Don't let seek make a stutter at less than unit speed

src/AudioIO.cpp

@@ -623,6 +623,9 @@ private:
          double speed = static_cast<double>(std::abs(s1 - s0)) / duration;
          bool adjustedSpeed = false;
 
+         auto minSpeed = std::min(options.minSpeed, options.maxSpeed);
+         wxASSERT(minSpeed == options.minSpeed);
+
          // May change the requested speed and duration
          if (!adjustStart && speed > options.maxSpeed)
          {
@@ -641,15 +644,20 @@ private:
             // continue at no less than maximum.  (Without this
             // the final catch-up can make a slow scrub interval
             // that drops the pitch and sounds wrong.)
-            // Trim the duration.
-            duration = std::max(0L, lrint(speed * duration / options.maxSpeed));
-            speed = options.maxSpeed;
+            minSpeed = options.maxSpeed;
             mGoal = s1;
             adjustedSpeed = true;
          }
          else
             mGoal = -1;
 
+         if (speed < minSpeed) {
+            // Trim the duration.
+            duration = std::max(0L, lrint(speed * duration / minSpeed));
+            speed = minSpeed;
+            adjustedSpeed = true;
+         }
+
          if (speed < ScrubbingOptions::MinAllowedScrubSpeed()) {
             // Mixers were set up to go only so slowly, not slower.
             // This will put a request for some silence in the work queue.

src/tracks/ui/Scrubbing.cpp

@@ -341,6 +341,7 @@ bool Scrubber::MaybeStartScrubbing(wxCoord xx)
             options.pScrubbingOptions = &mOptions;
             options.timeTrack = NULL;
             mOptions.delay = (ScrubPollInterval_ms * 0.9 / 1000.0);
+            mOptions.minSpeed = 0.0;
 #ifdef USE_TRANSCRIPTION_TOOLBAR
             if (!mAlwaysSeeking) {
                // Take the starting speed limit from the transcription toolbar,
@@ -414,6 +415,7 @@ void Scrubber::ContinueScrubbingPoll()
    bool result = false;
    if (mPaused) {
       // When paused, enqueue silent scrubs.
+      mOptions.minSpeed = 0.0;
       mOptions.maxSpeed = mMaxSpeed;
       mOptions.adjustStart = false;
       mOptions.enqueueBySpeed = true;
@@ -428,6 +430,7 @@ void Scrubber::ContinueScrubbingPoll()
          const auto lastTime = gAudioIO->GetLastTimeInScrubQueue();
          const auto delta = mLastScrubPosition - position.x;
          const double time = viewInfo.OffsetTimeByPixels(lastTime, delta);
+         mOptions.minSpeed = 0.0;
          mOptions.maxSpeed = mMaxSpeed;
          mOptions.adjustStart = true;
          mOptions.enqueueBySpeed = false;
@@ -437,6 +440,7 @@ void Scrubber::ContinueScrubbingPoll()
       else {
          const double time = viewInfo.PositionToTime(position.x, trackPanel->GetLeftOffset());
          mOptions.adjustStart = seek;
+         mOptions.minSpeed = (mDragging || !seek) ? 0.0 : 1.0;
          mOptions.maxSpeed = (mDragging || !seek) ? mMaxSpeed : 1.0;
 
          if (mSmoothScrollingScrub) {

src/tracks/ui/Scrubbing.h

@@ -40,7 +40,8 @@ struct ScrubbingOptions {
 
    double delay {};
 
-   // A limiting value for the speed of a scrub interval:
+   // Limiting values for the speed of a scrub interval:
+   double minSpeed { 0.0 };
    double maxSpeed { 1.0 };