If videos don't play in your published output, review the following reasons and solutions.
Test your published content in its intended environment. If you view published content on your local computer, you'll encounter security restrictions related to your web browser and Adobe Flash Player that may cause various features to fail. To avoid these local security restrictions, view your content in the environment for which it was published:
You may need to update Adobe Flash Player on your computer to a version that supports FLV and MP4 movies. Adobe Flash Player supports these movie formats in the following versions:
Don't use special characters, accents, or spaces in your video file names. Use only letters, numbers, underscores, and hyphens.
If FLV or MP4 videos still won't play after uploading your published content to a server, it's likely that you need to add these MIME types to the server. Here's how: