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.
@available(added=7)
library fuchsia.mediacodec;

using fuchsia.media;
using fuchsia.math;
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.
type SecureMemoryMode = strict enum : uint32 {
    // Normal memory.  This is the default if a field of this type is not set.
    OFF = 0;
    // Secure memory.
    ON = 1;
};

type CreateDecoder_Params = table {
    /// 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: input_details fuchsia.media.FormatDetails;

    // 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, interpreted as false.
    2: promise_separate_access_units_on_input bool;

    // "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, interpreted as false.
    3: require_can_stream_bytes_input bool;

    /// 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, interpreted as false.
    4: require_can_find_start bool;

    /// 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, interpreted as false.
    5: require_can_re_sync bool;

    /// 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, interpreted as false.
    6: require_report_all_detected_errors bool;

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

    /// 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, interpreted as 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: permit_lack_of_split_header_handling bool;

    /// 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: secure_output_mode SecureMemoryMode;

    /// 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: secure_input_mode SecureMemoryMode;

    /// 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, interpreted as false.
   11: require_sw bool;
};

/// Parameters used to request an encoder.
type CreateEncoder_Params = table {
    /// 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: input_details fuchsia.media.FormatDetails;

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

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

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

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

/// Constrain the length of the vector indicated via `OnCodecList`, and constrain the max items in
/// any vector within the response from `GetDetailedCodecDescriptions`.  The overall enforced limit
/// for codec caps information is the max channel message size however, since nested vectors each of
/// max size could otherwise exceed the max channel message size.
const CODEC_FACTORY_CODEC_LIST_SIZE_MAX uint32 = 256;

/// Deprecated.
///
/// Rather than listening for OnCodecList, clients needing codec information prior to just
/// requesting a codec with CodecFactory.CreateDecoder or CodecFactory.CreateEncoder should instead
/// use GetDetailedCodecDescriptions to get the DetailedCodecDescription table instead, which has
/// per-profile-entry equivalents of all these fields.  Clients with no real need for codec
/// information prior to requesting a codec can call CodecFactory.CreateDecoder or
/// CodecFactory.CreateEncoder with relevant requirements set in that request, and then
/// StreamProcessor.Sync to see if a codec was actually created successfully.
///
/// In contrast to OnCodecList which uses FIDL structs (due to ordering of historical events),
/// GetDetailedCodecDescriptions uses FIDL tables so is not expected to need to be deprecated, since
/// we can add new table fields as needed, and gradually deprecate old table fields if appropriate,
/// without deprecating the whole thing.
///
/// Per-codec servers do not need to fill out this struct or send OnCodecList, as the main
/// CodecFactory will construct the OnCodecList info from the GetDetailedCodecDescriptions info, so
/// that each codec can (optionally) stop sending OnCodecList immediately, rather than having to
/// wait for all clients to stop listening to OnCodecList, which may take a while.  All codecs _do_
/// need to implement GetDetailedCodecDescriptions however.
@available(added=7, deprecated=11)
type CodecDescription = struct {
    /// Decoder or encoder.
    codec_type CodecType;
    /// 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.
    mime_type string:CODEC_FACTORY_MAX_MIME_TYPE_LENGTH;

    /// 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.
    @allow_deprecated_struct_defaults
    can_stream_bytes_input bool = true;
    @allow_deprecated_struct_defaults
    can_find_start bool = true;
    @allow_deprecated_struct_defaults
    can_re_sync bool = true;
    @allow_deprecated_struct_defaults
    will_report_all_detected_errors bool = true;
    @allow_deprecated_struct_defaults
    is_hw bool = true;
    @allow_deprecated_struct_defaults
    split_header_handling bool = true;
};

/// Specification of the supported parameters of a given video decoder.
///
/// Fields in this table with the same name as fields in CodecDescription have the same meaning as
/// the fields in the CodecDescription struct when the corresponding field in this table is set.
///
/// When a corresponding field is un-set, each of these fields is interpreted according to the
/// corresponding doc comment on the field in this table (doc comments on fields in the
/// CodecDescription struct re. struct field defaults are not relevant to the interpretation of
/// un-set fields of this table).
///
/// For video decoders, the following is always required:
///   * Handling split input payload (distinct from split header), when an input frame is too large
///     for a single input buffer.  The next portion (possibly the remainder) of the timstamped
///     input chunk is delivered in the next input packet.
///
/// For audio decoders, the following is always required:
///   * Concatenation of multiple compressed audio chunks via the input is always permitted.
@available(added=11)
type DecoderProfileDescription = table {
    /// The codec profile that this decoder supports. If the client wants to use this
    /// profile, the requirements specified in this table must be adhered to.
    1: profile fuchsia.media.CodecProfile;

