Aegisub/aegisub/src/audio_provider_downmix.cpp

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// Copyright (c) 2007-2008, Niels Martin Hansen
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// * Redistributions of source code must retain the above copyright notice,
// this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above copyright notice,
// this list of conditions and the following disclaimer in the documentation
// and/or other materials provided with the distribution.
// * Neither the name of the Aegisub Group nor the names of its contributors
// may be used to endorse or promote products derived from this software
// without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.
//
// Aegisub Project http://www.aegisub.org/
//
// $Id$
/// @file audio_provider_downmix.cpp
/// @brief Intermediate audio provider downmixing the signal to mono
/// @ingroup audio_input
///
//////////////////
// Headers
#include "config.h"
#include "audio_provider_downmix.h"
/// @brief Constructor
/// @param source
///
DownmixingAudioProvider::DownmixingAudioProvider(AudioProvider *source) : provider(source) {
filename = source->GetFilename();
channels = 1; // target
src_channels = source->GetChannels();
num_samples = source->GetNumSamples();
bytes_per_sample = source->GetBytesPerSample();
sample_rate = source->GetSampleRate();
if (!(bytes_per_sample == 1 || bytes_per_sample == 2))
throw AudioOpenError("Downmixing Audio Provider: Can only downmix 8 and 16 bit audio");
if (!source->AreSamplesNativeEndian())
throw AudioOpenError("Downmixing Audio Provider: Source must have machine endian samples");
}
/// @brief Actual work happens here
/// @param buf
/// @param start
/// @param count
///
void DownmixingAudioProvider::GetAudio(void *buf, int64_t start, int64_t count) const {
if (count == 0) return;
// We can do this ourselves
if (start >= num_samples) {
if (bytes_per_sample == 1)
// 8 bit formats are usually unsigned with bias 127
memset(buf, 127, count);
else
// While everything else is signed
memset(buf, 0, count*bytes_per_sample);
return;
}
// So alloc some temporary memory for this
// Depending on use, this might be made faster by using
// a pre-allocced block of memory...?
char *tmp = new char[count*bytes_per_sample*src_channels];
try {
provider->GetAudio(tmp, start, count);
}
catch (...) {
delete tmp;
throw;
}
// Now downmix
// Just average the samples over the channels (really bad if they're out of phase!)
// XXX: Assuming here that sample data are in machine endian, an upstream provider should ensure that
if (bytes_per_sample == 1) {
uint8_t *src = (uint8_t *)tmp;
uint8_t *dst = (uint8_t *)buf;
while (count > 0) {
int sum = 0;
for (int c = 0; c < src_channels; c++)
sum += *(src++);
*(dst++) = (uint8_t)(sum / src_channels);
count--;
}
}
else if (bytes_per_sample == 2) {
int16_t *src = (int16_t *)tmp;
int16_t *dst = (int16_t *)buf;
while (count > 0) {
int sum = 0;
for (int c = 0; c < src_channels; c++)
sum += *(src++);
*(dst++) = (int16_t)(sum / src_channels);
count--;
}
}
// Done downmixing, free the work buffer
delete[] tmp;
}