audio: add pitch-shifting feature

Uses resampling in tandem with a time-stretching audio filter to
change the audio's pitch while leaving its tempo intact.

DOCS/interface-changes/pitch-shift.txt

@@ -0,0 +1 @@
+add `--pitch` option

DOCS/man/options.rst

@@ -237,6 +237,11 @@ Playback Control
     speed higher than normal automatically inserts the ``scaletempo2`` audio
     filter.
 
+``--pitch=<0.01-100>``
+    Raise or lower the audio's pitch by the factor given as parameter. Does not
+    affect playback speed. Playing with an altered pitch automatically inserts
+    the ``scaletempo2`` audio filter.
+
 ``--pause``
     Start the player in paused state.
 

options/options.c

@@ -675,6 +675,7 @@ static const m_option_t mp_opts[] = {
     {"audio-channels", OPT_CHANNELS(audio_output_channels), .flags = UPDATE_AUDIO},
     {"audio-format", OPT_AUDIOFORMAT(audio_output_format), .flags = UPDATE_AUDIO},
     {"speed", OPT_DOUBLE(playback_speed), M_RANGE(0.01, 100.0)},
+    {"pitch", OPT_DOUBLE(playback_pitch), M_RANGE(0.01, 100.0)},
 
     {"audio-pitch-correction", OPT_BOOL(pitch_correction)},
 
@@ -1036,6 +1037,7 @@ static const struct MPOpts mp_default_opts = {
     .audio_display = 1,
     .audio_output_format = 0,  // AF_FORMAT_UNKNOWN
     .playback_speed = 1.,
+    .playback_pitch = 1.,
     .pitch_correction = true,
     .audiofile_auto = -1,
     .osd_bar_visible = true,
@@ -1127,6 +1129,7 @@ static const struct MPOpts mp_default_opts = {
     .watch_later_options = (char *[]){
         "start",
         "speed",
+        "pitch",
         "edition",
         "volume",
         "mute",

options/options.h

@@ -323,6 +323,7 @@ typedef struct MPOpts {
     int audio_output_format;
     int force_srate;
     double playback_speed;
+    double playback_pitch;
     bool pitch_correction;
     struct m_obj_settings *vf_settings;
     struct m_obj_settings *af_settings;

player/audio.c

@@ -54,6 +54,7 @@ static void update_speed_filters(struct MPContext *mpctx)
     if (!ao_c)
         return;
 
+    double pitch = mpctx->opts->playback_pitch;
     double speed = mpctx->opts->playback_speed;
     double resample = mpctx->speed_factor_a;
     double drop = 1.0;
@@ -66,14 +67,20 @@ static void update_speed_filters(struct MPContext *mpctx)
     if (mpctx->display_sync_active) {
         switch (mpctx->video_out->opts->video_sync) {
             case VS_DISP_ADROP:
-                drop *= speed * resample;
-                resample = speed = 1.0;
+                drop *= speed * resample / pitch;
+                resample = pitch;
+                speed = 1.0;
                 break;
             case VS_DISP_TEMPO:
-                speed = mpctx->audio_speed;
-                resample = 1.0;
+                speed = mpctx->audio_speed / pitch;
+                resample = pitch;
                 break;
+            default: goto normal;
         }
+    } else {
+normal:
+        resample *= pitch;
+        speed /= pitch;
     }
 
     mp_output_chain_set_audio_speed(ao_c->filter, speed, resample, drop);

player/command.c

@@ -431,6 +431,19 @@ static int mp_property_playback_speed(void *ctx, struct m_property *prop,
     return mp_property_generic_option(mpctx, prop, action, arg);
 }
 
+/// Playback pitch (RW)
+static int mp_property_playback_pitch(void *ctx, struct m_property *prop,
+                                      int action, void *arg)
+{
+    MPContext *mpctx = ctx;
+    if (action == M_PROPERTY_PRINT || action == M_PROPERTY_FIXED_LEN_PRINT) {
+        *(char **)arg = mp_format_double(NULL, mpctx->opts->playback_pitch, 2,
+                                         false, false, action != M_PROPERTY_FIXED_LEN_PRINT);
+        return M_PROPERTY_OK;
+    }
+    return mp_property_generic_option(mpctx, prop, action, arg);
+}
+
 static int mp_property_av_speed_correction(void *ctx, struct m_property *prop,
                                            int action, void *arg)
 {
@@ -3983,6 +3996,7 @@ static const struct m_property mp_properties_base[] = {
     // General
     {"pid", mp_property_pid},
     {"speed", mp_property_playback_speed},
+    {"pitch", mp_property_playback_pitch},
     {"audio-speed-correction", mp_property_av_speed_correction, .priv = "a"},
     {"video-speed-correction", mp_property_av_speed_correction, .priv = "v"},
     {"display-sync-active", mp_property_display_sync_active},
@@ -4402,6 +4416,7 @@ static const struct property_osd_display {
      .seek_bar = OSD_SEEK_INFO_BAR},
     {"hr-seek", "hr-seek"},
     {"speed", "Speed"},
+    {"pitch", "Pitch"},
     {"clock", "Clock"},
     {"edition", "Edition"},
     // audio
@@ -7438,7 +7453,8 @@ void mp_option_change_callback(void *ctx, struct m_config_option *co, int flags,
         run_command_opts(mpctx);
     }
 
-    if (opt_ptr == &opts->playback_speed) {
+    if (opt_ptr == &opts->playback_speed ||
+        opt_ptr == &opts->playback_pitch) {
         update_playback_speed(mpctx);
         mp_wakeup_core(mpctx);
     }