Obvious error message to replace "unknown error"

[stemy2]

Hello,

Sometimes, when i upload a video, it fails because of an "unknown error". After some testing, i discovered that it was because of another video was being transcoded, so my CPU was constantly at 100%. So i think the so-called unknown error is hiding the fact that the server doesn't have enough resources for now and that we simply have to wait until transcoding is done, it would be clearer than "unknown error".

[stemy2]

I was wrong, it is not because of a server overload, it needs a deeper investigation.

Nevertheless, the problem remains the same, it's really frustrating to be unable to post a video without knowing the reason, especially beacause it leaves no trace in the logs.

[stemy2]

I still have the message "unknown error", it seems that my problem is so specific that the PR didn't fixed it.