sdk/fidl/fuchsia.mediacodec/codec_factory.fidl

// Copyright 2018 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.mediacodec;

using fuchsia.media;
using zx;

// CreateDecoder_Params
//
// Input parameters for creating a decoder (audio or video).
//

/// Whether buffers need to be secure.  If not specified, the default is OFF.
///
/// This enum may have additional values added later; code handling this type
/// should be written with this in mind.  For example, in C++, having a
/// "default" case in any switch statement on this type will avoid compilation
/// warnings/errors when a new value is added.
//
// Later we can add DYNAMIC, as needed.
enum SecureMemoryMode : uint32 {
    // Normal memory.  This is the default if a field of this type is not set.
    OFF = 0;
    // Secure memory.
    ON = 1;
};

table CreateDecoder_Params {
    /// Input mime type for a decoder.
    ///
    /// The recognized mime types for now:
    /// video/h264
    /// video/vp9
    /// audio/aac
    ///   input_details.oob_bytes must be an AudioSpecificConfig() as defined
    ///   by AAC spec.
    /// audio/sbc
    ///   input_details.oob_bytes must be Codec Specific Information Elements
    ///   for SBC as defined by the A2DP spec.
    1: fuchsia.media.FormatDetails input_details;

    // The settings below nail down more details.

    /// This must be true in order for the client to be permitted to put a
    /// timestamp on an input packet, which is in turn required to get any
    /// timestamps on any output packets.
    ///
    /// It is always legal to provide separate Access Units (henceforth AUs) to a
    /// decoder, but this boolean must be true for a decoder to accept and
    /// propagate timestamp values.
    ///
    /// This must be true when creating a video encoder, or the CodecFactory
    /// channel will close.
    ///
    /// If not set, defaults to false.
    2: bool promise_separate_access_units_on_input;

    // "require" fields:
    //
    // Specifying any of these "require" fields can result in failure to get a
    // Codec if there's no suitable codec.  None of these correspond to any
    // required features of a codec server.
    //
    // TODO(dustingreen): implement filtering codecs based on these fields.

    /// Require that the selected codec be capable of accepting input where
    /// AUs are not separated into separate packets.
    ///
    /// This does not imply that the decoder can find the start of the first AU;
    /// for that see require_can_find_start.  This does not imply that the decoder
    /// can re-sync on its own if the stream data is damaged; for that see
    /// require_can_re_sync.
    ///
    /// If both promise_separate_access_units_on_input and
    /// require_can_stream_bytes_input are true, the CodecFactory channel will
    /// close.
    ///
    /// If this is false, the client must feed separate AUs on the fuchsia.ui.input.  This
    /// must be false for a video encoder, and if true the CodecFactory channel
    /// will close.
    ///
    /// Unless a client demands a decoder capable of taking concatenated AUs
    /// (require_can_stream_bytes_input true), the client must feed a decoder
    /// separate AUs.  This means the client cannot have parts of two separate AUs
    /// in the same packet, unless require_can_stream_bytes_input is true.
    ///
    /// If not set, defaults to false.
    3: bool require_can_stream_bytes_input;

    /// A decoder is allowed to be capable of streaming bytes but not capable of
    /// searching for the start of the first usable AU.  To require both, set both
    /// require_can_stream_bytes_input and require_can_find_start.  Setting
    /// require_can_find_start without require_can_stream_bytes_input is invalid.
    ///
    /// With require_can_stream_bytes_input true but require_can_find_start false,
    /// the client must start the first packet with the start of an AU, but can
    /// send a stream of bytes after that.
    ///
    /// If not set, defaults to false.
    4: bool require_can_find_start;

    /// On problematic input data, all decoders are expected to at least be able to
    /// close the channel rather than getting stuck in a failed and/or broken
    /// state.
    ///
    /// A decoder returned from a request with require_can_re_sync is potentially
    /// able to handle damaged input without closing the Codec channel.  Such a
    /// Codec is encouraged, but not required, to also satisfy requirements of
    /// require_report_all_detected_errors.
    ///
    /// If not set, defaults to false.
    5: bool require_can_re_sync;

    /// Sometimes a client would rather fail an overall use of a decoder than fail
    /// to notice data corruption.  For such scenarios, the client can specify
    /// require_report_all_detected_errors.  For any codec returned from a
    /// request with require_report_all_detected_errors set, on detection of
    /// any input data corruption the codec will report in one or more of these
    /// ways:
    ///   * closing the Codec channel
    ///   * OnStreamFailed()
    ///   * error_detected_before
    ///   * error_detected_during
    ///
    /// If false, a codec may silently skip past corrupted input data.
    ///
    /// No decoder can detect all corruption, because some corruption can look like
    /// valid stream data.  This requirement is only to request a codec that
    /// is written to attempt to detect _and report_ input stream corruption.
    ///
    /// This flag is not intended to be 100% bulletproof.  If a client needs robust
    /// assurance that _all_ detectable stream corruption is _always_ detected,
    /// this flag is not enough of a guarantee to achieve that.  Since some stream
    /// corruption is inherently non-detectable in any case, such a client should
    /// consider using stronger techniques upstream to ensure that corruption can
    /// be detected with the needed probability very close to 1.
    ///
    /// This flag being true doesn't imply anything about whether the codec will
    /// discard damaged data vs. producing corresponding damaged output.  Only that
    /// the codec will set error_detected_* bools to true when appropriate.
    ///
    /// Regardless of this setting, not all timestamp_ish values provided on input
    /// are guaranteed to show up on output.
    ///
    /// If not set, defaults to false.
    6: bool require_report_all_detected_errors;

    /// If true, require that the returned codec is HW-accelerated.  See also
    /// `require_sw`.
    ///
    /// If not set, defaults to false.
    7: bool require_hw;

    /// permit_lack_of_split_header_handling
    ///
    /// This field is a temporary field that will be going away.
    ///
    /// TODO(dustingreen): Remove this field once we're down to zero codecs with
    /// problems handling split headers.
    ///
    /// By default, a Codec instance is required to handle "split headers", meaning
    /// that a client is allowed to deliver parts of an AU one byte at a time,
    /// including parts near the beginning of the AU, and the codec is required to
    /// tolerate and handle that properly.  However, unfortunately not all codecs
    /// properly support split headers.  If a client is willing to permit such a
    /// codec to be used, the client can set this to true.  Clients are not
    /// encouraged to set this, but setting it may be necessary to find a codec for
    /// some formats _for now_.  If a client sets this to true, the client should
    /// deliver data of each AU with many contiguous non-split bytes from the start
    /// of each AU.  The client is not strictly required to deliver one AU at a
    /// time, only to ensure that either all the AU bytes are in a single packet or
    /// that many bytes at the start of each AU are in a single packet.
    ///
    /// The specification for how a client should use this and how a client should
    /// behave if setting this to true is intentionally vague, because lack of
    /// support for header splitting is not ideal, and is expected to be
    /// temporary, and all codecs should handle split headers in the long run.
    /// The main intent of this field is to avoid giving an innocent client using
    /// default value of false here a codec that can't properly handle split
    /// headers.  This is not an attempt at a mechanism to fully work around a
    /// codec that doesn't handle split headers.
    ///
    /// If not set, defaults to false.
    //
    // TODO(dustingreen): In the near term, wire this up so that SoftAAC2.cpp
    // used for ADTS is not selected when this field is false, even if there is
    // no other suitable codec.  In the long term, fix or work around the header
    // handling behavior of SoftAAC2 when used in ADTS mode (and any other
    // similar issues in other codecs) and remove this field.
    8: bool permit_lack_of_split_header_handling;

