Flickr Uploadr on OS X scans the folders I selected, but it doesn't count the videos in that folder. If the folder doesn't contain any photos, it simply says:
No photos
How do I get Uploadr to upload videos to Flickr?
Open the Uploadr app and click the about tab. Then click on the logo to make a hidden menu appear:
Click "Enable Video Upload" and that's it! You can now upload videos in the formats that Flickr supports.
Reference: UserVoice request about this issue