    /// The minimum image size this decoder supports for the given |profile|.
    /// Decoders must set this field, and this field must specify a size that is
    /// >= the min size defined for the profile in the codec spec.
    ///
    /// This size refers to the pixel layout in memory, not the display_rect which can be smaller
    /// than the fuchsia.Images2.ImageFormat.size / fuchsia.sysmem.ImageFormat2.coded_width/height.
    2: min_image_size fuchsia.math.SizeU;

    /// The maximum image size this decoder supports for the given |profile|.
    ///
    /// Decoders must set this field, and this field must specify a size that is <= the max size
    /// defined for the profile in the codec spec.
    ///
    /// This size refers to the pixel layout in memory, not the display_rect which can be smaller
    /// than the fuchsia.Images2.ImageFormat.size / fuchsia.sysmem.ImageFormat2.coded_width/height.
    ///
    /// By setting this field, a decoder is not required to fail to decode a stream that specifies a
    /// size that is larger than the profile of the stream would normally allow. The decoder may or
    /// may not fail to decode a stream which is not a listed profile or not within the size bounds
    /// of a listed profile.
    3: max_image_size fuchsia.math.SizeU;

    /// This |profile| entry can apply to encrypted input data. If require_encryption is false or
    /// unset, this |profile| entry can also apply to unencrypted input data.
    ///
    /// This will be un-set (even when allow_input_protection or require_input_protection are true)
    /// until Fuchsia supports decryption as part of decode (in contrast to it being a separate step
    /// involving protected memory in between).  When allow_encryption is false/un-set but
    /// allow_input_protection is true, a client setting up DRM decode should set up decryption as a
    /// separate step prior to decode with protected memory in between the decrypt and decode.
    4: allow_encryption bool;

    /// This |profile| entry applies only when input data is encrypted.  This |profile| entry does
    /// not apply for unencrypted input data.  Un-set is interepted as false.
    ///
    /// If this is set to true and there is no profile with require_encryption false in the same
    /// DetailedCodecDescription, then this decoder only supports encrypted input.
    ///
    /// This will be un-set until Fuchsia supports decryption as part of decode (even when
    /// allow_input_protection or require_input_protection are true).  See also allow_encryption,
    /// allow_input_protection, require_input_protection.
    5: require_encryption bool;

    /// This |profile| entry can apply when input data delivered via protected memory.  Whether to
    /// protect input and which protected "heap" to use (if protecting input) is determined during
    /// sysmem constraints aggregation and via DRM mechanisms.  See also require_input_protection,
    /// allow_encryption, require_encryption.
    6: allow_input_protection bool;

    /// This |profile| entry applies only when input data is delivered via protected memory. Whether
    /// to protect input and which protected "heap" to use (if protecting input) is determined
    /// during sysmem constraints aggregation, and by separate DRM mechanisms.
    ///
    /// If this is set to true and there is no profile with require_input_protection false in the
    /// same DetailedCodecDescription, then this decoder only supports protected input.
    ///
    /// Output protection is negotiated separately during output buffer constraints aggregation in
    /// sysmem, and via DRM mechanisms.
    ///
    /// See also allow_input_protection, allow_encryption, require_encryption.
    7: require_input_protection bool;

    /// If set to true, the decoder can handle an input chunk payload (containing compressed data)
    /// that's split across a packet boundary (between header and payload, or between payload
    /// bytes), and the decoder can also handle more than one input chunk containing compressed
    /// input data in a single input packet. See also split_header_handling to determine if the
    /// decoder can also handle split headers.
    ///
    /// Un-set means false.
    ///
    /// While this field always indicates whether it's ok to split an input chunk across a packet
    /// boundary or not, and this field being set always implies it's ok to have a single input
    /// packet with bytes from more than one input chunk including when the input chunks contain
    /// compressed input data, there is some additional somewhat-subtle meaning that differs between
    /// video and audio decoders.
    ///
    /// Audio decoders are always required to permit more than one input chunk in a single input
    /// packet, including mulitple input chunks which each contain compressed input data (not just
    /// prepended "context" headers), regardless of this field being set or unset.  For audio
    /// decoders, this field only indicates whether splitting an input chunk across packets is
    /// allowed.
    ///
    /// Audio decoders shouldn't set split_header_handling to true unless they also set
    /// can_stream_bytes_input to true, since allowing splitting header bytes is meaningless unless
    /// it's allowed to split an input chunk.
    ///
    /// For video decoders, if this field is un-set or false, the decoder may not be able to handle
    /// bytes of more than one input chunk in a single input packet.  However, for all decoders
    /// (both video and audio) it's always ok for preceding "context" headers such as the h264 SPS
    /// and PPS headers to be in the same input packet as the following input chunk containing
    /// compressed input data such as an h264 slice (for example).  A video decoder is always
    /// required to permit continuation of an input chunk in the next packet, with the split between
    /// header byte and compressed input data byte or between two compressed input data bytes (but
    /// not necessarily between two header bytes; see also split_header_handling).
    ///
    /// It's expected to be fairly common for a decoder to set can_stream_bytes_input to true, but
    /// leave split_header_handling un-set or set split_header_handling to false, due to parsing
    /// limitations in the HW, FW, or driver.  Decoders which set can_stream_bytes_input false or
    /// leave can_stream_bytes_input un-set may be forcing input data to be re-packed in some
    /// scenarios.  Profiles which set allow_encryption are encouraged to also set
    /// can_stream_bytes_input if feasible, as re-packing input data can be more difficult in some
    /// scenarios involving encryption.
    8: can_stream_bytes_input bool;

    /// If set to true, the decoder can scan forward at the start of a stream to find the start of
    /// the first fully-present input chunk, even if the input data starts at a byte that's in the
    /// middle of a chunk.
    ///
    /// For both video and audio decoders, setting this field to true also indicates the ability to
    /// handle (skip or only partly use) any input chunks that are not possible to decode (or not
    /// possible to fully decode) due to lack of referenced prior data.
    ///
    /// If un-set or false, the decoder may not be able to scan forward to sync up with the input
    /// stream unless the input stream starts with the beginning of a suitable chunk.
    9: can_find_start bool;

    /// If set to true, the decoder can resynchronize with the input stream (eventually) despite a
    /// missing input chunk, and can handle partial input chunks without failing the stream or the
    /// StreamProcessor control connection.
   10: can_re_sync bool;

    /// If set to true, the decoder makes efforts to indicate partial or detected-as-missing or
    /// detected-as-corrupt input chunks by setting error_detected_before and/or
    /// error_detected_during as appropriate.  Even when this field is set to true, it is worth
    /// noting that in general it is not possible for a decoder to detect all possible data
    /// corruptions, as codecs generally aren't inclined to include error detection bits within the
    /// stream.  This is not a replacment for a real (as in robust with high probability against
    /// random bit flips and bit insertion/deletion) data integrity check.
   11: will_report_all_detected_errors bool;

    /// If set to true, the decoder can handle the bytes of any header being split across packet
    /// boundaries.  If false or un-set, the decoder requires all header bytes of a header to be
    /// within the same packet.
    ///
    /// Starting a new packet at the spec-defined boundary between two headers that are officially
    /// in separate input chunks is always permitted.
    ///
    /// For purposes of this field, headers like the h264 SPS and PPS headers are considered
    /// separate input chunks, and so such headers that have their own input chunk can be delivered
    /// in a separate packet regardless of the setting of this field, and a subsequent h264 slice
    /// header can be in yet another packet.
    ///
    /// It is always permissible regardless of the setting of this field for "context" headers (such
    /// as h264 SPS and PPS headers) to be delivered in the same packet as the subsequent chunk
    /// which conveys compressed image data (such as an h264 slice).
    ///
    /// Splitting a single header between codec_oob_bytes and the stream data is never supported (as
    /// in, never to be relied on by clients), not even when this field is set to true.
    ///
    /// See also can_stream_bytes_input.
    ///
    /// Video decoders with can_stream_bytes_input true but split_header_handling false can handle
    /// continuing an chunk in the next packet when split between header and payload or between
    /// payload bytes, and can handle bytes of more than one input chunk in a single input packet,
    /// but cannot handle splitting a header across packets. Video decoders with
    /// can_stream_bytes_input false and split_header_handling true cannot tolerate bytes of more
    /// than one input chunk in a single packet, but can tolerate continuation of an input chunk in
    /// a following packet regardless of where the split occurs (such as in the middle of an h264
    /// SPS, PPS, or slice header).
    ///
    /// Audio decoders shouldn't set split_header_handling to true unless they also set
    /// can_stream_bytes_input to true, since for an audio decoder, allowing splitting header bytes
    /// is meaningless (for audio decoders) unless also allowing splitting an input chunk.
   12: split_header_handling bool;
};

