Aegisub/libaegisub/audio/provider_convert.cpp

// Copyright (c) 2014, Thomas Goyne <plorkyeran@aegisub.org>
//
// Permission to use, copy, modify, and distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
//
// Aegisub Project http://www.aegisub.org/

#include "libaegisub/audio/provider.h"

#include <libaegisub/log.h>
#include <libaegisub/make_unique.h>

#include <limits>

using namespace agi;

/// Anything -> mono 16 bit signed machine-endian audio converter
namespace {
class ConvertAudioProvider final : public AudioProviderWrapper {
public:
	ConvertAudioProvider(std::unique_ptr<AudioProvider> src) : AudioProviderWrapper(std::move(src)) {
		float_samples = false;
		channels = 1;
		bytes_per_sample = sizeof(int16_t);
	}

	void FillBuffer(void *buf, int64_t start, int64_t count) const override {
		source->GetInt16MonoAudio(reinterpret_cast<int16_t*>(buf), start, count);
	}
};

/// Sample doubler with linear interpolation for the samples provider
/// Requires 16-bit mono input
class SampleDoublingAudioProvider final : public AudioProviderWrapper {
public:
	SampleDoublingAudioProvider(std::unique_ptr<AudioProvider> src) : AudioProviderWrapper(std::move(src)) {
		sample_rate *= 2;
		num_samples *= 2;
		decoded_samples = decoded_samples * 2;
	}

	void FillBuffer(void *buf, int64_t start, int64_t count) const override {
		int16_t *src, *dst = static_cast<int16_t *>(buf);

		// We need to always get at least two samples to be able to interpolate
		int16_t srcbuf[2];
		if (count == 1) {
			source->GetAudio(srcbuf, start / 2, 2);
			src = srcbuf;
		}
		else {
			source->GetAudio(buf, start / 2, (start + count) / 2 - start / 2 + 1);
			src = dst;
		}

		// walking backwards so that the conversion can be done in place
		for (; count > 0; --count) {
			auto src_index = (start + count - 1) / 2 - start / 2;
			auto i = count - 1;
			if ((start + i) & 1)
				dst[i] = (int16_t)(((int32_t)src[src_index] + src[src_index + 1]) / 2);
			else
				dst[i] = src[src_index];
		}
	}
};
}

namespace agi {
std::unique_ptr<AudioProvider> CreateConvertAudioProvider(std::unique_ptr<AudioProvider> provider) {
	// Ensure 16-bit audio with proper endianness
	if (provider->AreSamplesFloat())
		LOG_D("audio_provider") << "Converting float to S16";
	else if (provider->GetBytesPerSample() != 2)
		LOG_D("audio_provider") << "Converting " << provider->GetBytesPerSample() << " bytes per sample to S16";

	// We currently only support mono audio
	if (provider->GetChannels() != 1)
		LOG_D("audio_provider") << "Downmixing to mono from " << provider->GetChannels() << " channels";

	provider = agi::make_unique<ConvertAudioProvider>(std::move(provider));

	// Some players don't like low sample rate audio
	while (provider->GetSampleRate() < 32000) {
		LOG_D("audio_provider") << "Doubling sample rate";
		provider = agi::make_unique<SampleDoublingAudioProvider>(std::move(provider));
	}

	return provider;
}
}