Starting playback on an audio or video file from a specific point in time is supported out of the box, by all major browsers (except iOS/WebKit*). You do not even need Replayer for that.
Since 2012, there is a W3C specification recommendation for Media Fragments. The specification proposes a way to restrict the media resource presentation in the client to a subset of the complete media resource. While the specification mentions temporal, spacial, track and id dimensions, the ability to set an offset time for playback is the most interesting part.
The media fragments work by adding an URI fragment with a dimension identifier and one or more values. E.g. with #t=x, the playback starts at x seconds in.
Consider the following 144 seconds long video:
Video showing a free return trip around the moon. (Credit: NASA's Goddard Space Flight Center)
Setting the start time:
https://lib.replayer.app/nasa-4k/13537_Apollo13ViewsMoon4K_YouTube4K.mp4#t=122.35
You can also set an end time, with a separating comma. The video automatically stops at the end time:
https://lib.replayer.app/nasa-4k/13537_Apollo13ViewsMoon4K_YouTube4K.mp4#t=122.35,124.081
It's also possible to use the h:mm:ss.z notation (note that minutes and seconds are required to be in two digits):
https://lib.replayer.app/nasa-4k/13537_Apollo13ViewsMoon4K_YouTube4K.mp4#t=02:02.350,02:04.081
You do not need Replayer to create and use the above examples. Unfortunately however, no further annotation of these start and end times are possible this way. Also, looping of these fragments is not implemented. With Replayer, you can create cues with names and further annotations. Various loop modes are supported.
Use annotated cues with Replayer (in the browser)
iOS with the WebKit browser engine does not support media fragments (or fragments at all) when using blobs from the device's storage (e.g. from IndexedDB or WebSQL) up to the most current iOS version (17.3 as of today). It seems to be a longstanding issue and has risen more than one question on Stackoverflow.