@available(added=11)
type EncoderProfileDescription = table {
    1: profile fuchsia.media.CodecProfile;

    // TODO(fxb/122519): Add additional table fields to indicate more detailed per-codec-profile
    // encoder caps.
};

@available(added=11)
type ProfileDescriptions = strict union {
    /// A list of |DecoderProfileDescription| that describe what codec profiles this
    /// decoder supports along with requirements that must be adhered to if the client
    /// is to use the decoder. The CodecFactory guarantees to the client that each
    /// |DecoderProfileDescription| within |decoder_profile_descriptions| will have an
    /// unique |profile|.
    1: decoder_profile_descriptions
            vector<DecoderProfileDescription>:CODEC_FACTORY_CODEC_LIST_SIZE_MAX;
    2: encoder_profile_descriptions
            vector<EncoderProfileDescription>:CODEC_FACTORY_CODEC_LIST_SIZE_MAX;
};

/// Clients needing codec information prior to just requesting a codec with
/// CodecFactory.CreateDecoder or CodecFactory.CreateEncoder should use GetDetailedCodecDescriptions
/// to get this table, which has details re. the codec and the profile entries supported by the
/// codec.
///
/// Clients with no real need for codec information prior to requesting a codec can simply use
/// CodecFactory.CreateDecoder or CodecFactory.CreateEncoder with relevant requirements set in that
/// request, and then call StreamProcessor.Sync (round trip) to see if a codec was created
/// successfully.
@available(added=11)
type DetailedCodecDescription = table {
    /// Decoder or encoder.
    1: codec_type CodecType;

    /// 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.
    2: mime_type string:CODEC_FACTORY_MAX_MIME_TYPE_LENGTH;

    /// If this decoder/encoder uses underlying hardware to perform its operations.
    3: is_hw bool;

    /// A list of profile descriptions that describe what codec profiles this
    /// encoder/decoder supports along with requirements for using each profile.
    4: profile_descriptions ProfileDescriptions;
};

// 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.
    //
    // TODO(fxb/122622): Remove OnCodecList when possible.
    @available(added=7, deprecated=11, note="use GetDetailedCodecDescriptions()")
    -> OnCodecList(struct {
        codecs vector<CodecDescription>:CODEC_FACTORY_CODEC_LIST_SIZE_MAX;
    });

    // Requests:

    /// A client should call |GetDetailedCodecDescriptions()| to get a list of
    /// codecs supported either by software implementations or by underlying hardware.
    @available(added=11)
    GetDetailedCodecDescriptions() -> (table {
        1: codecs vector<DetailedCodecDescription>:CODEC_FACTORY_CODEC_LIST_SIZE_MAX;
    });

    /// 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(resource struct {
        decoder_params CreateDecoder_Params;
        decoder server_end:fuchsia.media.StreamProcessor;
    });

    /// 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(resource struct {
        encoder_params CreateEncoder_Params;
        encoder server_end:fuchsia.media.StreamProcessor;
    });

    /// AttachLifetimeTracking:
    ///
    /// Attach an eventpair endpoint to the next Create{X}(), so that the
    /// codec_end will be closed when the number of buffers allocated reaches
    /// 'buffers_remaining'.  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 created internally
    /// by the codec.  The sysmem buffer collections visible to the client, for
    /// input and output buffers, are not included in the resources tracked
    /// here, because those can be tracked separately via
    /// fuchsia.sysmem.BufferCollection.AttachLifetimeTracking().  It is
    /// permitted to send a duplicate of codec_end to both this
    /// AttachLifetimeTracking() and also to
    /// fuchsia.sysmem.BufferCollection.AttachLifetimeTracking().
    /// The ZX_EVENTPAIR_PEER_CLOSED will happen when both/all lifetimes are
    /// fully over.  This conveniently avoids needing multiple separate async
    /// waits by the client.
    ///
    /// 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).
    AttachLifetimeTracking(resource struct {
        codec_end zx.handle:EVENTPAIR;
    });
};