3 files changed, 51 insertions, 42 deletions

diff --git a/audio/filter/af_scaletempo2.c b/audio/filter/af_scaletempo2.c
index cf74e6504f..0dc0a974d4 100644
--- a/audio/filter/af_scaletempo2.c
+++ b/audio/filter/af_scaletempo2.c
@@ -29,7 +29,7 @@ static void process(struct mp_filter *f)
         return;
 
     while (!p->initialized || !p->pending ||
-           !mp_scaletempo2_frames_available(&p->data))
+           !mp_scaletempo2_frames_available(&p->data, p->speed))
     {
         bool eof = false;
         if (!p->pending || !mp_aframe_get_size(p->pending)) {
@@ -65,12 +65,12 @@ static void process(struct mp_filter *f)
             int frame_size = mp_aframe_get_size(p->pending);
             uint8_t **planes = mp_aframe_get_data_ro(p->pending);
             int read = mp_scaletempo2_fill_input_buffer(&p->data,
-                planes, frame_size, final);
+                planes, frame_size, final, p->speed);
             mp_aframe_skip_samples(p->pending, read);
         }
         p->sent_final |= final;
 
-        if (mp_scaletempo2_frames_available(&p->data)) {
+        if (mp_scaletempo2_frames_available(&p->data, p->speed)) {
             if (eof) {
                 mp_pin_out_repeat_eof(p->in_pin); // drain more next time
             }
@@ -89,7 +89,7 @@ static void process(struct mp_filter *f)
     }
 
     assert(p->pending);
-    if (mp_scaletempo2_frames_available(&p->data)) {
+    if (mp_scaletempo2_frames_available(&p->data, p->speed)) {
         struct mp_aframe *out = mp_aframe_new_ref(p->cur_format);
         int out_samples = p->data.ola_hop_size;
         if (mp_aframe_pool_allocate(p->out_pool, out, out_samples) < 0) {
diff --git a/audio/filter/af_scaletempo2_internals.c b/audio/filter/af_scaletempo2_internals.c
index a4ef710319..5597d531b0 100644
--- a/audio/filter/af_scaletempo2_internals.c
+++ b/audio/filter/af_scaletempo2_internals.c
@@ -450,18 +450,31 @@ static int write_completed_frames_to(struct mp_scaletempo2 *p,
     return rendered_frames;
 }
 
-static bool can_perform_wsola(struct mp_scaletempo2 *p)
+// next output_time for the given playback_rate
+static double get_updated_time(struct mp_scaletempo2 *p, double playback_rate)
 {
-    return p->target_block_index + p->ola_window_size <= p->input_buffer_frames
-        && p->search_block_index + p->search_block_size <= p->input_buffer_frames;
+    return p->output_time + p->ola_hop_size * playback_rate;
+}
+
+// search_block_index for the given output_time
+static int get_search_block_index(struct mp_scaletempo2 *p, double output_time)
+{
+    return (int)(output_time - p->search_block_center_offset + 0.5);
 }
 
 // number of frames needed until a wsola iteration can be performed
-static int frames_needed(struct mp_scaletempo2 *p)
+static int frames_needed(struct mp_scaletempo2 *p, double playback_rate)
 {
+    int search_block_index =
+        get_search_block_index(p, get_updated_time(p, playback_rate));
     return MPMAX(0, MPMAX(
         p->target_block_index + p->ola_window_size - p->input_buffer_frames,
-        p->search_block_index + p->search_block_size - p->input_buffer_frames));
+        search_block_index + p->search_block_size - p->input_buffer_frames));
+}
+
+static bool can_perform_wsola(struct mp_scaletempo2 *p, double playback_rate)
+{
+    return frames_needed(p, playback_rate) <= 0;
 }
 
 static void resize_input_buffer(struct mp_scaletempo2 *p, int size)
@@ -471,9 +484,9 @@ static void resize_input_buffer(struct mp_scaletempo2 *p, int size)
 }
 
 int mp_scaletempo2_fill_input_buffer(struct mp_scaletempo2 *p,
-    uint8_t **planes, int frame_size, bool final)
+    uint8_t **planes, int frame_size, bool final, double playback_rate)
 {
-    int needed = frames_needed(p);
+    int needed = frames_needed(p, playback_rate);
     int read = MPMIN(needed, frame_size);
     int total_fill = final ? needed : read;
     if (total_fill == 0) return 0;
@@ -581,17 +594,13 @@ static void get_optimal_block(struct mp_scaletempo2 *p)
     p->target_block_index = optimal_index + p->ola_hop_size;
 }
 
-static void update_output_time(struct mp_scaletempo2 *p,
-    float playback_rate, double time_change)
+static void set_output_time(struct mp_scaletempo2 *p, double output_time)
 {
-    p->output_time += time_change;
-    // Center of the search region, in frames.
-    int search_block_center_index = (int)(p->output_time * playback_rate + 0.5);
-    p->search_block_index = search_block_center_index
-        - p->search_block_center_offset;
+    p->output_time = output_time;
+    p->search_block_index = get_search_block_index(p, output_time);
 }
 
