This is related to the bugs raised here: https://jira.atlassian.com/browse/CONF-23169 and here: https://jira.atlassian.com/browse/CONF-26563 , which is tracked here: https://jira.atlassian.com/browse/CONF-19524 . The multimedia macro does not render videos in iOS' Safari, with a crossed out play button.
This is reproducible in Confluence 4.3 and up (even 5.x). The umbrella issue (
CONF-19524) is resolved in 4.3, but I think the resolution is related more to support for iOS for regular Confluence view functions, not comprising of video playback, hence, this bug report.