A webpage is not always broken because of a large mistake. Small details can produce exactly this problem: debugging: media source format is unsupported. This guide shows you what to look for, a concrete fix, and how to check that it worked.
The Idea in Plain English
Media containers and codecs are not universally supported; the browser tries supplied source elements in order.
You can test this using a small local HTML file. Change one part at a time and check the result in the browser before adding more code.
A Working Example
The first part shows a problem. The second part shows a safer or more accurate version. Compare them before reading the explanation.
<!-- Problem -->
<video controls><source src="movie.unknown"></video>
<!-- Corrected example -->
<video controls>
<source src="movie.webm" type="video/webm">
<source src="movie.mp4" type="video/mp4">
Video playback is unavailable.
</video>What Each Part Does
- The video element provides a video player when a compatible source exists.
- A source offers an alternative file for a media element or picture.
- src points to the asset the browser should load.
- type chooses the relevant kind of script, input, media or embedded object.
Before the fix, the browser can behave incorrectly or report a warning. After the change, test the exact failure rather than assuming the page is fixed.
Try It Yourself
Open DevTools Network to check whether each media resource downloads successfully.
Common Beginner Mistakes
- Check the underlying cause before changing unrelated tags.
- Changing several parts of the example at once, making it difficult to see which part caused a different result.
- Choosing a tag only because its default appearance looks right, without checking whether it describes the content correctly.
Key Takeaways
- Media containers and codecs are not universally supported; the browser tries supplied source elements in order.
- Before the fix, the browser can behave incorrectly or report a warning. After the change, test the exact failure rather than assuming the page is fixed.
- Test the markup in a browser, and check accessibility and real-world behavior where relevant.