With stream recordings enabled in Administration -> Server -> Settings, you can start a server-side recording of your H.264 streams by clicking the REC button when the stream is live:
You are free to leave the page while the recording is active. When you stop the recording, it will create a thumbnail on the server and appear in the list after a few seconds. You can then playback recordings in the browser as you please, or download them for use elsewhere. The recordings are muxed into MP4 but not re-encoded, so the exact video data received by the server is what you will see in your recording.
Note: A minimum of 8GB disk space is required to begin a recording. If you don't see a REC button, check that H.264 + AAC are the incoming stream codecs, you have enabled recordings in the Admin section, and of course that your stream is live!