HLS (m3u8 files) will play on iOS (and some Android but support can be clunky) and Mac OS Safari in an HTML5 audio tag:
<video width="640" height="360" preload="auto" controls src="http://[ServerIP]:1935/vod/test.mp4/playlist.m3u8"></video>
RTSP can be played on Android via an a tag in Chrome:
<div id="myElement">
<a href="rtsp://[ServerIP]:1935/vod/mp4:test.mp4">watch this stream over RTSP</a>
</div>
RTSP should work in a HTML5 video tag on Android but only on the native browser (well that is my experience of it I normally use the a tag as Chrome is now the default browser in Android 4+): <video width="640" height="360" preload="auto" controls src="rtsp://[ServerIP]:1935/vod/sample.mp4">
</video>
To support desktop PC, either provide a download link to the video tag src (mp3, ogg, wav ..) or if you have to use a streaming protocol you will need to resort to a plugin like Flash (and feed it a RTMP or HDS feed).
There is the VLC plugin for web browsers that can allow playback of RTSP streams but that is in an embed tag:
<embed TYPE="application/x-vlc-plugin" autoplay="no" loop="no" width="640" height="360" target="rtsp://[ServerIP]:1935/vod/sample.mp4"></embed>
Though HTML5 video is protocol agnostic it is dependent on the web browser/OS manufacturer implementation and that can vary along time and manufacturers.