chromium/media/base/channel_layout.h

// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef MEDIA_BASE_CHANNEL_LAYOUT_H_
#define MEDIA_BASE_CHANNEL_LAYOUT_H_

#include "media/base/media_shmem_export.h"

namespace media {

// Enumerates the various representations of the ordering of audio channels.
// Logged to UMA, so never reuse a value, always add new/greater ones!
enum ChannelLayout { … };

// Note: Do not reorder or reassign these values; other code depends on their
// ordering to operate correctly. E.g., CoreAudio channel layout computations.
enum Channels { … };

// The maximum number of concurrently active channels for all possible layouts.
// ChannelLayoutToChannelCount() will never return a value higher than this.
constexpr int kMaxConcurrentChannels = …;

// Returns the expected channel position in an interleaved stream.  Values of -1
// mean the channel at that index is not used for that layout.  Values range
// from 0 to ChannelLayoutToChannelCount(layout) - 1.
MEDIA_SHMEM_EXPORT int ChannelOrder(ChannelLayout layout, Channels channel);

// Returns the number of channels in a given ChannelLayout or 0 if the
// channel layout can't be mapped to a valid value. Currently, 0
// is returned for CHANNEL_LAYOUT_NONE, CHANNEL_LAYOUT_UNSUPPORTED,
// CHANNEL_LAYOUT_DISCRETE, and CHANNEL_LAYOUT_BITSTREAM. For these cases,
// additional steps must be taken to manually figure out the corresponding
// number of channels.
MEDIA_SHMEM_EXPORT int ChannelLayoutToChannelCount(ChannelLayout layout);

// Given the number of channels, return the best layout,
// or return CHANNEL_LAYOUT_UNSUPPORTED if there is no good match.
MEDIA_SHMEM_EXPORT ChannelLayout GuessChannelLayout(int channels);

// Returns a string representation of the channel layout.
MEDIA_SHMEM_EXPORT const char* ChannelLayoutToString(ChannelLayout layout);

}  // namespace media

#endif  // MEDIA_BASE_CHANNEL_LAYOUT_H_