed on ML which lets quicktime handle a bunch of extra formats (avi, mkv, and flv being some of the main ones) and also quicklook (since quicklook only plays videos that quicktime supports). Perian does not work in Mavericks and it may never since there is only one more update planned before perian is discontinued -> http://perian.org/

The only solution I know of is to use 10.8 (although there might be something else I have no idea what it is). Hope that answers your question.

Edit:

You could also use VLC media player and simply batch open all the videos you want to open in a playlist. This would actually probably be faster than browsing with Finder and Quicklook. VLC can handle pretty much any video/audio format you throw at it and it runs quite well on Mavericks it's also free and open source http://www.videolan.org/vlc/index.html.

 

it's not really a bug. they completely switched over to AVfoundry for the media backbone system-wide. better than qt7 in quality and performance but of course it does not support all the formats perian and qt7 did. an interesting thing i found out in YOSEMITE: if you cannot preview a .mov in quicklook, try changing the ending to ".mp4" regardless of the format. if you have the codec installed chances are pretty good that you will see it. make sure you have the PRO APPS CODEC PACK though. perian and qt7 still work in YOSEMITE and are available for free. QTX became way better and has non of the previous interface bugs it had in MOUNTAIN LION or MAVERICKS.

 

I just tried to do what you're saying, and renamed a .mov file that wouldn't play natively to .mp4, and it still wouldn't play in quick look... this is annoying. Perian shows up as "installed" on my machine, but I don't think QuickTime uses it...?