sdk/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.
type AudioFormat = struct {
    /// The type of individual samples.
    sample_format AudioSampleFormat;

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

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

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

    // 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.
type AudioSampleFormat = strict enum {
    UNSIGNED_8 = 1;
    SIGNED_16 = 2;
    SIGNED_24_IN_32 = 3;
    SIGNED_32 = 4;
    FLOAT = 5;
};

type AudioChannelLayout = strict union {
    1: placeholder uint8;
};

// 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.