-static void remove_old_input_frames(struct mp_scaletempo2 *p, float playback_rate)
+static void remove_old_input_frames(struct mp_scaletempo2 *p)
 {
     const int earliest_used_index = MPMIN(
         p->target_block_index, p->search_block_index);
@@ -601,19 +610,21 @@ static void remove_old_input_frames(struct mp_scaletempo2 *p, float playback_rat
     // Remove frames from input and adjust indices accordingly.
     seek_buffer(p, earliest_used_index);
     p->target_block_index -= earliest_used_index;
-
-    // Adjust output index.
-    double output_time_change = ((double) earliest_used_index) / playback_rate;
-    assert(p->output_time >= output_time_change);
-    update_output_time(p, playback_rate, -output_time_change);
+    p->output_time -= earliest_used_index;
+    p->search_block_index -= earliest_used_index;
 }
 
-static bool run_one_wsola_iteration(struct mp_scaletempo2 *p, float playback_rate)
+static bool run_one_wsola_iteration(struct mp_scaletempo2 *p, double playback_rate)
 {
-    if (!can_perform_wsola(p)){
+    if (!can_perform_wsola(p, playback_rate)) {
         return false;
     }
 
+    set_output_time(p, get_updated_time(p, playback_rate));
+    remove_old_input_frames(p);
+
+    assert(p->search_block_index + p->search_block_size <= p->input_buffer_frames);
+
     get_optimal_block(p);
 
     // Overlap-and-add.
@@ -638,8 +649,6 @@ static bool run_one_wsola_iteration(struct mp_scaletempo2 *p, float playback_rat
 
     p->num_complete_frames += p->ola_hop_size;
     p->wsola_output_started = true;
-    update_output_time(p, playback_rate, p->ola_hop_size);
-    remove_old_input_frames(p, playback_rate);
     return true;
 }
 
@@ -656,7 +665,7 @@ static int read_input_buffer(struct mp_scaletempo2 *p, int dest_size, float **de
 }
 
 int mp_scaletempo2_fill_buffer(struct mp_scaletempo2 *p,
-    float **dest, int dest_size, float playback_rate)
+    float **dest, int dest_size, double playback_rate)
 {
     if (playback_rate == 0) return 0;
 
@@ -712,9 +721,9 @@ double mp_scaletempo2_get_latency(struct mp_scaletempo2 *p, double playback_rate
         + p->num_complete_frames * playback_rate;
 }
 
-bool mp_scaletempo2_frames_available(struct mp_scaletempo2 *p)
+bool mp_scaletempo2_frames_available(struct mp_scaletempo2 *p, double playback_rate)
 {
-    return can_perform_wsola(p) || p->num_complete_frames > 0;
+    return can_perform_wsola(p, playback_rate) || p->num_complete_frames > 0;
 }
 
 void mp_scaletempo2_destroy(struct mp_scaletempo2 *p)
diff --git a/audio/filter/af_scaletempo2_internals.h b/audio/filter/af_scaletempo2_internals.h
index 64f4104019..f1b74ec64f 100644
--- a/audio/filter/af_scaletempo2_internals.h
+++ b/audio/filter/af_scaletempo2_internals.h
@@ -53,14 +53,14 @@ struct mp_scaletempo2 {
     int samples_per_second;
     // If muted, keep track of partial frames that should have been skipped over.
     double muted_partial_frame;
-    // Book keeping of the current time of generated audio, in frames. This
-    // should be appropriately updated when out samples are generated, regardless
-    // of whether we push samples out when fill_buffer() is called or we store
-    // audio in |wsola_output| for the subsequent calls to fill_buffer().
-    // Furthermore, if samples from |audio_buffer| are evicted then this
-    // member variable should be updated based on |playback_rate|.
-    // Note that this member should be updated ONLY by calling update_output_time(),
-    // so that |search_block_index| is update accordingly.
+    // Book keeping of the current time of generated audio, in frames.
+    // Corresponds to the center of |search_block|. This is increased in
+    // intervals of |ola_hop_size| multiplied by the current playback_rate,
+    // for every WSOLA iteration. This tracks the number of advanced frames as
+    // a double to achieve accurate playback rates beyond the integer precision
+    // of |search_block_index|.
+    // Needs to be adjusted like any other index when frames are evicted from
+    // |input_buffer|.
     double output_time;
     // The offset of the center frame of |search_block| w.r.t. its first frame.
     int search_block_center_offset;
@@ -119,7 +119,7 @@ void mp_scaletempo2_reset(struct mp_scaletempo2 *p);
 void mp_scaletempo2_init(struct mp_scaletempo2 *p, int channels, int rate);
 double mp_scaletempo2_get_latency(struct mp_scaletempo2 *p, double playback_rate);
 int mp_scaletempo2_fill_input_buffer(struct mp_scaletempo2 *p,
-    uint8_t **planes, int frame_size, bool final);
+    uint8_t **planes, int frame_size, bool final, double playback_rate);
 int mp_scaletempo2_fill_buffer(struct mp_scaletempo2 *p,
-    float **dest, int dest_size, float playback_rate);
-bool mp_scaletempo2_frames_available(struct mp_scaletempo2 *p);
+    float **dest, int dest_size, double playback_rate);
+bool mp_scaletempo2_frames_available(struct mp_scaletempo2 *p, double playback_rate);