Normalize tempo of DJ instrumental version

src/music/render/contextmanagers.py

@@ -155,6 +155,81 @@ def mute_tracks(tracks: Collection[reapy.core.Track]) -> Iterator[None]:
         track.unmute()
 
 
+@contextlib.contextmanager
+def normalize_tempo(project: ExtendedProject) -> Iterator[None]:
+    """Normalize the tempo of the project to a single tempo, then restore the project's custom tempo markers.
+
+    Assumes the "normal" tempo of the project is whatever singular tempo is set
+    in the project's settings. Does not inspect the marker values themselves.
+
+    Saves the master track tempo envelope data to project's external state
+    storage (vs. relying on this Python program's memory), deletes the markers,
+    then sets the markers back.
+
+    H/T https://forum.cockos.com/showpost.php?p=1992179&postcount=12
+    """
+    tempo_envelope = project.master_track.envelopes[0]
+    is_undo_optional = False
+    envelope_chunk = reapy.RPR.GetEnvelopeStateChunk(  # type: ignore[attr-defined]
+        tempo_envelope, "", 999, is_undo_optional
+    )[1]
+    reapy.RPR.SetProjExtState(  # type: ignore[attr-defined]
+        project.id, "MPL_TOGGLETEMPOENV", "temptimesignenv", envelope_chunk
+    )
+
+    num_markers = project.n_tempo_markers
+    for i in range(num_markers):
+        reapy.RPR.DeleteTempoTimeSigMarker(project.id, num_markers - i - 1)  # type: ignore[attr-defined]
+
+    yield
+
+    envelope_chunk = reapy.RPR.GetProjExtState(  # type: ignore[attr-defined]
+        project.id, "MPL_TOGGLETEMPOENV", "temptimesignenv", "", 999
+    )[4]
+    reapy.RPR.SetEnvelopeStateChunk(  # type: ignore[attr-defined]
+        tempo_envelope, envelope_chunk, is_undo_optional
+    )
+
+    # TODO: why set only the last marker?
+
+    (
+        _,
+        _,
+        _,
+        timepos,
+        measurepos,
+        beatpos,
+        bpm,
+        timesig_num,
+        timesig_denom,
+        lineartempo,
+    ) = reapy.RPR.GetTempoTimeSigMarker(  # type: ignore[attr-defined]
+        project.id,
+        project.n_tempo_markers - 1,
+        999.9,
+        999,
+        999.9,
+        999.9,
+        999,
+        999,
+        False,
+    )
+
+    reapy.RPR.SetTempoTimeSigMarker(  # type: ignore[attr-defined]
+        project.id,
+        project.n_tempo_markers - 1,
+        timepos,
+        measurepos,
+        beatpos,
+        bpm,
+        timesig_num,
+        timesig_denom,
+        lineartempo,
+    )
+
+    reapy.RPR.UpdateTimeline()  # type: ignore[attr-defined]
+
+
 @contextlib.contextmanager
 def toggle_fx_for_tracks(
     tracks: Collection[reapy.core.Track], is_enabled: bool

src/music/render/process.py

@@ -33,6 +33,7 @@
     adjust_render_settings,
     avoid_fx_tails,
     mute_tracks,
+    normalize_tempo,
     toggle_fx_for_tracks,
 )
 from .result import RenderResult
@@ -166,6 +167,7 @@ async def _render_instrumental_dj(
     with (
         adjust_master_limiter_threshold(project, vocal_loudness_worth),
         mute_tracks(tracks_to_mute),
+        normalize_tempo(project),
     ):
         return await render_version(project, SongVersion.INSTRUMENTAL_DJ)
 
@@ -203,6 +205,10 @@ async def _render_stems(
         return await render_version(project, SongVersion.STEMS)
 
 
+def _has_instrumental_dj_difference(project: ExtendedProject) -> bool:
+    return bool(find_vox_tracks_to_mute(project)) or project.n_tempo_markers > 1
+
+
 class Process:
     """Encapsulate the state of rendering a Reaper project."""
 
@@ -257,7 +263,9 @@ async def process(
                 )
             )
 
-        if SongVersion.INSTRUMENTAL_DJ in versions and find_vox_tracks_to_mute(project):
+        if SongVersion.INSTRUMENTAL_DJ in versions and _has_instrumental_dj_difference(
+            project
+        ):
             results.append(
                 (
                     SongVersion.INSTRUMENTAL_DJ,
@@ -306,9 +314,10 @@ async def process(
 
             self.progress.update(task, advance=1)
 
-        if len(results):
-            # Render causes a project to have unsaved changes, no matter what. Save the user a step.
-            project.save()
+        # TODO: REVERT ME. Avoiding saves while developing experimental feature.
+        # if len(results):
+        #     # Render causes a project to have unsaved changes, no matter what. Save the user a step.
+        #     project.save()
 
     @cached_property
     def progress(self) -> rich.progress.Progress: