sopax wrote:What converting would you suggest, if not mp4?
It's not about the mp4 FORMAT, but the CODEC and/or encoding used. MP4 is definitely the most appropriate format for the web, but you must still use browser-friendly codec/encoding.
sopax wrote:It is a long video of 250MB, so it should preferably not be larger in size.
This is unrelated.
sopax wrote:My converter has no options for changing this format.
I don't know what video converter you are using of course, but either 1) It is not converting to a web-friendly format, or 2) The "Planar 4:2:0" encoding was part of the original video, and your converter does not convert this encoding to make it web-friendly. There are loads of video converter applications of course, also online converters (search "online video conversion").