Issues when reproducing MP4 while embedding two files into a page

Problem

After attaching an MP4 video and reloading the page, the file preview shows the MP4 video as an audio file.

Steps to Reproduce

1. Attach an MP4 video
2. Publish the page
3. Reload the page

Expected Results

The file preview should be displayed normally, even after reloading the page.

Actual Results

The file thumbnail isn't available, and when you click to play the video only audio is played:

Workaround

1. Embed externally hosted videos.
2. Convert the MP4 file to another format (.MOV, for example)