[feature request] Define functions for making mpv play the curent subtitle audio at point 25%, 50% and 75% of the audio

[rodrigomorales1]

Let me explain my use case: When I am editing a subtitle in a *.srt file, I sometimes want to check if the audio for that segment is consistent with the subtitle, to check this I am willing to listen to the entire audio for that subtitle. When editing the end time of a subtitle, I frequently want to check if the last part of the audio is consistent with the subtitle. Currently, when the end time of a subtitle changes, the audio is played from the start time, so I unwillingly need to listen to the audio starting from the beginning. I believe it would be more convenient for some users (such as me) if there were a function that would allow the user to play the audio starting at position 75%, so that the user don't need to listen to the 0%-75% segment, which the user might not be interested in listening.

In my use case, there are some subtitles which are 15 seconds long. Sometimes when I change the end time, I want to listen the last part of the audio (i.e. the segment 75%-100% in the current subtitle audio). Having to listen to a 15 seconds audio even though I'm interested in the last part is bothersome. I wish there were a function that I could map to a key to a function that makes mpv play the current subtitle audio starting at 75%.

I believe having functions that play the current subtitle audio at positions 25%, 50% and 75% would make subed more convenient to other users, because users can map those keys to a key and instruct mpv to play starting at a point that is closer to the part they are interested in listening.