UserAgent: Mozilla/5.0 (Windows NT 6.1; rv:56.0) Gecko/20100101 Firefox/56.0

Steps to reproduce the problem:
1. go to https://3dthis.com/bugs/videoblob.htm 
2. hit "TEST IT" to start a 10s canvas recording
3. Play the video

What is the expected behavior?
The video cursor should move while playing

What went wrong?
The video cursor doesn't move 1st time video is played

Did this work before? No 

Does this work in other browsers? N/A

Chrome version: 63.0.3230  Channel: dev
OS Version: 6.1 (Windows 7, Windows Server 2008 R2)
Flash Version: 

I believe it's because of missing/invalid duration in the webm video generated by MediaRecorder.
It's a minor cosmetic bug, but it has other consequences like not being able to directly convert webm files with ffmpeg.
Also, a very nice move would be to support video/mp4 with MediaRecorder!!! We have to send the webm file to the server and convert it to mp4 to be Apple compatible!
 

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