Uploading webm with no video stream causes "500 Internal Server Error"

[nivex]

I have a .webm test file that contains only an audio stream. This file plays correctly in browser (Firefox 60.0.1). When I upload it to Mastodon to add to a toot I get a "500 Internal Server Error"

I had an instance admin attempt to upload this test file and report the error logs. It appears to be failing on generating a thumbnail for the timeline. I suggest two potential improved outcomes:

1. Dialog reports that there was a problem processing the media.
2. Media is accepted and a blank thumbnail is displayed.

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• I searched or browsed the repo’s other issues to ensure this is not a duplicate.
• This bug happens on a tagged release and not on master (If you're a user, don't worry about this).

[nivex]

Oh dear, it seems I may not have searched well enough. This appears to be a duplicate of #6147.
I realize there is some contention about uploading audio files. This would tend to bias the fix toward my first suggestion to improve the feedback to the user.

[nivex]

Oh dear, it seems I may not have searched well enough. This appears to be a duplicate of #6147.
I realize there is some contention about uploading audio files. This would tend to bias the fix toward my first suggestion to improve the feedback to the user.