src/media/vnext/fidl/fuchsia.mediastreams/audio_format.fidl

// Copyright 2021 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

library fuchsia.mediastreams;

/// Describes a format used for audio elementary streams without
/// reference to compression. Where compression is supported, this
/// type should be combined with a `Compression` struct.
struct AudioFormat {
    /// The type of individual samples.
    AudioSampleFormat sample_format;

    /// The number of samples per frame.
    uint32 channel_count;

    /// The number of frames per second.
    uint32 frames_per_second;

    /// The spatial assignment of each channel.
    AudioChannelLayout channel_layout;

    // TODO: Maybe add bytes_per_frame for convenience. It’s
    // a function of sample_format and channel_count.
};

/// Expresses the format of individual audio samples.
enum AudioSampleFormat {
    UNSIGNED_8 = 1;
    SIGNED_16 = 2;
    SIGNED_24_IN_32 = 3;
    FLOAT = 4;
};

union AudioChannelLayout {
    1: uint8 placeholder;
};

// TODO: Define AudioChannelLayout
// There are essentially four ways to do this:
// 1) an enum of layouts, which restricts layouts to those represented
//    in the enum,
// 2) a ‘bits’ type of individual channel assignments, which allows
//    any combination of the represented channel assignments but
//    restricts their permutation,
// 3) a vector of enum values of individual channel assignments, which
//    allows any permutation of the represented channel assignments,
//    or
// 4) a collection of fold-down tables that indicate how the channels
//    should be mixed to produce other channel configurations.
// These are listed in increasing order of expressiveness and
// decreasing order of ergonomics. We need to decide which
// representation(s) we want to support.