I use minitube it's excellent program with no problems.
First of all install community codec pack then you need to have latest flasplugin installed,best way to do that have web browser like midori installed then in appdata they should be midori folder in there is plugin folder install it in there and rename your plugin,once that's done then minitube will play videos without any problems plus i downloaded more than 20 videos from minitube program and then i played downloded videos they worked like a charm.
most time i do that with youtube they won't even download,but with minitube it's always success.