title: Tempo Stretching description: How cadence-matched music playback works, and why it is not in the current release.
Tempo Stretching
Most fitness apps that play background music either lock you to the song's original tempo or fade out awkwardly when the workout BPM changes. RhythmFit does neither — it stretches the song's tempo to match your cadence, in real time, without changing the pitch.
What you hear
The song speeds up or slows down to sit on your workout's beat, but it stays in its original key — the singer doesn't turn into a chipmunk, and a slow-down doesn't turn into a dirge. When your workout shifts BPM between phases, the music ramps smoothly to the new tempo instead of cutting or swapping tracks.
Picking a compatible track
Every rhythmic track has its own natural tempo. Tempo Stretching sounds best when your workout's BPM is reasonably close to it — stretch any song too far and vocals smear and transients start to double-hit. When bundled tracks are available, the Music Picker recommends the one whose natural tempo best fits your workout (marked with a star). If you pick something far from your workout's tempo, RhythmFit keeps the stretch within a natural-sounding range rather than chasing the beat at any cost.
What we don't do
- No Spotify integration. Spotify's SDK doesn't give apps the kind of audio access Tempo Stretching needs, and its terms don't permit tempo-shifting tracks.
- No per-block song swapping. Track changes inside a workout are jarring. We change the tempo, not the song.
- No automatic key matching. Picking a song that already lives in the right key for your training mood is up to you; we don't re-pitch to match a target.
Source compatibility
| Source | Tempo Stretching? | Notes | | ---------------- | ----------------- | -------------------------------------------------------------- | | Bundled tracks | Yes | Not included in the current release. Rhythmic tracks stretch to your cadence; ambient beds play as-is. | | Apple Music | No | Your playlists play at their original tempo alongside the workout. | | Third-party apps | No | RhythmFit shows what's playing but doesn't process it. |
See Background music for what plays today and how to pick it.