I couldn't find anywhere more suitable to post this, please move it as necessary if it helps. I couldn't post a reply in the FAQs.
FLV viewer plugin: I've found that the ffdshow codecs as linked in the FAQs - [HOW TO: Enable/fix playback of various media formats in Opus) - work fine for most .FLV videos (eg YouTube) but some, because of some ID3 tag issue, only work in the viewer pane (and Windows Media Player) if you register the version 1.0.0.5, 408k-sized FLV splitter as supplied in the Klite v5 pack and attached below - so install the ffdshow pack, then either register the attachment manually, or when you install KLite, deselect everything but FLV splitter (flvsplitter.ax). (The Klite codecs seemed to mess up playing .ASF videos for me). I've no idea whether this is a 32/64-bit issue or what, it just works.
Hope this helps somebody - and shows up in an FLV plugin search:)
FLVSplitter.zip (184 KB)