Merge pull request #4682 from Holzhaus/enginebuffer-setlocalbpm-debug…

…-assert-fix

EngineBuffer: Fix assert when new track is loaded during playback with sync

src/engine/enginebuffer.cpp

@@ -1304,18 +1304,22 @@ void EngineBuffer::postProcess(const int iBufferSize) {
     }
     const mixxx::Bpm localBpm = m_pBpmControl->updateLocalBpm();
     double beatDistance = m_pBpmControl->updateBeatDistance();
-    // FIXME: Double check if calling setLocalBpm with an invalid value is correct and intended.
-    mixxx::Bpm newLocalBpm;
+    const SyncMode mode = m_pSyncControl->getSyncMode();
     if (localBpm.isValid()) {
-        newLocalBpm = localBpm;
-    }
-    m_pSyncControl->setLocalBpm(newLocalBpm);
-    SyncMode mode = m_pSyncControl->getSyncMode();
-    m_pSyncControl->reportPlayerSpeed(m_speed_old, m_scratching_old);
-    if (isLeader(mode)) {
-        m_pEngineSync->notifyBeatDistanceChanged(m_pSyncControl, beatDistance);
-    } else if (isFollower(mode)) {
-        m_pSyncControl->updateTargetBeatDistance();
+        m_pSyncControl->setLocalBpm(localBpm);
+        m_pSyncControl->reportPlayerSpeed(m_speed_old, m_scratching_old);
+        if (isLeader(mode)) {
+            m_pEngineSync->notifyBeatDistanceChanged(m_pSyncControl, beatDistance);
+        } else if (isFollower(mode)) {
+            m_pSyncControl->updateTargetBeatDistance();
+        }
+    } else if (mode == SyncMode::LeaderSoft) {
+        // If this channel has been automatically chosen to be the leader but
+        // no BPM is available, another channel may take over leadership and
+        // this channel becomes a follower. This may happen if the track is
+        // analyzed upon load and avoids sudden tempo jumps on the other deck
+        // while the analysis is still running.
+        requestSyncMode(SyncMode::Follower);
     }
 
     // Update all the indicators that EngineBuffer publishes to allow