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please disable plugin: System - Pammag that plugin causing lot of error message.
how much filesize of that video? it can me time out issue. please try to incease php time out parameter again.
your issue can be timeout issue. that depend with your connection it self. please increase timeout setting at php cofiguration.
also please try to set joomla error reporting to none, to hide that error message. video upload using ajax, any error/warning messages can be interrupted any process.
if still cant, try to turned off pammag plugin and try to upload that video again.