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// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// Software adjust volume of samples, allows each audio stream its own
// volume without impacting master volume for chrome and other applications.
// Implemented as templates to allow 8, 16 and 32 bit implementations.
// 8 bit is unsigned and biased by 128.
// TODO(vrk): This file has been running pretty wild and free, and it's likely
// that a lot of the functions can be simplified and made more elegant. Revisit
// after other audio cleanup is done. (crbug.com/120319)
#include "media/audio/audio_util.h"
#include "base/command_line.h"
#include "base/string_number_conversions.h"
#include "base/time.h"
#include "media/base/media_switches.h"
#if defined(OS_WIN)
#include "base/win/windows_version.h"
#endif
namespace media {
// Returns user buffer size as specified on the command line or 0 if no buffer
// size has been specified.
int GetUserBufferSize() {
const CommandLine* cmd_line = CommandLine::ForCurrentProcess();
int buffer_size = 0;
std::string buffer_size_str(cmd_line->GetSwitchValueASCII(
switches::kAudioBufferSize));
if (base::StringToInt(buffer_size_str, &buffer_size) && buffer_size > 0)
return buffer_size;
return 0;
}
// Computes a buffer size based on the given |sample_rate|. Must be used in
// conjunction with AUDIO_PCM_LINEAR.
size_t GetHighLatencyOutputBufferSize(int sample_rate) {
int user_buffer_size = GetUserBufferSize();
if (user_buffer_size)
return user_buffer_size;
// TODO(vrk/crogers): The buffer sizes that this function computes is probably
// overly conservative. However, reducing the buffer size to 2048-8192 bytes
// caused crbug.com/108396. This computation should be revisited while making
// sure crbug.com/108396 doesn't happen again.
// The minimum number of samples in a hardware packet.
// This value is selected so that we can handle down to 5khz sample rate.
static const size_t kMinSamplesPerHardwarePacket = 1024;
// The maximum number of samples in a hardware packet.
// This value is selected so that we can handle up to 192khz sample rate.
static const size_t kMaxSamplesPerHardwarePacket = 64 * 1024;
// This constant governs the hardware audio buffer size, this value should be
// chosen carefully.
// This value is selected so that we have 8192 samples for 48khz streams.
static const size_t kMillisecondsPerHardwarePacket = 170;
// Select the number of samples that can provide at least
// |kMillisecondsPerHardwarePacket| worth of audio data.
size_t samples = kMinSamplesPerHardwarePacket;
while (samples <= kMaxSamplesPerHardwarePacket &&
samples * base::Time::kMillisecondsPerSecond <
sample_rate * kMillisecondsPerHardwarePacket) {
samples *= 2;
}
return samples;
}
#if defined(OS_WIN)
int NumberOfWaveOutBuffers() {
// Use the user provided buffer count if provided.
int buffers = 0;
std::string buffers_str(CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
switches::kWaveOutBuffers));
if (base::StringToInt(buffers_str, &buffers) && buffers > 0) {
return buffers;
}
// Use 4 buffers for Vista, 3 for everyone else:
// - The entire Windows audio stack was rewritten for Windows Vista and wave
// out performance was degraded compared to XP.
// - The regression was fixed in Windows 7 and most configurations will work
// with 2, but some (e.g., some Sound Blasters) still need 3.
// - Some XP configurations (even multi-processor ones) also need 3.
return (base::win::GetVersion() == base::win::VERSION_VISTA) ? 4 : 3;
}
#endif
} // namespace media
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