mpd/src/CrossFade.cxx

/*
 * Copyright (C) 2003-2013 The Music Player Daemon Project
 * http://www.musicpd.org
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#include "config.h"
#include "CrossFade.hxx"
#include "MusicChunk.hxx"
#include "AudioFormat.hxx"
#include "util/Domain.hxx"
#include "Log.hxx"

#include <cmath>

#include <assert.h>
#include <string.h>
#include <stdlib.h>

static constexpr Domain cross_fade_domain("cross_fade");

#ifdef WIN32

static char *
strtok_r(char *str, const char *delim, gcc_unused char **saveptr)
{
	return strtok(str, delim);
}

#endif

static float mixramp_interpolate(char *ramp_list, float required_db)
{
	float db, secs, last_db = nan(""), last_secs = 0;
	char *ramp_str, *save_str = nullptr;

	/* ramp_list is a string of pairs of dBs and seconds that describe the
	 * volume profile. Delimiters are semi-colons between pairs and spaces
	 * between the dB and seconds of a pair.
	 * The dB values must be monotonically increasing for this to work. */

	while (1) {
		/* Parse the dB tokens out of the input string. */
		ramp_str = strtok_r(ramp_list, " ", &save_str);

		/* Tell strtok to continue next time round. */
		ramp_list = nullptr;

		/* Parse the dB value. */
		if (nullptr == ramp_str)
			return nan("");

		db = (float)atof(ramp_str);

		/* Parse the time. */
		ramp_str = strtok_r(nullptr, ";", &save_str);
		if (nullptr == ramp_str)
			return nan("");

		secs = (float)atof(ramp_str);

		/* Check for exact match. */
		if (db == required_db) {
			return secs;
		}

		/* Save if too quiet. */
		if (db < required_db) {
			last_db = db;
			last_secs = secs;
			continue;
		}

		/* If required db < any stored value, use the least. */
		if (std::isnan(last_db))
			return secs;

		/* Finally, interpolate linearly. */
		secs = last_secs + (required_db - last_db) * (secs - last_secs) / (db - last_db);
		return secs;
	}
}

unsigned cross_fade_calc(float duration, float total_time,
			 float mixramp_db, float mixramp_delay,
			 float replay_gain_db, float replay_gain_prev_db,
			 char *mixramp_start, char *mixramp_prev_end,
			 const AudioFormat af,
			 const AudioFormat old_format,
			 unsigned max_chunks)
{
	unsigned int chunks = 0;
	float chunks_f;
	float mixramp_overlap;

	if (duration < 0 || duration >= total_time ||
	    /* we can't crossfade when the audio formats are different */
	    af != old_format)
		return 0;

	assert(duration >= 0);
	assert(af.IsValid());

	chunks_f = (float)af.GetTimeToSize() / (float)CHUNK_SIZE;

	if (std::isnan(mixramp_delay) || !mixramp_start || !mixramp_prev_end) {
		chunks = (chunks_f * duration + 0.5);
	} else {
		/* Calculate mixramp overlap. */
		mixramp_overlap = mixramp_interpolate(mixramp_start, mixramp_db - replay_gain_db)
		  + mixramp_interpolate(mixramp_prev_end, mixramp_db - replay_gain_prev_db);
		if (!std::isnan(mixramp_overlap) &&
		    mixramp_delay <= mixramp_overlap) {
			chunks = (chunks_f * (mixramp_overlap - mixramp_delay));
			FormatDebug(cross_fade_domain,
				    "will overlap %d chunks, %fs", chunks,
				    mixramp_overlap - mixramp_delay);
		}
	}

	if (chunks > max_chunks) {
		chunks = max_chunks;
		LogWarning(cross_fade_domain,
			   "audio_buffer_size too small for computed MixRamp overlap");
	}

	return chunks;
}