Get a decent host
Ask the provider. Server errors, if you have access usually are in /errors/error.log if you do not have access you need to ask support.
If you mean the logs of WSC / WCF they are usually in the folder /wcf/logs
If you mean the logs of WSC / WCF they are usually in the folder /wcf/logs
I don't see a wcf folder on my server.
In public_html I have a log folder and the only thing in it is a .htaccess file.
I don't see a wcf folder on my server.
He must be running an older version that uses the WCF folder. What you see is correct, and if there's no other files inside it then you have no logs created. Which you can check anyway from the Admin CP under logs to see if any have been generated.
Might be a mod you installed causing it
You have no mods installed then. Must be your server host at fault.
I doubt it.
Why do you doubt it? You are running stock apps. So what else can it be besides your host and or maybe a bad install gone wrong.
Can you upload the same video using a desktop PC, not a mobile device. Maybe it has something to do with the video itself you're trying to upload.
Best way to find out would be to simply consult the logs.
Best way to find out would be to simply consult the logs.
Yes but I can't find any.
The forums are for user-to-user support. If you want an answer from a WoltLab employee, you should use the ticket system. That being said, sunday is not a business day.
But yeah, they will likely also ask you for the logs, so make sure to check the logs 
Yes but I can't find any.
Then consult your hoster where to find them. Somewhere in your hosters documentation this has to be described. Logs are essential, and every hoster I know offers easy access to them.
But you do realize its sunday ?
Anyway, check if you have entrys in your acp wcf logs and if not you need to ask your hoster for the php error logs.
I've got no f-ing idea, that's the reason for this thread. If someone from WoltLab would reply (like someone from XF or IPS would have by now) I could figure it out. It probably is something with my server but I can't tell my host what to look for without a reply from WoltLab staff here. I guess I'll have to create a support ticket and wait.
Paul, how big is the video. It may be that your server has a max-upload limit set smaller than the video size you're trying to upload.
If you have access to cPanel, or whatever is used, and can see PHP settings like max-upload. Then look at these two setting that might be stopping it. Even I can change them on Shared Hosting if they are too small for you causing the problem. You should be able to change them also, as max-upload might be set to a default of 2mb for you
It's tiny, 19.7 MB.
Could still be more than enough to exceed the limit. The default (!) limits of PHP are 2 MB per file and 8 MB in total per Request.
And yes, it is extremly common to see hosters still using these garbage default values today.
I have just made some changes to mine now, I wasn't aware that some have to be set bigger than others like you said. If you make changes to the max-upload file size. I had max-post size set smaller than max-upload size.
It is common for them to use stock PHP settings. When I switch from PHP 5.6 to 7.2 in cPanel. Max upload was set at default 2mb for PHP 7.2 and stopped me from installing the FileBase app until I changed it. While PHP 5.6 is set at 128mb for the same thing. So he should check those settings with his host
Could still be more than enough to exceed the limit. The default (!) limits of PHP are 2 MB per file and 8 MB in total per Request.
- upload_max_filesize - The maximum size per file. (default: 2M)
- post_max_size - Maximum size of data per request, must be larger than upload_max_filesize. (default 8M)
- memory_limit - The maximum amount of memory that PHP may consume, this must be larger than post_max_size. (default 128M)
And yes, it is extremly common to see hosters still using these garbage default values today.
Alexander Ebert what would you recommend these values be?
