Feature request: crossfading between tracks

[tsirysndr]

Add a configurable crossfade so playback fades the outgoing track out while fading the incoming track in, eliminating the gap/hard cut between songs.

Proposed behaviour

• User-configurable crossfade duration (e.g. 0–12s) in Settings, with 0 = off (current behaviour)
• Applies to automatic track transitions in the queue; behaviour on manual skip is up for discussion (likely a quick fade rather than full crossfade)
• Should respect gapless playback for albums where crossfade is undesirable (optional "disable crossfade for gapless albums" toggle)

[MathieuDubart]

Thanks for the detailed proposal! This is planned before v2.0, with one caveat worth flagging.

The audio engine runs a single rendering engine, so a true crossfade (both tracks mixed together) isn't practical without rebuilding the playback core. Instead I'm shipping a preloaded sequential fade: the outgoing track fades out, the next track is preloaded so it starts instantly, then fades in and killing the gap/hard cut without the actual blend. It sounds best short, so:

• Duration: configurable in Settings, 0 = off, but capped shorter than 0–12s (likely ~0–5s, default ~2.7s) : long sequential fades sound like a dip, not a blend.
• Manual skip: quick ~200ms fade, not the full duration.
• Gapless: same-album consecutive tracks skip the fade, with a toggle (on by default).

In progress now, thanks for the feedback!
(keeping the issue open for further investigations post v2.0)