    /// If set to ON, the decoder must support secure buffers on output, and
    /// must reject non-secure buffers on output.
    ///
    /// If set to OFF or not set, the created decoder will reject secure buffers
    /// on output by closing the StreamProcessor channel.
    ///
    /// If secure_input_mode ON, secure_output_mode must also be ON.
    9: SecureMemoryMode secure_output_mode;

    /// If set to ON, the decoder must support secure buffers on input and must
    /// reject non-secure buffers on input.
    ///
    /// If set to OFF or not set, the created decoder will reject secure buffers
    /// on input by closing the StreamProcessor channel.
    ///
    /// If secure_input_mode ON, secure_output_mode must also be ON.
    10: SecureMemoryMode secure_input_mode;

    /// If true, require that the returned codec is entirely SW-based, not
    /// HW-accelerated (other than possibly using vector CPU instructions).
    /// This can be useful for testing purposes or other special scenarios, but
    /// is not recommended for performance-sensitive scenarios.  Also, some
    /// builds may lack a SW-based decoder for some formats.  See also
    /// `require_hw`.
    ///
    /// If not set, defaults to false.
    11: bool require_sw;
};

/// Parameters used to request an encoder.
table CreateEncoder_Params {
    /// The format of the uncompressed input data.
    ///
    /// This field should be a raw mime_type (e.g. 'video/raw') and uncompressed
    /// format details for the encoder to use when reading buffers.
    ///
    /// To be elibigible an encoder must support the input format.
    1: fuchsia.media.FormatDetails input_details;

    /// If true, require that the returned codec is HW-accelerated.
    ///
    /// If not set, defaults to false.
    2: bool require_hw;
};

enum CodecType {
    DECODER = 0;
    ENCODER = 1;
};

/// Constrain the mime_type to a size that won't cause problems.
const uint32 CODEC_FACTORY_MAX_MIME_TYPE_LENGTH = 256;

struct CodecDescription {
    /// Decoder or encoder.
    CodecType codec_type;
    /// The mime type of the compressed format.  For decoders this is the mime
    /// type of the input.  For encoders, this is the mime type of the output.
    string:CODEC_FACTORY_MAX_MIME_TYPE_LENGTH mime_type;

    // TODO(dustingreen): All these fields should be optional.
    //
    // TODO(dustingreen): Re-evaluate this for encoders.
    //
    /// For each of these fields, the default is the most-capable setting, but
    /// if a codec doesn't support the most-capable behavior, then the codec
    /// must override the default.
    bool can_stream_bytes_input = true;
    bool can_find_start = true;
    bool can_re_sync = true;
    bool will_report_all_detected_errors = true;
    bool is_hw = true;
    bool split_header_handling = true;
};

/// More than this many calls to AttachLifetimeTracking()
/// without a Create{X}() call will result in CodecFactory channel closing from
/// the server end.
const uint32 CODEC_FACTORY_LIFETIME_TRACKING_EVENTPAIR_PER_CREATE_MAX = 16;

/// Constrain the length of the codec list.
const uint32 CODEC_FACTORY_CODEC_LIST_SIZE_MAX = 256;

/// CodecFactory
///
/// The purpose of the media::CodecFactory interface is to create
/// media::StreamProcessor instances for decoders and encoders.
///
/// The interface methods don't attempt to homogenize all codec types,
/// preferring to have a separate dedicated message for decoders.
[Discoverable]
protocol CodecFactory {
    /// Driver-based local CodecFactory(s) will send this once shortly after the
    /// main CodecFactory connects to the driver-local CodecFactory.
    ///
    /// For now, the main CodecFactory will not send this.
    ///
    /// A SW-based local CodecFactory(s) will not send this event.
    ///
    /// Each codec in the list must be separately-described, for clean aggregation.
    -> OnCodecList(vector<CodecDescription>:CODEC_FACTORY_CODEC_LIST_SIZE_MAX codecs);

    // Requests:

    /// CreateDecoder:
    ///
    /// decoder_params - See CreateDecoder_Params comments for required
    /// and optional parameters for creating a decoder.
    ///
    /// decoder - a Codec.NewRequest() which will hopefully be connected to
    /// a Codec server, or the Codec channel will get closed if no suitable
    /// codec can be found.  We don't return any additional Codec-specific
    /// status here because finding the Codec is allowed to be fully async, so
    /// we don't necessarily yet know on return from this method which Codec
    /// will be selected, if any.
    ///
    /// Rough sequence to create a decoder:
    ///
    /// factory = ConnectToEnvironmentService(CodecFactory);
    /// CreateDecoder_Params params;
    /// [fill out params]
    /// CreateDecoder(params, decoder_request);
    ///
    /// See use_media_decoder code for more detail.
    CreateDecoder(
        CreateDecoder_Params decoder_params,
        request<fuchsia.media.StreamProcessor> decoder);

    /// CreateEncoder:
    ///
    /// encoder_params - See CreateEncoder_Params comments for required
    /// and optional parameters for creating a decoder.
    ///
    /// encoder - a Codec.NewRequest() which will hopefully be connected to
    /// a Codec server, or the Codec channel will get closed if no suitable
    /// codec can be found.  We don't return any additional Codec-specific
    /// status here because finding the Codec is allowed to be fully async, so
    /// we don't necessarily yet know on return from this method which Codec
    /// will be selected, if any.
    CreateEncoder(CreateEncoder_Params encoder_params,
                  request<fuchsia.media.StreamProcessor> encoder);

    /// AttachLifetimeTracking:
    ///
    /// Attach an eventpair endpoint to the next Create{X}(), so that the
    /// codec_end will signal ZX_EVENTPAIR_PEER_CLOSED on the peer of codec_end
    /// shortly after the created codec is gone.  Multiple eventpair endpoints
    /// can be attached per create, with an enforced limit of
    /// CODEC_FACTORY_LIFETIME_TRACKING_EVENTPAIR_PER_CREATE_MAX.
    ///
    /// The lifetime signalled by this event is intended to track all resources
    /// used by the codec, including sysmem-allocated buffers.
    ///
    /// In the case of server process crashes, or failure of a codec to plumb
    /// codec_end to sysmem, ZX_EVENTPAIR_PEER_CLOSED signalled on the peer of
    /// codec_end may occur shortly before all resources are freed.
    ///
    /// A maximum of CODEC_FACTORY_LIFETIME_TRACKING_EVENTPAIR_PER_CREATE_MAX
    /// calls to AttachLifetimeTracking() are allowed
    /// before any Create{X}().  There is no way to cancel an attach short of
    /// closing the CodecFactory channel.  Closing the client end of the
    /// eventpair doesn't subtract from the number of pending attach(es).  For
    /// this reason, it can be good to only send attach message(s) immediately
    /// before the relevant Create{X}(), when it's known by the client that both
    /// the attach message(s) and the Create{X}() messages will be sent.
    ///
    /// Closing the client's end doesn't result in any action by the server.
    /// If the server listens to events from the client end at all, it is for
    /// debug logging only.
    ///
    /// The server intentionally doesn't "trust" any bits signalled by the
    /// client.  This mechanism intentionally uses only ZX_EVENTPAIR_PEER_CLOSED
    /// which can't be triggered early, and is only triggered when all handles
    /// to codec_end are closed.  No meaning is associated with any of the other
    /// signal bits, and clients should functionally ignore any other signal
    /// bits on either end of the eventpair or its peer.
    ///
    /// The codec_end may lack ZX_RIGHT_SIGNAL or ZX_RIGHT_SIGNAL_PEER, but must
    /// have ZX_RIGHT_DUPLICATE (and must have ZX_RIGHT_TRANSFER to transfer
    /// without causing CodecFactory channel failure).
    [Transitional = "AttachLifetimeTracking() not yet implemented"]
    AttachLifetimeTracking(
        zx.handle:EVENTPAIR codec_end);
};