player_thread: move cross-fading to output thread

Remove cross_fade_apply(), and call pcm_mix() in the output thread,
mixing the chunk and chunk->other together.

src/chunk.h

@@ -50,6 +50,12 @@ struct music_chunk {
 	 */
 	struct music_chunk *other;
 
+	/**
+	 * The current mix ratio for cross-fading: 1.0 means play 100%
+	 * of this chunk, 0.0 means play 100% of the "other" chunk.
+	 */
+	float mix_ratio;
+
 	/** number of bytes stored in this chunk */
 	uint16_t length;
 

src/crossfade.c

@@ -131,46 +131,3 @@ unsigned cross_fade_calc(float duration, float total_time,
 
 	return chunks;
 }
-
-void cross_fade_apply(struct music_chunk *a, const struct music_chunk *b,
-		      const struct audio_format *format,
-		      float mix_ratio)
-{
-	size_t size;
-
-	assert(a != NULL);
-	assert(b != NULL);
-	assert(a->length == 0 || b->length == 0 ||
-	       audio_format_equals(&a->audio_format, &b->audio_format));
-
-	if (a->tag == NULL && b->tag != NULL)
-		/* merge the tag into the destination chunk */
-		a->tag = tag_dup(b->tag);
-
-	size = b->length > a->length
-		? a->length
-		: b->length;
-
-	pcm_mix(a->data,
-		b->data,
-		size,
-		format,
-		mix_ratio);
-
-	if (b->length > a->length) {
-		/* the second buffer is larger than the first one:
-		   there is unmixed rest at the end.  Copy it over.
-		   The output buffer API guarantees that there is
-		   enough room in a->data. */
-
-#ifndef NDEBUG
-		if (a->length == 0)
-			a->audio_format = b->audio_format;
-#endif
-
-		memcpy(a->data + a->length,
-		       b->data + a->length,
-		       b->length - a->length);
-		a->length = b->length;
-	}
-}

src/crossfade.h

@@ -45,18 +45,4 @@ unsigned cross_fade_calc(float duration, float total_time,
 			 const struct audio_format *old_format,
 			 unsigned max_chunks);
 
-/**
- * Applies cross fading to two chunks, i.e. mixes these chunks.
- * Internally, this calls pcm_mix().
- *
- * @param a the chunk in the current song (and the destination chunk)
- * @param b the according chunk in the new song
- * @param format the audio format of both chunks (must be the same)
- * @param current_chunk the relative index of the current chunk
- * @param num_chunks the number of chunks used for cross fading
- */
-void cross_fade_apply(struct music_chunk *a, const struct music_chunk *b,
-		      const struct audio_format *format,
-		      float mix_ratio);
-
 #endif

src/output_control.c

@@ -301,4 +301,6 @@ void audio_output_finish(struct audio_output *ao)
 	g_mutex_free(ao->mutex);
 
 	filter_free(ao->filter);
+
+	pcm_buffer_deinit(&ao->cross_fade_buffer);
 }

src/output_init.c

@@ -191,6 +191,8 @@ audio_output_init(struct audio_output *ao, const struct config_param *param,
 	ao->pause = false;
 	ao->fail_timer = NULL;
 
+	pcm_buffer_init(&ao->cross_fade_buffer);
+
 	/* set up the filter chain */
 
 	ao->filter = filter_chain_new();

src/output_internal.h

@@ -21,6 +21,7 @@
 #define MPD_OUTPUT_INTERNAL_H
 
 #include "audio_format.h"
+#include "pcm_buffer.h"
 
 #include <glib.h>
 
@@ -134,6 +135,11 @@ struct audio_output {
 	 */
 	struct audio_format out_audio_format;
 
+	/**
+	 * The buffer used to allocate the cross-fading result.
+	 */
+	struct pcm_buffer cross_fade_buffer;
+
 	/**
 	 * The filter object of this audio output.  This is an
 	 * instance of chain_filter_plugin.

src/output_thread.c

@@ -24,6 +24,7 @@
 #include "chunk.h"
 #include "pipe.h"
 #include "player_control.h"
+#include "pcm_mix.h"
 #include "filter_plugin.h"
 #include "filter/convert_filter_plugin.h"
 #include "filter/replay_gain_filter_plugin.h"
@@ -299,6 +300,35 @@ ao_filter_chunk(struct audio_output *ao, const struct music_chunk *chunk,
 		ao->replay_gain_serial = chunk->replay_gain_serial;
 	}
 
+	/* cross-fade */
+
+	if (chunk->other != NULL) {
+		size_t other_length;
+		const char *other_data = ao_chunk_data(ao, chunk->other,
+						       &other_length);
+		if (other_length == 0) {
+			*length_r = 0;
+			return data;
+		}
+
+		/* if the "other" chunk is longer, then that trailer
+		   is used as-is, without mixing; it is part of the
+		   "next" song being faded in, and if there's a rest,
+		   it means cross-fading ends here */
+
+		if (length > other_length)
+			length = other_length;
+
+		char *dest = pcm_buffer_get(&ao->cross_fade_buffer,
+					    other_length);
+		memcpy(dest, other_data, other_length);
+		pcm_mix(dest, data, length, &ao->in_audio_format,
+			1.0 - chunk->mix_ratio);
+
+		data = dest;
+		length = other_length;
+	}
+
 	/* apply filter chain */
 
 	data = filter_filter(ao->filter, data, length, &length, &error);

src/player_thread.c

@@ -651,10 +651,9 @@ play_next_chunk(struct player *player)
 		}
 
 		if (other_chunk != NULL) {
-			float mix_ratio;
-
 			chunk = music_pipe_shift(player->pipe);
 			assert(chunk != NULL);
+			assert(chunk->other == NULL);
 
 			/* don't send the tags of the new song (which
 			   is being faded in) yet; postpone it until
@@ -665,16 +664,13 @@ play_next_chunk(struct player *player)
 			other_chunk->tag = NULL;
 
 			if (isnan(pc.mixramp_delay_seconds)) {
-				mix_ratio = ((float)cross_fade_position)
+				chunk->mix_ratio = ((float)cross_fade_position)
 					     / player->cross_fade_chunks;
 			} else {
-				mix_ratio = nan("");
+				chunk->mix_ratio = nan("");
 			}
 
-			cross_fade_apply(chunk, other_chunk,
+			chunk->other = other_chunk;
-					 &dc->out_audio_format,
-					 mix_ratio);
-			music_buffer_return(player_buffer, other_chunk);
 		} else {
 			/* there are not enough decoded chunks yet */