Minimal track length for crossfade should be configurable (now 20 secs fixed)

[jri]

Feature request

Since MPD 0.23 songs shorter than 20 seconds are not crossfaded anymore (#1184). There is no config option for this threshold and there is no possibility to get back the "old" behavior.

MPD should have a config option to adjust that value (20 secs) resp. to switch this conditional crossfade off completely (as it was before MPD 0.23).

Background: Since 5 years I run a web radio and I have quite a lot of short snippets in the program, e.g. jingles or announcements. For every track (not just the snippets) I want have the crossfades as accurate as possible, on a per-track basis, based on the actual track content (not on its length). I've solved that problem by a) configure MPD to do constant 4 sec crossfades, and b) by handcrafting each of the thousands files manually, that is adding a suitable amount of silence (0-4 sec) at the begin and/or at the end of each file. (I do this without re-encoding the audio file by the means of the Fission application.)

Recently I've updated the radio server and with the new Ubuntu 22.04 came a newer MPD (0.23.5, which I appreciate very much as serious bugs are fixed compared to my previous MPD 0.20.18). Then I realized that a lot of the snippets are now playing (due to my adjustments) with unwanted silence at the beginning and/or end. I'd love to get back the old listening experience.