Can't upload video

Video upload gives error after taking full upload time goes to 99% then to an error page when uploading mp4 or m4v files well under the size limit
On safari led to a 404 page
On chrome server internal error and a 500 error while trying to use an errordocument to handle request
Running version 2.6.1

An internal server error should result in an error logged in your Apache server error log, so check there to see if anything is being logged there. If it’s Apache errors (a “white screen” with plain text), there may be an issue at a lower level than Omeka happening here.