Publishing as MP4 not as clear as a swf

First decide if you want an interactive eLearning course or a video. There is a significant difference between those two!

For a video (non-interactive), either use another application (Camtasia is one of the most known) or use the Video Demo that comes with Captivate and results (raw file) in a cpvc-file, not a cptx-file. It has a dedicated video editor that has some nice features but is not as many as Camtasia has.

If you want a real eLearning course (video is to me not real eLearning because of the lack of interactivity) go with a cptx-file (slide-based contrary to cpvc-file). You can publish to SWF which is the 'old' way and is only supported by desktop browsers. maybe they will even discontinue to support it. There will be a companion HTML-file to launch the SWF as has always been the case (some other files like JS and CSS as well). In that case the user needs the Flash Player to be installed. Publishing to an interactive pdf requires Flash as well, publishing to EXE is really also Flash-based.

The present way of publishing is to HTML5, which is supported (more or less, not all in the same way) by all browsers on desktop and mobile devices. You'll end up with a folder with a lot of files, and the course will be launched from an index.htm file (within that folder).

If you have to report to a LMS you need to publish as a SCO.

There is a hybrid solution where you can publish at the same time to SWF and HTML, and upload the whole bunch of files. Launching will occur with another file: multiscreen.htm and when the course is viewed, Captivate will detect which type of output it should show (depends on the device).